THE REPUBLIC OF MAURITIUS MINISTRY OF PUBLIC INFRASTRUCTURE AND LAND TRANSPORT (MPI)
THE PROJECT OF LANDSLIDE MANAGEMENT IN THE REPUBLIC OF MAURITIUS
FINAL REPORT
MAIN REPORT
March 2015
JAPAN INTERNATIONAL COOPERATION AGENCY KOKUSAI KOGYO CO., LTD. NIPPON KOEI CO., LTD. GE CENTRAL CONSULTANT INC. JR FUTABA INC. 15-044 THE REPUBLIC OF MAURITIUS MINISTRY OF PUBLIC INFRASTRUCTURE AND LAND TRANSPORT (MPI)
THE PROJECT OF LANDSLIDE MANAGEMENT IN THE REPUBLIC OF MAURITIUS
FINAL REPORT
MAIN REPORT
March 2015
JAPAN INTERNATIONAL COOPERATION AGENCY KOKUSAI KOGYO CO., LTD. NIPPON KOEI CO., LTD. CENTRAL CONSULTANT INC. FUTABA INC.
Location of Study Area 20°0'0"E 30°0'0"E 40°0'0"E 50°0'0"E 60°0'0"E 70°0'0"E 80°0'0"E
20°0'0"N 20°0'0"N
10°0'0"N 10°0'0"N
0°0'0" 0°0'0"
Republic of Mauritius 10°0'0"S 10°0'0"S
20°0'0"S 20°0'0"S 0500 1,000 2,000 km 20°0'0"E 30°0'0"E 40°0'0"E 50°0'0"E 60°0'0"E 70°0'0"E 80°0'0"E Detai l Map
Vallee Pitot La Butte
Chitrakoot
Quatre Soeurs
Location Map
Rate of Currency Translation
1 USD = 34.959 Rs = 119.68 JPY
100 Rs = 3.098 USD = 370.75 JPY Rs: Mauritius Rupee
As of March 1st, 2015
Photos of the Project (1)
Courtesy visit to the Deputy Prime Minister and Conclusion on commencement of the Project, 30th Minister of MPI, 28th May 2012 May 2012
1st Steering Committee, 29th May 2012 2nd Steering Committee, 1st Nov. 2012
3rd Steering Committee, 21st Nov. 2013 4th Steering Committee, 19th Jan. 2015 Photos of the Project (2)
1st Stakeholder Meeting (Chitrakoot), 22nd Sep. 2nd Stakeholder Meeting (Quatre Soeurs), 12th Apr. 2012 2013
5th Stakeholder Meeting (Vallee Pitot), 12th Dec. 1st Technical Transfer Seminar, 10th Oct. 2012 2014
2nd Technical Transfer Seminar, 20th Nov. 2013 3rd Technical Transfer Seminar, 20th Jan. 2015
Photos of the Project (3)
Site visit by IOC, 13th Jun. 2012 4th Technical Workshop 【Landuse Policy】, 30th Jul. 2012
5th Technical Workshop 【Aerial Photo 10th Technical Workshop 【Stability Analysis and Interpretation】, 6th Sep. 2012 Countermeasures】, 5th Mar. 2013
1st Training in Japan, 2nd Training in Japan, 24th Nov. ~ 15th Dec. 2012 17th Aug. ~ 8th Sep. 2013
Photos of the Project (4)
Boring Survey (Quatre Soeurs), 2nd Oct. 2012 Technical Guidance on Horizontal Drilling for Landslide Countermeasure Works (Chitrakoot), 30th Oct. 2014
2nd Site Meeting for the Construction of Landslide Completed Countermeasure Work 【River Countermeasure Works (Chitrakoot), 1st Sep. 2014 Type-3】, 12th Dec. 2014
Completed Countermeasure Work 【Bridge Completed Countermeasure Work 【Horizontal Type-3】, 12th Dec. 2014 Drainage】, 12th Dec. 2014
CONTENTS
Location Map Photos Contents List of Figures List of Tables List of Photos Abbreviations Digest
Page
1 Introduction ...... 1-1 1.1 General ...... 1-1 1.2 Background of the Project ...... 1-1 1.3 Objectives of the Project ...... 1-2 1.3.1 Objective ...... 1-2 1.3.2 Desired Outcome ...... 1-2 1.3.3 Outcome of the Project ...... 1-2 1.4 Scope of the Project ...... 1-3 1.4.1 Project Areas ...... 1-3 1.4.2 List of JICA Expert Team and Counterparts ...... 1-4 1.5 Major Activities ...... 1-5
2 Basic Survey ...... 2-1 2.1 Topography ...... 2-1 2.2 Geology and Rainfall ...... 2-2 2.3 Landslide Inventory Survey ...... 2-5 2.3.1 Classification of Hazard Area ...... 2-7 2.3.2 Site Reconnaissance ...... 2-9 2.3.3 Inventory and Location Map ...... 2-17 2.3.4 GIS Database ...... 2-21 2.4 Existing Countermeasures ...... 2-25 2.4.1 Structural Countermeasures ...... 2-25 2.4.2 Non-Structural Countermeasures ...... 2-26 2.5 Social Survey ...... 2-28 2.5.1 Basic Information Survey ...... 2-28 2.5.2 Attitude Survey about Landslide Disasters ...... 2-34 2.6 Organizations and Systems ...... 2-38 2.6.1 Organizational and Institutional Formation ...... 2-38 2.7 Economic Survey ...... 2-43 2.7.1 National Economic Indicators ...... 2-43 2.7.2 National Economic Policies in Mauritius ...... 2-44 2.7.3 Fiscal Policy for 2014 ...... 2-46
i 2.7.4 Fiscal Policy of the Ministry of Public Infrastructure (MPI) 2014-2016 ...... 2-47 2.7.5 Budget for LMU ...... 2-49
3 Landslide Management Plan 1 (Survey and Results) ...... 3-1 3.1 Landslide Hazard Area ...... 3-1 3.2 Topographic Survey ...... 3-3 3.2.1 Specifications ...... 3-3 3.2.2 Deliverables ...... 3-3 3.3 Geological Survey ...... 3-7 3.3.1 Geology of the Landslide Area ...... 3-7 3.3.2 Laboratory Test ...... 3-11 3.3.3 Water Quality Analysis ...... 3-31 3.4 Monitoring ...... 3-35 3.4.1 Installation of Monitoring Devices ...... 3-35 3.4.2 Monitoring Results ...... 3-38 3.5 Geophysical Exploration ...... 3-50 3.5.1 Elastic Wave Exploration...... 3-50 3.5.2 Two-Dimensional Resistivity Exploration ...... 3-59 3.6 Drilling Survey ...... 3-68 3.6.1 Drilling Plan ...... 3-68 3.6.2 Core Drilling ...... 3-70 3.6.3 Installation of Observation Equipment ...... 3-73 3.6.4 Drilling Results ...... 3-78 3.6.5 Standard Penetration Test ...... 3-79 3.7 Field Reconnaissance ...... 3-82 3.7.1 Damage to Houses ...... 3-82 3.7.2 Results of Field Reconnaissance ...... 3-89 3.8 Disaster Inspection ...... 3-120 3.8.1 Significance and Objectives of Disaster Inspection ...... 3-121 3.8.2 Method of Disaster Inspection ...... 3-122 3.8.3 Results of Disaster Inspection ...... 3-122 3.8.4 Recommendation on Disaster Inspection ...... 3-125 3.9 Review and Recommendations for the Disaster Scheme ...... 3-128 3.9.1 Review of the Existing Warning System of Landslides in Mauritius ...... 3-128 3.9.2 Recommendation for the Disaster Scheme ...... 3-131 3.10 Review and Recommendations for the Planning Policy Guidance ...... 3-150 3.10.1 Review of Japanese Legal Systems for Landslide Countermeasures ...... 3-151 3.10.2 The existing Legal Systems/schemes for LDRM in Mauritius ...... 3-157 3.10.3 Existing Situation of Landslide Prone Areas in Mauritius ...... 3-159 3.10.4 Recommendation of PPG ...... 3-166 3.11 Technical Guideline for Initial Survey ...... 3-179 3.12 Procedure Manual for Landslide ...... 3-181
4 Landslide Management Plan 2 (Analysis and Interpretation) ... 4-1 4.1 Geological Interpretation ...... 4-1 4.1.1 Chitrakoot ...... 4-1 4.1.2 Quatre Soeurs ...... 4-4 4.1.3 Vallee Pitot ...... 4-6 4.2 Interpretation of Monitoring ...... 4-8
ii 4.2.1 Chitrakoot ...... 4-8 4.2.2 Quatre Soeurs ...... 4-11 4.2.3 Vallee Pitot ...... 4-12 4.3 Consideration of Threshold for Soil Water Index ...... 4-13 4.3.1 Method of Analysis ...... 4-13 4.3.2 Data ...... 4-15 4.3.3 Result of SWI Calculation ...... 4-18 4.3.4 Introduction of SWI in Mauritius ...... 4-26 4.4 Stability Analysis ...... 4-28 4.4.1 Factor of Safety ...... 4-28 4.4.2 Setting Parameters ...... 4-30 4.4.3 Method of Stability Analysis ...... 4-31 4.4.4 Stability Analysis ...... 4-33 4.4.5 Evaluation of the Soil Strength ...... 4-48 4.5 Susceptibility Assessment ...... 4-51
5 Feasibility Study ...... 5-1 5.1 Priority Site and Pilot Project site ...... 5-1 5.1.1 Selection of Priority Site ...... 5-1 5.1.2 Selection of Pilot Project Site ...... 5-2 5.1.3 Disaster Scenario at the Pilot Project Site ...... 5-3 5.2 Policy of Countermeasures ...... 5-6 5.2.1 Plan for Countermeasures Works in Chitrakoot ...... 5-7 5.2.2 Emergency Works in Vallee Pitot ...... 5-18 5.2.3 Relocation in Quatre Soeurs ...... 5-24 5.3 Environmental Impact Assessment (EIA) ...... 5-26 5.3.1 Procedure of Environmental Impact Assessment...... 5-26 5.3.2 EIA Related to Pilot Project ...... 5-28 5.3.3 Main Environmental and Social Impacts and Mitigation Measures ...... 5-29 5.4 Pilot Project Evaluation ...... 5-30 5.4.1 Pre Evaluation ...... 5-30 5.4.2 Interim Review ...... 5-32 5.4.3 Post Evaluation ...... 5-34 5.5 Promotion of Fund Raising ...... 5-36 5.6 Organizational Reinforcement Plan ...... 5-41 5.6.1 Capacity Development Plan ...... 5-41 5.6.2 Landslide Management Unit (LMU) in MPI ...... 5-41 5.6.3 Issues, Goals and Activities in Capacity Development for Medium and Long Term Plan ...... 5-43 5.6.4 Outcomes Achieved and Future Capacity Development Plan ...... 5-47
6 Pilot Project (Landslide Countermeasures) ...... 6-1 6.1 Structural Countermeasures ...... 6-1 6.1.1 Basic design of Countermeasure Works ...... 6-1 6.1.2 Detailed Design of Countermeasure Works in Chitrakoot ...... 6-9 6.1.3 Plan for Construction ...... 6-21 6.1.4 Preparation of Bidding Documents and Bidding ...... 6-23 6.1.5 Supervision ...... 6-29 6.1.6 Design Changes ...... 6-29 6.1.7 Future Plan ...... 6-30 6.1.8 Available Countermeasure Works in Mauritius ...... 6-34 6.1.9 Development in the Landslide Hazard Zone after the Landslide
iii Countermeasure Works ...... 6-35 6.2 Early Warning and Evacuation ...... 6-37 6.2.1 Present Situation and Issue in Mauritius ...... 6-37 6.2.2 Proposal of Early Warning and Evacuation System ...... 6-39 6.2.3 Establishment of Early Warning and Evacuation System ...... 6-48 6.3 Information, Education and Communication (IEC) ...... 6-53 6.3.1 IEC in the Landslide Management Project ...... 6-53 6.3.2 Current Status and Issues of IEC activities in the Field of Landslide Management in Mauritius ...... 6-53 6.3.3 IEC Activities to be Implemented by the Project ...... 6-56 6.3.4 Stakeholder Meeting for Residents at Priority Areas ...... 6-57 6.3.5 Questionnaire Survey for Residents at Three Priority Area ...... 6-66 6.3.6 Project Newsletter ...... 6-69 6.3.7 IEC Material - Landslide Disaster Prevention Handbook - ...... 6-69 6.4 Technical Summary of the Pilot Project ...... 6-71
7 Technical Transfer ...... 7-1 7.1 Methodology ...... 7-1 7.1.1 Objectives of Technical Transfer ...... 7-1 7.1.2 Method of Technical Transfer ...... 7-1 7.1.3 Basic policy of Technical Transfer ...... 7-2 7.2 Structure of Technical Transfer ...... 7-3 7.3 Technical Transfer Seminar ...... 7-4 7.3.1 1st Technical Transfer Seminar ...... 7-4 7.3.2 2nd Technical Transfer Seminar ...... 7-4 7.3.3 3rd Technical Transfer Seminar ...... 7-6 7.4 Workshop ...... 7-7 7.5 Training in Japan ...... 7-16 7.6 Steering Committee ...... 7-21 7.7 Advisory Committee in Japan ...... 7-26 7.8 Results of Technical Transfer ...... 7-29 7.9 Future Plans by MPI and the Related Organizations ...... 7-32 7.9.1 Future Plans by MPI ...... 7-32 7.9.2 Future Plans by the Related Organizations ...... 7-35
8 Environment, Climate Change Adaptation and Disaster Management ...... 8-1 8.1 General ...... 8-1 8.2 Landslide Management and the Environment, Climate Change Adaptation and Disaster Management ...... 8-3 8.3 The Project and Related Organizations ...... 8-4 8.3.1 Government Agencies and Organization of Mauritius ...... 8-4 8.3.2 Development Partners ...... 8-5 8.4 Summary on Environment, Climate Change Adaptation and Disaster Management by JICA ...... 8-9 8.5 Technical Exchange with the Southwest Indian Ocean Islands ...... 8-12 8.5.1 Summary of the Regional Seminar ...... 8-13
iv 9 Proposal for Future Tasks ...... 9-1 9.1 Proposal on a Landslide Management Plan ...... 9-1 9.1.1 Disaster Inspection ...... 9-1 9.1.2 Disaster Scheme ...... 9-1 9.1.3 Recommendation of PPG ...... 9-2 9.1.4 Technical Guideline for Initial Survey ...... 9-3 9.1.5 Procedure Manual for Landslide ...... 9-4 9.2 Proposal on a Feasibility Study ...... 9-6 9.2.1 Promotion of Fund Raising ...... 9-6 9.2.2 Organizational Reinforcement Plan ...... 9-10 9.3 Proposal on a Pilot Project (Landslide Countermeasures) ...... 9-17 9.3.1 Structural Countermeasures (Future Plan) ...... 9-17 9.3.2 Development in the Landslide Hazard Zone after the Landslide Countermeasure Works ...... 9-22 9.3.3 Early Warning and Evacuation System...... 9-23 9.3.4 Information, Education and Communication (IEC) ...... 9-25 9.4 Proposal on a Landslide Management Plan for Other Landslide Areas . 9-27 9.4.1 Hypothesis on Landslides in Mauritius ...... 9-27 9.4.2 Proposal on Formulation of a Landslide Management Plan ...... 9-28
v Supporting Report
Volume 1 1. Minutes of Meeting on the Detailed Planning Survey for the Project 2. Minutes of Meeting on 1st Steering Committee 3. Minutes of Meeting on 2nd Steering Committee 4. Minutes of Meeting on 3rd Steering Committee 5. Minutes of Meeting on 4th Steering Committee 6. Landslide Location Map 7. Landslide Recording Sheet 8. Result of Aerial Photograph Interpretation 9. The Survey Result of Landslide Awareness of Residents 10. Regular Check Sheets and Photo Sheets 11. Bore Logs and Core Sample Photo 12. Soil Test and Water Quality 13. Review and Recommendation for the Disaster Scheme 14. Review and Recommendation for the Planning Policy Guidance 15. Result of Stability Analysis 16. Project Leaflet (Project of Landslide Management in the Republic of Mauritius) 17. Presentation Material for 1st Stakeholder Meeting 18. Presentation Material for 2nd Stakeholder Meeting 19. Minutes of 1st Technical Seminar 20. Minutes of 2nd Technical Seminar 21. Minutes of 1st Advisory Committee in Japan 22. Minutes of 2nd Advisory Committee in Japan 23. Minutes of 3rd Advisory Committee in Japan 24. Minutes of 4th Advisory Committee in Japan
Volume 2 25. Reports of Technical Advice of Individual Site for MPI 26. Soil Water Index 27. Result of Ring Shear Test 28. Calculation of Pile Work 29. Results of Stability Analysis of Slope behind the Drainage 30. Consideration of the Cross Section for Drainage 31. Drawings for the Landslide Countermeasure 32. Documents related to the Modification of Drawings 33. Cost estimation 34. Construction Supervision Report
vi List of Figures
Page Figure 1.4.1 Location Map of the Project Area ...... 1-3 Figure 1.5.1 Flowchart of Project Activity ...... 1-7 Figure 2.1.1 Full View Map of Mauritius ...... 2-1 Figure 2.2.1 Geological Map of Mauritius ...... 2-2 Figure 2.2.2 Cross Section of the Typical Landslide (Colluvial Landslide): La Butte Landslide ..... 2-3 Figure 2.2.3 Annual Rainfall Amount in Mauritius (1971~2000) ...... 2-4 Figure 2.3.1 Example of the Result of Aerial Photograph interpretation - Chitrakoot area ...... 2-11 Figure 2.3.2 Schematic Diagram of Landslide Landforms ...... 2-12 Figure 2.3.3 Example of the Landslide Recording Sheet, Chitrakoot Area ...... 2-14 Figure 2.3.4 Example of the Landslide Recording Sheet, Vallee Pitot Area ...... 2-15 Figure 2.3.5 Example of the Landslide Recording Sheet, Quatre Soeurs ...... 2-16 Figure 2.3.6 Landslide Location Map ...... 2-17 Figure 2.3.7 Flow to Create A Database Using the ArcGIS ...... 2-21 Figure 2.3.8 Sample of Link of Political Boundary Map and Attribute Data ...... 2-23 Figure 2.3.9 Landslide Survey location Map (Base Map: Topographic Map(1:25,000)) ...... 2-24 Figure 2.3.10 Landslide Survey location Map (Base Map: Roads, River, contour line, Province Boundary) ...... 2-24 Figure 2.3.11 Landslide Distribution Map, Chitrakoot Area ...... 2-24 Figure 2.3.12 Landslide Distribution Map, Quatre Soeurs Area ...... 2-24 Figure 2.4.1 The Landslide Structural Countermeasures in La Butte Area ...... 2-26 Figure 2.5.1 Land Use Map ...... 2-28 Figure 2.5.2 Population Distribution Map ...... 2-30 Figure 2.5.3 Poverty Distribution Map ...... 2-31 Figure 2.5.4 Distribution Map of Principal Water Resources in Mauritius ...... 2-32 Figure 3.2.1 Chitrakoot, Plan Map ...... 3-4 Figure 3.2.2 Chitrakoot, Cross Section ...... 3-4 Figure 3.2.3 Quatre Soeurs, Plan Map ...... 3-5 Figure 3.2.4 Quatre Soeurs, Cross Section ...... 3-5 Figure 3.2.5 Vallee Pitot, Plan Map ...... 3-6 Figure 3.2.6 Vallee Pitot, Cross Section ...... 3-6 Figure 3.3.1 Topographic Map of the Site ...... 3-7 Figure 3.3.2 Aerial Photograph of the Site ...... 3-7 Figure 3.3.3 Location of the Site on Geological Map ...... 3-9 Figure 3.3.4 An Explanatory Drawing of Peak Strength and Residual Strength ...... 3-12 Figure 3.3.5 Typical Particle Size Distribution of Slip Surface Soil for Each Geological Zone in Japan...... 3-13 Figure 3.3.6 Relation of Plasticity Index and Residual Shear Stress Angle for Various Geological Zones ...... 3-14 Figure 3.3.7 Structure of Cyclic Shear Test Device ...... 3-16 Figure 3.3.8 Relation between Shear Stress and Accumulative Shear Displacement ...... 3-16 Figure 3.3.9 Measuring the Friction Force between Two Shear Boxes ...... 3-16 Figure 3.3.10 Method of Determining Strength Factor for Design Using C-Tanφ Diagram ...... 3-17 Figure 3.3.11 Structure of Shear-Test Device ...... 3-17 Figure 3.3.12 Method of Making Test Piece That Includes Slip Surface ...... 3-17 Figure 3.3.13 Structure of Triaxial Shear Test Device ...... 3-19 Figure 3.3.14 Atterberg Limits ...... 3-23 Figure 3.3.15 Sampling Location (Chitrakoot) ...... 3-25 Figure 3.3.16 Sampling Location (Quatre Soeurs) ...... 3-26 Figure 3.3.17 Sampling Location (Vallee Pitot) ...... 3-26 Figure 3.3.18 Difference between Direct Shearing Test and Ring Shear Test ...... 3-27 Figure 3.3.19 Shearing Characteristic of Normally-Consolidated Clay and Overconsolidated Clay ...... 3-28 Figure 3.3.20 Structural Drawing of the Ring Shear Apparatus ...... 3-28 Figure 3.3.21 Test Specimen Rough Sketch ...... 3-28
vii Figure 3.3.22 Examination Process of Ring Shear Test ...... 3-29 Figure 3.3.23 Example of Hexadiagram ...... 3-32 Figure 3.3.24 Hexadiagram in the Groundwater at Chitrakoot ...... 3-34 Figure 3.3.25 Hexadiagram in the Groundwater at Quatre Soeurs ...... 3-34 Figure 3.4.1 Basic Landslide Monitoring Techniques ...... 3-36 Figure 3.4.2 Plan of Instrument Installation – Chitrakoot ...... 3-36 Figure 3.4.3 Plan of Instrument Installation – Quatre Soeurs ...... 3-37 Figure 3.4.4 Plan of Instrument Installation – Vallee Pitot ...... 3-37 Figure 3.4.5 Result of Rain Gauge ...... 3-38 Figure 3.4.6 Results of Extensometer ...... 3-40 Figure 3.4.7 Results of Inclinometer ...... 3-40 Figure 3.4.8 Vertical Stress at Head of Landslide ...... 3-41 Figure 3.4.9 Results of Strain Gauges ...... 3-42 Figure 3.4.10 Results of Piezometer ...... 3-43 Figure 3.4.11 Result of Rain Gauge ...... 3-44 Figure 3.4.12 Result of Laser Distance Meter ...... 3-45 Figure 3.4.13 Results of Strain Gauges ...... 3-46 Figure 3.4.14 Groundwater at BH-Q2 ...... 3-46 Figure 3.4.15 Results of Piezometer ...... 3-47 Figure 3.4.16 Water Level in The Boreholes ...... 3-48 Figure 3.4.17 Location of Extensometers ...... 3-49 Figure 3.4.18 Results of Extensometer ...... 3-49 Figure 3.4.19 Tension Movement at EV2 ...... 3-49 Figure 3.5.1 Location of Seismic Survey Lines at Chitrakoot ...... 3-51 Figure 3.5.2 The Seismic Wave ...... 3-52 Figure 3.5.3 Travel Time Curves and Seismic Paths ...... 3-52 Figure 3.5.4 DAQ LINK ⅡSystem and Measured Image ...... 3-53 Figure 3.5.5 Observation Procedure and Diagram of Observation ...... 3-53 Figure 3.5.6 Travel-time Curve of A1-1 Line ...... 3-55 Figure 3.5.7 Analytical Diagram of Velocity Profile of A1-1 Line ...... 3-55 Figure 3.5.8 Seismic Velocity Section (A1-line) ...... 3-57 Figure 3.5.9 Seismic Velocity Section (A2-line) ...... 3-57 Figure 3.5.10 Seismic Velocity Section (B1-line) ...... 3-57 Figure 3.5.11 Seismic Velocity Section (B2A-line) ...... 3-58 Figure 3.5.12 Seismic Velocity Section (B2B-line) ...... 3-58 Figure 3.5.13 Seismic Velocity Section (C-line) ...... 3-58 Figure 3.5.14 Location of Resistivity Survey Lines in Chitrakoot ...... 3-60 Figure 3.5.15 Measuring Equipment (SYSCAL R1 PLUS Switch-72) and Pole Bolt ...... 3-61 Figure 3.5.16 Electrode Arrays for 2-Pole Method ...... 3-61 Figure 3.5.17 High-Density Electrical Resistivity Exploration Measuring Method ...... 3-62 Figure 3.5.18 Resistivity Inversion Analysis Flow ...... 3-63 Figure 3.5.19 Resistivity Sequence of A1-1 Line ...... 3-64 Figure 3.5.20 Resistivity Pseudosection (A1-line) according to Inverse Analysis ...... 3-65 Figure 3.5.21 Resistivity Pseudosection (A2-line) according to Inverse Analysis ...... 3-65 Figure 3.5.22 Resistivity Pseudosection (B1-line) according to Inverse Analysis ...... 3-66 Figure 3.5.23 Resistivity Pseudosection (B2A-line) according to Inverse Analysis ...... 3-66 Figure 3.5.24 Resistivity Pseudosection (B2B-line) according to Inverse Analysis ...... 3-67 Figure 3.5.25 Resistivity Pseudosection (C-line) according to Inverse Analysis ...... 3-67 Figure 3.6.1 Survey Locations in Chitrakoot ...... 3-69 Figure 3.6.2 Survey locations in Quatre Soeurs ...... 3-70 Figure 3.7.1 Results of Survey on Damage to Houses, Chitrakoot ...... 3-83 Figure 3.7.2 Monitoring Locations of the Damaged Houses ...... 3-85 Figure 3.7.3 Past Newspaper Report ...... 3-88 Figure 3.7.4 Results of Survey on Damage to Houses, Vallee Pitot ...... 3-88 Figure 3.7.5 Slope classification of the area ...... 3-104 Figure 3.7.6 Landslide Plan Map, 1st Reconnaissance in 2012 ...... 3-115 Figure 3.7.7 Landslide Plan Map (3rd Reconnaissance on 26th February 2013) ...... 3-119
viii Figure 3.8.1 Situation of the Inspection for Slope Disasters ...... 3-121 Figure 3.8.2 Example of Regular Check Sheet ...... 3-122 Figure 3.8.3 Location Map of Rank As ( ) including Chitrakoot, Vallee Pitot and Quatre Soeurs ...... 3-126 Figure 3.9.1 Outline Image of the Draft Recommendation for Disaster Scheme ...... 3-131 Figure 3.10.1 Process for Making Recommendation for PPG ...... 3-150 Figure 3.10.2 Japanese Legal Systems for Landslide Countermeasures ...... 3-151 Figure 3.10.3 Conceptual Image of Non-Physical Countermeasure Implementation by the Landslide Disasters Prevention Act ...... 3-154 Figure 3.10.4 Summary of the Landslide Disasters Prevention Act ...... 3-155 Figure 3.10.5 Acts and Schemes related with PPG ...... 3-159 Figure 3.10.6 Strategy Plan of Port Louis (Chitrakoot is shown in Black Frame) ...... 3-160 Figure 3.10.7 Building Distribution in Landslide Risk Area of Chitrakoot ...... 3-161 Figure 3.10.8 Development Restriction in Quatre Soeurs ...... 3-162 Figure 3.10.9 Strategy Plan of Port Louis (Vallée Pitot is shown in Black Frame) ...... 3-164 Figure 3.10.10 The Damaged Area and Building Distribution in Vallée Pitot ...... 3-164 Figure 3.10.11 Outline Image of the Draft Recommendation for PPG ...... 3-166 Figure 3.11.1 The Scope of Application of the Technical Guideline for Initial Survey ...... 3-179 Figure 3.12.1 The Scope of Application of the Procedure Manual for Landslides ...... 3-181 Figure 4.1.1 Landslide Blocks in Chitrakoot ...... 4-1 Figure 4.1.2 Geological Section of Block A (North- South) ...... 4-2 Figure 4.1.3 Geological Section of Block B (North- South) ...... 4-3 Figure 4.1.4 Geological Section of Whole Area of Chitrakoot (North- South) ...... 4-3 Figure 4.1.5 Landslide Blocks in Quatre Soeurs...... 4-4 Figure 4.1.6 Geological Section of Slopes in Quatre Soeurs ...... 4-5 Figure 4.1.7 Landslide Blocks in Vallee Pitot ...... 4-6 Figure 4.1.8 Assumed Landslide Slips in Vallee Pitot along Red Line in Figure 4.1.7 ...... 4-7 Figure 4.2.1 Record of the Extensometers in Block A in Chitrakoot ...... 4-8 Figure 4.2.2 Groundwater Levels in Chitrakoot Monitored by Piezometers ...... 4-9 Figure 4.2.3 Picture of BPP(13) in March 2013 ...... 4-10 Figure 4.3.1 Image of SWI Model ...... 4-14 Figure 4.3.2 3-Steps of Tank Model ...... 4-14 Figure 4.3.3 Example of Daily Rainfall Data Divided into 24 Hours ...... 4-16 Figure 4.3.4 Comparison between GSMaP Data and Rain Gauge Data ...... 4-17 Figure 4.3.5 The Role of Disaster Record in SWI ...... 4-18 Figure 4.3.6 SWI and Cumulative Precipitation in Chitrakoot (2005, MMS) ...... 4-19 Figure 4.3.7 SWI and Cumulative Precipitation in Chitrakoot (2006, MMS) ...... 4-20 Figure 4.3.8 SWI and Cumulative Precipitation in Chitrakoot (2008, MMS) ...... 4-20 Figure 4.3.9 SWI and Cumulative Precipitation in Chitrakoot (2005, GSMaP) ...... 4-21 Figure 4.3.10 SWI and Cumulative Precipitation in Chitrakoot (2006, GSMaP) ...... 4-21 Figure 4.3.11 SWI and Cumulative Precipitation in Chitrakoot (2008, GSMaP) ...... 4-21 Figure 4.3.12 SWI and Cumulative Precipitation in Quatre Soeurs (2005, MMS) ...... 4-24 Figure 4.3.13 SWI and Cumulative Precipitation in Quatre Soeurs (2008, MMS) ...... 4-24 Figure 4.3.14 SWI and Cumulative Precipitation in Quatre Soeurs (2005, GSMaP) ...... 4-25 Figure 4.3.15 SWI and Cumulative Precipitation in Quatre Soeurs (2008, GSMaP) ...... 4-25 Figure 4.4.1 Changes in Groundwater Level Triggering Mass Movement while also Affecting Values of Safety Factor Over Time ...... 4-29 Figure 4.4.2 Schematic Diagram of the Modified Fellenius Method ...... 4-34 Figure 4.4.3 Location Map of the Landslide Block in Chitrakoot Area ...... 4-35 Figure 4.4.4 Longitudinal Section for Stability Analysis, Block A in Chitrakoot ...... 4-36 Figure 4.4.5 Longitudinal Section for Stability Analysis, Block B in Chitrakoot ...... 4-36 Figure 4.4.6 C-φ Diagram, Chitrakoot Area ...... 4-39 Figure 4.4.7 Relationship of the Plastic Index and Shear Resistance Angle, the Sliding Surface Clay Gathered at the Position of the Source ...... 4-39 Figure 4.4.8 Location Map of the Landslide Block in Quatre Soeurs Area ...... 4-40 Figure 4.4.9 Longitudinal section for stability analysis, Block A in Quatre Soeurs ...... 4-41 Figure 4.4.10 Longitudinal Section for Stability Analysis, Block B in Quatre Soeurs ...... 4-41 Figure 4.4.11 C-φ Diagram, Quatre Soeurs Area ...... 4-43
ix Figure 4.4.12 Relations of the Plastic Index and Shear Resistance Angle, the Sliding Surface Clay Gathered at the Position of the Source ...... 4-44 Figure 4.4.13 Location Map of the Landslide Block in Vallee Pitot Area ...... 4-45 Figure 4.4.14 Longitudinal Section for Stability Analysis, Block A-2 in Vallee Pitot ...... 4-46 Figure 4.4.15 Longitudinal Section for Stability Analysis, Block E in Vallee Pitot ...... 4-46 Figure 4.4.16 C-φ Diagram, Vallee Pitot Area ...... 4-47 Figure 4.4.17 C-φ Diagram and the Result of Ring Shear Test in Chitrakoot Block-A ...... 4-49 Figure 4.4.18 C-φ Diagram and the Result of Ring Shear Test in Quatre Soeurs Block-A ...... 4-49 Figure 4.4.19 C-φ Diagram and the Result of Ring Shear Test in Vallee Pitot Block-A2 ...... 4-50 Figure 4.5.1 Result of Damaged House Survey, Chitrakoot Area ...... 4-52 Figure 4.5.2 Location of Heavy Damaged House, Quatre Soeurs Area ...... 4-53 Figure 4.5.3 Location of Heavy Damaged House, Vallee Pitot Area ...... 4-54 Figure 5.2.1 Flow Chart of Selection for Landside Countermeasure Work ...... 5-6 Figure 5.2.2 Target Landslide Blocks in Chitrakoot Area ...... 5-7 Figure 5.2.3 Calculation Model for Verification of Effectiveness of the Works -Block A in Chitrakoot Area ...... 5-14 Figure 5.2.4 Calculation Model for Verification of Effectiveness of the Works in Block B in Chitrakoot Area ...... 5-15 Figure 5.2.5 Plan of Countermeasure Works in Chitrakoot Area ...... 5-16 Figure 5.2.6 Plan of Countermeasure Works in Block A ...... 5-17 Figure 5.2.7 Plan of Countermeasure Works in Block B ...... 5-18 Figure 5.2.8 Location Map with Houses of the Landslides ...... 5-20 Figure 5.2.9 Location Map of the Landslides ...... 5-20 Figure 5.2.10 Longitudinal Condition of the Canal ...... 5-21 Figure 5.2.11 Proposed Emergency Works ...... 5-22 Figure 5.2.12 Sand Bags as Counterweights as a Landslide Countermeasure ...... 5-23 Figure 5.3.1 Procedure of EIA Survey ...... 5-28 Figure 6.1.1 Typical Cross Section of Channel for Flood Water ...... 6-2 Figure 6.1.2 Location of the Cross Sections for the Analysis ...... 6-3 Figure 6.1.3 Typical Cross Section of Horizontal Drainage ...... 6-4 Figure 6.1.4 Typical Cross Section of Open-blind Ditch ...... 6-4 Figure 6.1.5 Typical Cross Section of Surface Drainage ...... 6-5 Figure 6.1.6 Typical Cross Section of Upgrade of Existing Water Course ...... 6-6 Figure 6.1.7 Typical Cross section of Protection of the Existing Water Course ...... 6-6 Figure 6.1.8 Location of the Existing Water Course that Often Overflows ...... 6-7 Figure 6.1.9 Typical Drawing of the Drop Structure ...... 6-7 Figure 6.1.10 Typical Cross Section of the Bridge ...... 6-8 Figure 6.1.11 Typical Drawings of Water Catch Basin ...... 6-8 Figure 6.1.12 Location Map of Planned Countermeasure Works in Block A ...... 6-10 Figure 6.1.13 Water Catchment Area for Each Drainage ...... 6-13 Figure 6.1.14 Work Section in Block-A Landslide...... 6-21 Figure 6.1.15 Work Schedule of Work Section I ...... 6-22 Figure 6.1.16 Schedule of the Bidding ...... 6-25 Figure 6.1.17 Flow Chart for Future Plan of Landslide Countermeasure Works in Chitrakoot Area ...... 6-30 Figure 6.1.18 Location of Monitoring Borehole for Block-A Landslide ...... 6-32 Figure 6.1.19 Location of Monitoring Borehole for Block-B Landslide ...... 6-33 Figure 6.2.1 Circulation of the Information ...... 6-38 Figure 6.2.2 Displacements shown in Extensometer Results in Chitrakoot ...... 6-41 Figure 6.2.3 Relation between Rain fall and the Groundwater Level ...... 6-41 Figure 6.2.4 Extensometer Monitoring Results in Chitrakoot and Vallee Pitot ...... 6-42 Figure 6.2.5 Extensometer Monitoring Results in Chitrakoot and Vallee Pitot ...... 6-42 Figure 6.2.6 Extensometer ...... 6-43 Figure 6.2.7 Relation between Time to the Extent of Slope Failure and Velocity of Steady Strain ...... 6-44 Figure 6.2.8 Location Map of Early Warning and Evacuation System in Chitrakoot ...... 6-48 Figure 6.2.9 Location Map of Early Warning and Evacuation System in Vallee Pitot ...... 6-49 Figure.6.2.10 Conception Diagram of Early Warning and Evacuation System ...... 6-49
x Figure 6.2.11 The Parts of the Early Warning and Evacuation System ...... 6-50 Figure.6.2.12 Structure of Siren, Rotary Light ...... 6-51 Figure 6.2.13 Structure of Warning Control Box ...... 6-51 Figure 6.2.14 Structure of Solar Panel ...... 6-51 Figure 6.2.15 Installation of the Early Warning and Evacuation System in Chitrakoot ...... 6-52 Figure 6.2.16 Installation of the Early Warning and Evacuation System in Vallee Pitot ...... 6-52 Figure 7.2.1 Structure of Technical Transfer ...... 7-3 Figure 8.1.1 JICA Environment, Climate Change Adaptation and Disaster Management Program and Related Mauritius Agencies ...... 8-2 Figure 8.3.1 Major Components of IOC Program ...... 8-6 Figure 8.4.1 Relationship between CCD and Related International Organizations/Ministries ...... 8-9 Figure 8.4.2 JICA Climate Change Adaptation/Disaster Management Projects and the Relation with Other International Development Partners, and the Related Policies of Mauritius ...... 8-11 Figure 8.5.1 An Image of Cooperation on Climate Change and Disaster Risk Management among JICA, International Organizations, Mauritius and the Southwest Indian Ocean Islands ...... 8-17 Figure 9.1.1 Outline Image of the Draft Recommendation for Disaster Scheme ...... 9-1 Figure 9.1.2 Outline Image of the Draft Recommendation for PPG ...... 9-2 Figure 9.1.3 The Scope of Application of the Technical Guideline for Initial Survey ...... 9-3 Figure 9.1.4 The Scope of Application of the Procedure Manual for Landslides ...... 9-4 Figure 9.3.1 Flow Chart for Future Plan of Landslide Countermeasure Works in Chitrakoot Area ...... 9-17 Figure 9.3.2 Location of Monitoring Borehole for Block-A Landslide ...... 9-20 Figure 9.3.3 Location of Monitoring Borehole for Block-B Landslide ...... 9-21
xi List of Tables
Page
Table 1.2.1 Overview of Landslide Damage and Countermeasures in Mauritius ...... 1-1 Table 1.4.1 List of JICA Expert Team and Counterparts ...... 1-4 Table 2.3.1 32 Landslide Hazard Areas Selected in the Disasters Scheme ...... 2-5 Table 2.3.2 Revised 37 Landslide Hazard Areas ...... 2-6 Table 2.3.3 Classification of Hazard Area ...... 2-7 Table 2.3.4 Description of the Disaster Type ...... 2-8 Table 2.3.5 Legends of Aerial Photograph Interpretation ...... 2-10 Table 2.3.6 List of Aerial Photographs ...... 2-10 Table 2.3.7 Summary of the Aerial Photograph Interpretation ...... 2-11 Table 2.3.8 The Disaster Focus Points for Landslide Hazard Evaluation ...... 2-12 Table 2.3.9 Description of Scoring Sheet for Evaluating Landslide Hazard ...... 2-13 Table 2.3.10 Result of Landslide Hazard Evaluation ...... 2-13 Table 2.3.11 Landslide Inventory ...... 2-18 Table 2.3.12 Existing GIS Data Collected in Mauritius ...... 2-22 Table 2.3.13 New GIS Data Obtained from Field Surveys, etc...... 2-22 Table 2.4.1 Survey on Structural/Non-structural Measures ...... 2-25 Table 2.4.2 The Structural Countermeasures of Landslide Hazard Area (6 Areas) ...... 2-25 Table 2.4.3 Current Condition of Landslide Monitoring in Mauritius ...... 2-27 Table 2.5.1 Land Use Changes as Per Category in Mauritius During the Period 1986 to 2010 ...... 2-29 Table 2.5.2 Water Utilization ...... 2-33 Table 2.5.3 Summary of Attitude Survey about Landslide Disasters ...... 2-34 Table 2.5.4 Items and Content of the Survey Sheet ...... 2-35 Table 2.5.5 Summary of Simple Tabulation Results of All Respondents ...... 2-36 Table 2.5.6 Comparison of Awareness in the Three Pilot Sites ...... 2-37 Table 2.6.1 Main Authorities of Disaster Management ...... 2-39 Table 2.6.2 Main Ministries and Organizations in Charge of Landslide Disaster Management ... 2-41 Table 2.6.3 Main Ministries and Organizations in Charge of Landslide Disaster Management for Ordinary and Emergency Situations ...... 2-42 Table 2.7.1 GDP, GDP Per Capita and GDP Growth ...... 2-43 Table 2.7.2 Budget for the MPI ...... 2-48 Table 2.7.3 Budget for the LMU from 2015 to 2017 ...... 2-49 Table 3.1.1 Results of Landslide Hazard Area Selection ...... 3-2 Table 3.2.1 Table of Quantities of Survey Areas ...... 3-3 Table 3.3.1 Outline of Stratum ...... 3-9 Table 3.3.2 Features of Stratum ...... 3-11 Table 3.3.3 Application for Soil Strength and Mechanical Property Test ...... 3-12 Table 3.3.4 Selection of Test Method for Type of Sample and Characteristics of Strength Obtained by Test ...... 3-15 Table 3.3.5 Previous Survey Report ...... 3-19 Table 3.3.6 List of Laboratory Soil Tests Conducted ...... 3-19 Table 3.3.7 Results of Physical Test ...... 3-20 Table 3.3.8 Results of Physical Test ...... 3-20 Table 3.3.9 Results of Shear Box Test ...... 3-21 Table 3.3.10 Results of Triaxial Compression ...... 3-21 Table 3.3.11 Results of Physical Test ...... 3-21 Table 3.3.12 Results of Physical Test ...... 3-22 Table 3.3.13 Results of Triaxial Compression ...... 3-22 Table 3.3.14 List of Laboratory Soil Tests ...... 3-22 Table 3.3.15 Results of Physical Test(1) ...... 3-23 Table 3.3.16 Results of Physical Test(2) ...... 3-23 Table 3.3.17 Results of Physical Test (1) ...... 3-24 Table 3.3.18 Results of Physical Test (2) ...... 3-24 Table 3.3.19 Ring Shear Test Result...... 3-30
xii Table 3.3.20 Status of Sampling for Water Quality Testing ...... 3-31 Table 3.3.21 Water Quality Test Method ...... 3-31 Table 3.4.1 Instruments for the Landslide Monitoring ...... 3-35 Table 3.4.2 Monthly and Maximum Daily Precipitation and Maximum Hourly Precipitation ...... 3-38 Table 3.4.3 Monthly Precipitation, The Maximum Daily Precipitation and The Maximum Hourly Precipitation ...... 3-44 Table 3.5.1 Specifications of the Seismic Exploration ...... 3-50 Table 3.5.2 Extent & Specifications of the Seismic Exploration ...... 3-50 Table 3.5.3 List of Equipment to be Used ...... 3-52 Table 3.5.4 Comparison between Peel Off and Tomographic Methods ...... 3-54 Table 3.5.5 Summary Table of the Various Strata Identified ...... 3-56 Table 3.5.6 Specifications of Two-dimensional Resistivity Exploration ...... 3-59 Table 3.5.7 Extent & Specifications of the Resistivity Exploration ...... 3-59 Table 3.5.8 Summary Table of the Various Strata Identified ...... 3-64 Table 3.6.1 Field Drilling Schedule (Chitrakoot) ...... 3-68 Table 3.6.2 Field Drilling Schedule (Quatre Soeurs) ...... 3-68 Table 3.6.3 Borehole Details ...... 3-69 Table 3.6.4 Borehole Details ...... 3-70 Table 3.6.5 Specifications of the Drilling Machines and Materials ...... 3-70 Table 3.6.6 Rock Mass Weathering ...... 3-72 Table 3.6.7 Quality Classification of Rocks by RQD Values ...... 3-72 Table 3.6.8 Strength Description of Rock Material ...... 3-72 Table 3.6.9 Classification of Discontinuity Spacing ...... 3-73 Table 3.6.10 Specifications of the Pipe Strain Gauge ...... 3-74 Table 3.6.11 Specifications of the Special Casing Pipe (Guide Pipe) ...... 3-75 Table 3.6.12 Specifications of the Piezometer ...... 3-77 Table 3.6.13 Standard Penetration Test ...... 3-78 Table 3.6.14 Relationship between Strata Classification and Geological Features ...... 3-78 Table 3.6.15 Standard Penetration Test ...... 3-79 Table 3.6.16 Relationship between Strata Classification and Geological Features ...... 3-79 Table 3.6.17 Soil Strength Description ...... 3-79 Table 3.6.18 Standard Penetration Test ...... 3-80 Table 3.6.19 Standard Penetration Test ...... 3-81 Table 3.7.1 Differentiation of House Deformations and Causes of Damage ...... 3-84 Table 3.7.2 Monitoring of Damaged Houses ...... 3-85 Table 3.7.3 Areas with Extensive Damage and Its Characteristics ...... 3-89 Table 3.7.4 The Characteristics of Slope Classification ...... 3-104 Table 3.8.1 The 37 Slope Disaster Hazard Areas in the Disasters Scheme ...... 3-120 Table 3.8.2 The Results of Disaster Inspection for 37 Slope Disaster Areas ...... 3-123 Table 3.9.1 The Warning Stages, Standards for Issuing Warnings and Responses ...... 3-128 Table 3.9.2 Existing Situation, Issues and Basic Policy for Countermeasure regarding the Warning/Evacuation System in the Disaster Scheme ...... 3-132 Table 3.9.3 Existing Disaster Scheme Article, Draft Proposal of Addition/Modification, Reason of Addition/Modification and Necessity ...... 3-133 Table 3.9.4 Record of the Meeting/Workshop regarding the Recommendation ...... 3-147 Table 3.9.5 Points to Remember for the Recommendations ...... 3-148 Table 3.10.1 Summary of the Landslide Disasters Prevention Act ...... 3-155 Table 3.10.2 Related Acts regarding Landslide Disaster Prevention ...... 3-156 Table 3.10.3 The Existing Mauritian Legal Systems/Schemes for LDRM ...... 3-157 Table 3.10.4 Interview Survey Results relating to Development Restrictions in Chitrakoot ...... 3-160 Table 3.10.5 Interview Survey Result about the Development Restrictions in Quatre Soeurs .... 3-163 Table 3.10.6 Existing PPG Article, Draft Proposal of Addition/Modification, Reason of Addition/Modification and Necessity ...... 3-168 Table 3.10.7 Supplementary Recommendation for Flexible Review of Permitted Area of Development ...... 3-173 Table 3.10.8 Supplementary Recommendation for the Education/Dissemination and Capacity Development ...... 3-174 Table 3.10.9 Record of the Meeting/Workshop regarding the Recommendation ...... 3-175
xiii Table 3.10.10 Points to Remember for the Recommendations ...... 3-177 Table 3.11.1 The Contents of the Technical Guideline for Initial Survey ...... 3-180 Table 3.12.1 The Contents of the Procedure Manual for Landslides ...... 3-182 Table 4.3.1 Parameters of Tank Model ...... 4-15 Table 4.3.2 Summary of GSMaP Data ...... 4-17 Table 4.3.3 Sediment Disaster Record at Chitrakoot ...... 4-19 Table 4.3.4 SWI and MMS Cumulative Precipitation for Rainfall Event ①~⑫ ...... 4-20 Table 4.3.5 SWI and GSMaP Cumulative Precipitation for Rainfall Event ⑬~⑳ ...... 4-22 Table 4.3.6 Sediment Disaster Record at Quatre Souers ...... 4-23 Table 4.3.7 SWI and MMS Cumulative Precipitation for Rainfall Event ㉑~㉚ ...... 4-24 Table 4.3.8 SWI and GSMaP Cumulative Precipitation for Rainfall Event ㉛~㉟ ...... 4-25 Table 4.3.9 SWI with Landslide Risk at Chitrakoot and Quatre Soeurs ...... 4-26 Table 4.4.1 Definition of Safety Factor for Landslide ...... 4-29 Table 4.4.2 Landslide Slope Stability Methods and Selected Factors ...... 4-31 Table 4.4.3 Definition of Safety Factor for Landslide ...... 4-33 Table 4.4.4 Current Factor of Safety of the Landslide, Chitrakoot Area ...... 4-37 Table 4.4.5 Result of the Laboratory Soil Test, Chitrakoot area ...... 4-37 Table 4.4.6 Existing Result of the Laboratory Soil Test, La Butte Landslide ...... 4-37 Table 4.4.7 Result of the Stability Analysis, Chitrakoot Area ...... 4-39 Table 4.4.8 Current Factor of Safety of the Landslide, Quatre Soeurs Area ...... 4-41 Table 4.4.9 Result of the Laboratory Soil Test, Quatre Soeurs Area ...... 4-42 Table 4.4.10 Result of the Stability Analysis, Quatre Soeurs Area ...... 4-43 Table 4.4.11 Current Factor of Safety of the Landslide, Vallee Pitot Area ...... 4-46 Table 4.4.12 Result of the Stability Analysis, Vallee Pitot Area ...... 4-47 Table 4.4.13 Results of Ring Shear Test, Cohesion C and Shear Resistance Angle φ ...... 4-48 Table 4.5.1 Susceptibility Assessment Items ...... 4-51 Table 4.5.2 Results of Susceptibility Assessment in Chitrakoot Area ...... 4-51 Table 4.5.3 Results of Susceptibility Assessment in Quatre Soeurs Area ...... 4-52 Table 4.5.4 Results of Susceptibility Assessment in Vallee Pitot Area ...... 4-54 Table 5.1.1 Items Considered for Selection of Pilot Project Site ...... 5-1 Table 5.2.1 Selection of Target Landslide Block in Chitrakoot Area ...... 5-8 Table 5.2.2 Selection of Control Work for Chitrakoot Area ...... 5-9 Table 5.2.3 Comparative Chart of Control Work Selection in Chitrakoot Area ...... 5-12 Table 5.2.4 Result of Consideration of Effectiveness of Countermeasure Works ...... 5-16 Table 5.2.5 Proposed Schedule for the Countermeasures ...... 5-22 Table 5.2.6 Background and Progress of the Relocation of the Inhabitants of Quatre Soeurs ...... 5-24 Table 5.3.1 Undertaking Requiring PER and EIA ...... 5-26 Table 5.3.2 Expected Environmental and Social Consideration and Impact Items and Mitigation Measures ...... 5-29 Table 5.4.1 General Sheet of the Pilot Project ...... 5-30 Table 5.4.2 Check Sheet of Pre Evaluation in the Pilot Project ...... 5-31 Table 5.4.3 Check Sheet of Interim Review in the Pilot Project ...... 5-33 Table 5.4.4 Check Sheet of Post Evaluation in the Pilot Project ...... 5-34 Table 5.5.1 Breakdown of Budget in 2013 ...... 5-36 Table 5.5.2 List of Countermeasures and Budgets in 2014-2016 ...... 5-37 Table 5.5.3 List of Countermeasures and Budgets in 2015-2017 ...... 5-38 Table 5.6.1 Organizational Structure of MPI and Civil Engineering Section ...... 5-42 Table 5.6.2 Organizational Structure of MPI and Civil Engineering Section ...... 5-42 Table 5.6.3 Issues, Goals and Activities in Capacity Development Plan ...... 5-44 Table 5.6.4 Full-time Staff Assignment (Long Term Goal) ...... 5-48 Table 5.6.5 Budget for the LMU from 2015 to 2017 ...... 5-48 Table 5.6.6 Main Responsible Organizations based on Disaster Classification, Objects of Protection and the Scale of Protection ...... 5-50 Table 5.6.7 Task Flow for Emergency Situation for All Sites ...... 5-52 Table 5.6.8 Emergency Operational System within the LMU ...... 5-53 Table 6.1.1 Classification of Landslide Countermeasure Works ...... 6-1 Table 6.1.2 Condition of Stability Analysis of Slope behind the Channel for Flood Water ...... 6-3
xiv Table 6.1.3 Result of the Stability Analysis of the Slope behind the Channel ...... 6-3 Table 6.1.4 Countermeasure Works (Control Work) for the Block-A Landslide ...... 6-9 Table 6.1.5 Runoff Coefficient based on Ground Surface Condition, ...... 6-11 Table 6.1.6 Intensity of Rainfall ...... 6-12 Table 6.1.7 Water Catchment Area for Each Drainage ...... 6-12 Table 6.1.8 Condition and Result of the Calculation of Runoff Volume ...... 6-13 Table 6.1.9 Manning's Roughness Coefficient, ...... 6-14 Table 6.1.10 Condition and Result of Calculation of Discharge Volume of Each Horizontal Drainage Pipe ...... 6-15 Table 6.1.11 Design Discharge Volume of Each Horizontal Drainage Work ...... 6-15 Table 6.1.12 Condition and Result of the Calculation for the Discharge Capacity of Each Designed Drainage ...... 6-16 Table 6.1.13 Evaluation Result of the Availability of Designed Drainages ...... 6-16 Table 6.1.14 Plan of Access Road for the Construction Work ...... 6-17 Table 6.1.15 Quantity Survey Result for Countermeasure Works for Block-A Landslide in Chitrakoot Area ...... 6-18 Table 6.1.16 Quantity and Cost Estimation of Countermeasure Works in Chitrakoot Area ...... 6-19 Table 6.1.17 Major Machinery and Materials for the Works ...... 6-22 Table 6.1.18 Outline of the Landslide Countermeasure Works ...... 6-23 Table 6.1.19 Long List of Local Contractors ...... 6-24 Table 6.1.20 List of Local Contractors Participated in the Site Explanation ...... 6-26 Table 6.1.21 List of Local Contractor Participants in the Opening of Bid ...... 6-26 Table 6.1.22 Result of Bidding Price and Selected Bidder ...... 6-28 Table 6.1.23 List of Changed Design Part ...... 6-29 Table 6.1.24 Planned Landslide Countermeasure Works in Chitrakoot Area ...... 6-31 Table 6.1.25 Reference Value of the Groundwater Level to Achieve the Planned Factor of Safety ...... 6-32 Table 6.1.26 Reference Value of the Groundwater Level to Achieve the Planned Factor of Safety ...... 6-33 Table 6.1.27 Available Countermeasure Work in Mauritius ...... 6-34 Table 6.1.28 Advisability of the Development Activities in the Landslide Hazard Zone ...... 6-35 Table 6.2.1 Five Stages in Landslide Emergency Scheme ...... 6-37 Table 6.2.2 Proposed Early Warning of Landslide Disaster ...... 6-39 Table 6.2.3 Proposed Thresholds ...... 6-44 Table 6.2.4 Estimation of Velocity of Displacement in Accordance with Time to the Extent of Failure ...... 6-45 Table 6.2.5 Proposed Threshold ...... 6-45 Table 6.2.6 Proposed Early Warning of Landslide Disaster in Chitrakoot, Vallee Pitot and Quatre Soeurs ...... 6-47 Table 6.2.7 Specifications of the Alarm Operation ...... 6-48 Table 6.2.8 Quantity of Parts ...... 6-50 Table 6.3.1 IEC Category ...... 6-53 Table 6.3.2 Current Status and Issues of IEC Activity in the Field of Landslide Management in Mauritius / IEC Activities to be Implemented to Address Issues Identified ...... 6-54 Table 6.3.3 IEC Activities Described in Mauritius Landslide Emergency Scheme (2012-2013).... 6-55 Table 6.3.4 IEC Activities to be Implemented by the Project...... 6-56 Table 6.3.5 Implementation Plan of Stakeholder Meeting ...... 6-58 Table 6.3.6 Reports of Results of Stakeholder Meetings at Priority Areas...... 6-60 Table 7.1.1 Objectives and Inputs on Technical Transfer ...... 7-1 Table 7.1.2 Each Development Stage of the CD ...... 7-2 Table 7.2.1 The JICA Expert Team Members by Group of Expertise ...... 7-3 Table 7.4.1 Summary of Landslide Workshop ...... 7-7 Table 7.4.2 Outline of “Fundamentals and Basics on Landslides” ...... 7-7 Table 7.4.3 Outline of “Landslide Reconnaissance” ...... 7-8 Table 7.4.4 Outline of “Monitoring Device” ...... 7-9 Table 7.4.5 Outline of “Land Use Policy for Landslide Disaster” ...... 7-9 Table 7.4.6 Outline of “Interpretation of Aerial Photo for Landslide” ...... 7-10 Table 7.4.7 Outline of “Landslide Investigation/Analysis/Monitoring” ...... 7-11
xv Table 7.4.8 Outline of “Geotechnical Site Characterization and Constant Volume Direct Shear Test” ...... 7-11 Table 7.4.9 Outline of “Training of the Landslide Monitoring” ...... 7-12 Table 7.4.10 Outline of “Monitoring Result and Early Warning” ...... 7-13 Table 7.4.11 Outline of “Review of Planning Policy Guidance” ...... 7-13 Table 7.4.12 Outline of “Stability Analysis and Countermeasures” ...... 7-14 Table 7.4.13 Outline of “Monitoring Log for Pilot Site” ...... 7-14 Table 7.4.14 Outline of “Countermeasure Works 1” ...... 7-15 Table 7.5.1 Contents of Training in Japan ...... 7-16 Table 7.5.2 Schedule of the 1st Training in Japan in 2012 ...... 7-17 Table 7.5.3 Schedule of the 2nd Training in Japan in 2013 ...... 7-18 Table 7.6.1 Plan of SC ...... 7-21 Table 7.6.2 The Contents of the 1st SC ...... 7-21 Table 7.6.3 The Contents of the 2nd SC ...... 7-22 Table 7.6.4 The Contents of the 3rd SC ...... 7-23 Table 7.6.5 The Contents of the 4th SC ...... 7-24 Table 7.7.1 Schedule of Contents to Deliberate in the Advisory Committee ...... 7-26 Table 7.7.2 Contents of 1st Advisory Committee in Japan ...... 7-26 Table 7.7.3 Contents of 2nd Advisory Committee in Japan ...... 7-27 Table 7.7.4 Contents of 3rd Advisory Committee in Japan ...... 7-27 Table 7.7.5 Contents of 4th Advisory Committee in Japan ...... 7-28 Table 7.8.1 Technical Contents to be Transferred to C/P ...... 7-29 Table 7.8.2 Contents of the Project in 2012-2015 ...... 7-30 Table 7.8.3 Classification of Hazard Areas on the Disaster Scheme ...... 7-31 Table 7.9.1 Main Responsible Organizations based on Disaster Classification, Objects of Protection and the Scale of Protection ...... 7-35 Table 7.9.2 Task Flow for Emergency Situation for All Sites ...... 7-36 Table 7.9.3 Emergency Operational System within the LMU ...... 7-37 Table 8.3.1 Relevant Programs of Major Development Partners ...... 8-6 Table 8.3.2 Contents of DRR ...... 8-7 Table 8.5.1 Presentation Details ...... 8-14 Table 8.5.2 Discussion Details ...... 8-15 Table 8.5.3 Participant List for the Day 1 ...... 8-17 Table 9.1.1 The Contents of the Technical Guideline for Initial Survey ...... 9-4 Table 9.1.2 The Contents of the Procedure Manual for Landslides ...... 9-5 Table 9.2.1 Breakdown of Budget in 2013 ...... 9-6 Table 9.2.2 List of Countermeasures and Budgets in 2014-2016 ...... 9-7 Table 9.2.3 List of Countermeasures and Budgets in 2015-2017 ...... 9-8 Table 9.2.4 Full-time Staff Assignment (Long Term Goal) ...... 9-11 Table 9.2.5 Main Responsible Organizations based on Disaster Classification, Objects of Protection and the Scale of Protection ...... 9-12 Table 9.2.6 Task Flow for Emergency Situation for All Sites ...... 9-14 Table 9.2.7 Emergency Operational System within the LMU ...... 9-15 Table 9.3.1 Planned Landslide Countermeasure Works in Chitrakoot Area ...... 9-18 Table 9.3.2 Reference Value of the Groundwater Level to Achieve the Planned Factor of Safety ...... 9-19 Table 9.3.3 Reference Value of the Groundwater Level to Achieve the Planned Factor of Safety ...... 9-21 Table 9.3.4 Advisability of the Development Activities in the Landslide Hazard Zone ...... 9-23 Table 9.3.5 Proposed Early Warning of Landslide Disaster ...... 9-24 Table 9.4.1 Classification of Hazard Areas ...... 9-27 Table 9.4.2 Hazard Evaluation Results of the 6 Landslides ...... 9-27
xvi
List of Photos
Page: Photo 2.3.1 Aerial Photograph Interpretation ...... 2-9 Photo 3.3.1 Full View of Landslide Area ...... 3-7 Photo 3.3.2 Scarp in Landslide Area...... 3-8 Photo 3.3.3 Active Area of Landslide ...... 3-8 Photo 3.3.4 Full View of Landslide Area ...... 3-10 Photo 3.3.5 Road at the Toe of The Landslide ...... 3-10 Photo 3.3.6 Sampling Situation ...... 3-27 Photo 3.3.7 Samples ...... 3-27 Photo 3.6.1 The Drilling Machines and Materials ...... 3-71 Photo 3.6.2 Installation of the Pipe Strain Gauge ...... 3-74 Photo 3.6.3 Installation of the Casing Pipe (Guide Pipe) ...... 3-76 Photo 3.6.4 Installation of Water Level Meter ...... 3-77 Photo 3.7.1 Cracks in House 1 ...... 3-86 Photo 3.7.2 Cracks in House 2 ...... 3-86 Photo 3.7.3 Cracks in Houses 3,4,5 ...... 3-87 Photo 3.7.4 Cracks in House19 ...... 3-87 Photo 3.7.5 Steps to the School Building Foundation (East Side) ...... 3-90 Photo 3.7.6 Floor of the School Building Foundation (West Side) ...... 3-90 Photo 3.7.7 Major Damage to the Steps ...... 3-90 Photo 3.7.8 Intermittent Cracks (East-West) ...... 3-90 Photo 3.7.9 Vertical Displacement beside Extensometer(5) ...... 3-91 Photo 3.7.10 Direction of Vertical Displacement (East-West) ...... 3-91 Photo 3.7.11 Damage to the Retaining Wall (Roadside) ...... 3-91 Photo 3.7.12 Settling of the Roadside Ditch ...... 3-91 Photo 3.7.13 Lavatory beside School (House No.9) ...... 3-91 Photo 3.7.14 An Elementary School in Chitrakoot (House No.18) ...... 3-92 Photo 3.7.15 Cracks in the School Wall ...... 3-92 Photo 3.7.16 Cracks in the Base of the Wall ...... 3-92 Photo 3.7.17 Cracks in the corner of the School Building ...... 3-92 Photo 3.7.18 The Wall and Sidewalk facing Main Road ...... 3-92 Photo 3.7.19 Heavily Damaged House ...... 3-93 Photo 3.7.20 Heavily Damaged House ...... 3-93 Photo 3.7.21 Gaps and Unevenness in the Curb ...... 3-93 Photo 3.7.22 Cracks in the Retaining Wall of the House in front of the School ...... 3-93 Photo 3.7.23 Cracks in the Retaining Wall beside House ...... 3-94 Photo 3.7.24 Cracks in the Veranda ...... 3-94 Photo 3.7.25 Deformation of the House in front of the School ...... 3-94 Photo 3.7.26 Deformation of the Concrete Foundation of Suspected House Remains ...... 3-95 Photo 3.7.27 Cracks in the Concrete Structure ...... 3-95 Photo 3.7.28 Cracks in the Floor ...... 3-95 Photo 3.7.29 Settling in the Middle of House ...... 3-96 Photo 3.7.30 Cracks in the Wall (Window Frame) ...... 3-96 Photo 3.7.31 Inclination of the House (Left: Settling) ...... 3-96 Photo 3.7.32 Penetrating Cracks in the Wall ...... 3-96 Photo 3.7.33 Road that Leads Down to Houses (Extensometer is Installed up ahead) ...... 3-96 Photo 3.7.34 Extensometer E(1) (Shot from below) ...... 3-97 Photo 3.7.35 Deformation of the Protection Fence Foundation Concrete ...... 3-97 Photo 3.7.36 Cracks in the House Wall ...... 3-97 Photo 3.7.37 Horizontal Open Cracks ...... 3-97 Photo 3.7.38 Extensometer E(2) (Shot from below) ...... 3-98 Photo 3.7.39 Deformation of the Protection Fence foundation ...... 3-98 Photo 3.7.40 Surrounding Slopes of Extensometer E(2) ...... 3-98 Photo 3.7.41 Surrounding slopes of Extensometer E(2) ...... 3-99
xvii Photo 3.7.42 Farmland between Extensometer E(1) and Stream ...... 3-99 Photo 3.7.43 Advancement of Bank Erosion (Downstream) ...... 3-99 Photo 3.7.44 Advancement of Bank Erosion (Upstream) ...... 3-100 Photo 3.7.45 Heavily Damaged House ...... 3-100 Photo 3.7.46 Open Cracks in the House and Retaining Wall ...... 3-100 Photo 3.7.47 Cracks in the Road ...... 3-101 Photo 3.7.48 Road in front of House ...... 3-101 Photo 3.7.49 Sugarcane Field in front of House ...... 3-101 Photo 3.7.50 Sugarcane Field (Shot from below) ...... 3-101 Photo 3.7.51 House No.40 ...... 3-102 Photo 3.7.52 Penetrating Cracks in the Wall ...... 3-102 Photo 3.7.53 House No.41 ...... 3-103 Photo 3.7.54 Cavity in the Concrete Foundation ...... 3-103 Photo 3.7.55 Cracks in the Wall ...... 3-103 Photo 3.7.56 Cracks in the Wall (Entrance) ...... 3-103 Photo 3.7.57 Full View of the Site ...... 3-104 Photo 3.7.58 Upper Slope (Shot from below, Gradient:16～20°) ...... 3-105 Photo 3.7.59 Middle Slope (Shot from below, Gradient:5°) ...... 3-105 Photo 3.7.60 Lower Slope (Shot from below, Gradient:15～17°) ...... 3-105 Photo 3.7.61 Full View of the Upper Slope ...... 3-106 Photo 3.7.62 Vicinity of the Slope (Elevation: about 50m) ...... 3-106 Photo 3.7.63 Vicinity of the Slope (Elevation: about 70m) ...... 3-106 Photo 3.7.64 Outcrop (Elevation: about 80m) ...... 3-106 Photo 3.7.65 Past Deformations on Upper Slope (From Past Report) ...... 3-107 Photo 3.7.66 Deformations around Borehole BH-1 (Current Condition) ...... 3-107 Photo 3.7.67 Deformations around Elevation 45m (Current Condition) ...... 3-107 Photo 3.7.68 Cracks in the Farm Road ...... 3-107 Photo 3.7.69 Cracks in the Farm Road ...... 3-107 Photo 3.7.70 Cracks along the Farm Road ...... 3-108 Photo 3.7.71 Marshy Land ...... 3-108 Photo 3.7.72 Full View from Borehole BH-1 ...... 3-109 Photo 3.7.73 Collapse at the Head of a Stream ...... 3-109 Photo 3.7.74 Road above the Houses ...... 3-110 Photo 3.7.75 Cracks in the Road ...... 3-110 Photo 3.7.76 View of the end of the Road (East Side Slope) ...... 3-110 Photo 3.7.77 View of the Starting Point ...... 3-111 Photo 3.7.78 Opening between Road and Boundary Line ...... 3-111 Photo 3.7.79 Horizontal Open Cracks in the Wall ...... 3-111 Photo 3.7.80 Open Cracks in the Foundation ...... 3-111 Photo 3.7.81 Middle of the Slope ...... 3-112 Photo 3.7.82 Slope above House19 ...... 3-112 Photo 3.7.83 Masonry Retaining Wall behind House 19 ...... 3-112 Photo 3.7.84 Steps on the Lower Slope ...... 3-113 Photo 3.7.85 Swelling on the Road ...... 3-113 Photo 3.7.86 Cracks in the Concrete Wall ...... 3-113 Photo 3.7.87 Masonry Retaining Wall in front of the Road ...... 3-114 Photo 3.7.88 View of the Ocean Side from House 19 ...... 3-114 Photo 3.7.89 Damage to House (1) ...... 3-115 Photo 3.7.90 Main Scalp and Landslide Toe ...... 3-116 Photo 3.7.91 Damage to House(2) ...... 3-116 Photo 3.7.92 Landslide Plan Map, 2nd Reconnaissance at, 22nd February 2013 ...... 3-117 Photo 3.7.93 Damage on the Outer Wall of House(1), Large Open Crack Grew ...... 3-117 Photo 3.7.94 House (1) was Tilting as Result of Landslide Activity, Causing a Large Gap with the Neighboring House ...... 3-117 Photo 3.7.95 Open crack in the room of House (1) ...... 3-118 Photo 3.7.96 The cracks and steps in the room of House (1) ...... 3-118 Photo 3.7.97 The Outside Wall of House (1) was Completely Broken ...... 3-118
xviii Photo 3.7.98 New Open Cracks in the Upper Part of House (1) ...... 3-118 Photo 3.10.1 Sprawl to Slope Area in Vallée Pitot ...... 3-165 Photo 5.2.1 Upper Side of the Blockage of the Canal ...... 5-18 Photo 5.2.2 Lower Side of the Blockage of the Canal ...... 5-18 Photo 5.2.3 Seen below the Blockage ...... 5-19 Photo 5.2.4 Seen above the Blockage ...... 5-19 Photo 6.3.1 Scenes of Interview Survey ...... 6-67 Photo 6.3.2 Handbook ...... 6-70 Photo 6.3.3 Awareness Activity for Residents Using the Handbook (Chitrakoot) ...... 6-70 Photo 7.3.1 1st Technical Transfer Seminar ...... 7-4 Photo 7.3.2 2nd Technical Transfer Seminar ...... 7-5 Photo 7.3.3 3rd Technical Transfer Seminar ...... 7-6 Photo 7.4.1 Photo of “Fundamentals and Basics on Landslides” ...... 7-8 Photo 7.4.2 Photo of “Landslide Reconnaissance” ...... 7-8 Photo 7.4.3 Photo of “Monitoring device” ...... 7-9 Photo 7.4.4 Photo of “Land Use Policy for Landslide Disaster” ...... 7-10 Photo 7.4.5 Photo of “Interpretation of Aerial Photo for Landslide” ...... 7-10 Photo 7.4.6 Photo of “Landslide Investigation/Analysis/Monitoring” ...... 7-11 Photo 7.4.7 Photo of “Geotechnical Site Characterization and Constant Volume Direct Shear Test” ...... 7-12 Photo 7.4.8 Photo of “Training of the Landslide Monitoring” ...... 7-12 Photo 7.4.9 Photo of “Monitoring Result and Early Warning” ...... 7-13 Photo 7.4.10 Photo of “Review of Planning Policy Guidance” ...... 7-14 Photo 7.4.11 Photo of “Stability Analysis and Countermeasures” ...... 7-14 Photo 7.4.12 Photo of “Monitoring log for Pilot Site” ...... 7-15 Photo 7.4.13 Photo of “Countermeasure Works 1” ...... 7-15 Photo 7.5.1 The 2nd Training in Japan in 2013 ...... 7-20 Photo8.5.1 Participants of the Seminar (5th March 2015) ...... 8-13 Photo8.5.2 Presentation by the Neighbouring Islands (5th March 2015) ...... 8-13 Photo8.5.3 Explaining the Monitoring System and Countermeasure Works in Chitrakoot (6th March 2015) ...... 8-15 Photo8.5.4 Group Photo taken at Grand Sable (6th March 2015) ...... 8-15
xix
Abbreviations
Abbreviation English AAP Africa Adaptation Programme AC Advisory Committee AF Adaptation Fund AFD Agence Française de Développement AFP Adaptation Fund Programme BA Building Act BLUPG The Building and Land Use Permit Guide CCIC Climate Change Information Center C/P Counterpart CA Capacity Assessment CADMAC Climate Change Adaptation and Disaster Management Committee CC Crisis Committee CCD Climate Change Division CD Capacity Development CD Consolidated Drained test CDEMA Caribbean Disaster Emergency Management Agency CEB The Central Electricity Board CONDC The Cyclone and Other Natural Disasters Committee CONDS Cyclone and Other Natural Disasters Scheme CSO Central Statistics Office CU (CU-bar) Consolidated Undrained test CWA The Central Water Authority DEM Digital Elevation Model DRR Disaster Risk Reduction EU European Union F/S Feasibility Study FAS First Aid Service Fs Safety Factor/Factor of Safety GDP Gross Domestic Product GIS Government Information Service GIS Geographic Information System GL Ground Level GSMaP Global Satellite Mapping of Precipitation HFA Hyogo Framework for Action IC/R Inception Report ICZM Integrated Coastal Zone Management IEC Information, Education, and Communication IOC(COI) Indian Ocean Commission (Commission de l'Océan Indien) IP Plasticity Index/(Index of Plasticity) ISO International Organization for Standardization JET JICA Expert Team JICA Japan International Cooperation Agency
xx JICE Japan International Corporation Center LDRM Landslide Disaster Risk Management LGA Local Government Act, 2003 LL Liquid Limit LMU Landslide Management Unit M/M Minutes of Meeting Mauritius The Republic of Mauritius MBC Mauritius Broadcasting Corporation MEHR Ministry of Education and Human Resources Ministry of Environment, Sustainable Development, Disaster and Beach MESDDBM Management MGCW Ministry of Gender Equality, Child Development and Family Welfare MHL Ministry of Housing and Lands MHQL Ministry of Health and Quality of Life MID Maurice Ile Durable MLG Ministry of Local Government & Outer Islands MoESD Ministry of Environment and Sustainable Development MoFED Ministry of Finance and Economic Development MPI Ministry of Public Infrastructure and Land Transport MMS Mauritius Meteorological Services MSS Ministry of Social Security, National Solidarity and Reform Institutions MTEF Medium-Term Expenditure Framework MTL Ministry of Tourism and Leisure MTSRT Ministry of Tertiary Education, Science, Research and Technology NDOCC National Disaster and Operations Coordination Centre NDRMCC National Disaster Risk Reduction and Management Center NDS National Development Strategy NDU National Development Unit NGO Non-Governmental Organization ODA Official Development Assistance OPS Outline Planning Schemes P.Fs Planning/Designed Factor of Safety P/R Progress Report PBB Programme-Based Budgeting PDA Planning and Development Act PEFA Public Expenditure and Financial Accountability PFM Public Financial Management PIU Planning and Implementation Units PL Plastic Limit PMO Prime Minister’s Office PMS Performance Management System PPG Planning Policy Guidance PS Permanent Secretary PVC Polyvinyl Chloride R/D Record of Discussion RRU Repair and Rehabilitation Unit SC Steering Committee
xxi SIDS Small Island Developing States SPT Standard Penetration Test SWI Soil Water Index TAS Treasury Accounting System TCPA Town and Country Planning Act The Disasters Scheme The Cyclone and Other Natural Disasters Scheme The Project The Project of Landslide Management in the Republic of Mauritius TICAD IV The Fourth Tokyo International Conference on African Development TRMM Tropical Rainfall Measuring Mission UNDP The United Nations Development Programme WCDR World Conference on Disaster Reduction
xxii JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC.
Digest This report is a Final Report (hereinafter F/R) which covers the results of all activities for the Project of Landslide Management in the Republic of Mauritius (hereinafter the Project) according to the Record of Discussion (hereinafter R/D) agreed upon between the Ministry of Public Infrastructure and Land Transport (hereinafter MPI), of the Republic of Mauritius (hereinafter Mauritius) and the Japan International Cooperation Agency (hereinafter JICA).
As for the introduction in Chapter 1, the background/outcomes/scope/schedule of the Project and the main activities are described.
JICA has dispatched 14 experts (hereinafter JET, or JICA Expert Team) who specialize in investigation, analysis, design and countermeasures of landslides. The Project is conducted with members of the Repair and Rehabilitation Unit/ Landslide Management Unit (hereinafter RRU/LMU) in MPI as Counterparts (hereinafter the C/P) from May 2012 to March 2015.
The objectives of the Project are; 1) Formulation of a landslide management plan to establish a landslide monitoring system, 2) Implementation of the F/S and pilot project to examine, carry out and learn specific approaches, 3) Improvement of landslide management skills at RRU/LMU and other related institutions.
For the basic survey in Chapter 2, the topography, the geology, landslide inventory, existing countermeasures, social survey, organizations and systems and economic survey on the entire Mauritius area are described.
Mauritius is a volcanic island with a volcanic plateau of 300 - 400m formed by these craters. The island consists of basaltic flows and the geological history began approximately 10 million years ago and there were two cycles of volcanic activity involved in the formation of the island. The average annual rainfall amount is about 2,000mm and almost 70% is concentrated during the rainy season (December - May). Many large-scale cyclones occur during the rainy season, causing most of the landslide disasters to occur during this season.
Reconnaissance has been conducted for the 32 landslide hazard areas selected in the "Cyclone and Other Natural Disasters Scheme 2011-2012 (hereinafter the Disaster Scheme)" and several of the 32 landslide hazard areas were divided, bringing the total to 37 areas. The 37 hazard areas are classified into nine (9) kinds of disasters: landslide, slope failure, rock fall, debris flow, stream erosion, damage of embankment, wall damage, house damage, and land subsidence (cave-in). A landslide inventory and a hazard evaluation have been implemented for the 37 areas based on aerial photo interpretation, site survey and checking for existing countermeasures.
Social condition such as land use, population, poverty and water resource and economical condition such as economic indices (GDP, etc.), economic policy and budget have been organized. The questionnaire for 300 households has revealed the resident consciousness for landslide disasters, countermeasures and evacuation, which is a fundamental data for the policy of measures.
Regarding the organizations and systems, the Disaster Scheme mentions the responsibility and roles of 7 ministries and 11 organizations for emergency situations on natural disasters, especially that National Disaster Risk Reduction and Management Centre (hereinafter
1 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. NDRRMC) in Prime Minister Office undertakes a main role in disaster planning and coordination for every level on the central/local governments and establishes strategies for the disasters. RRU/LMU conducts monitoring, investigation, emergency response for landslides.
Under the landslide management plan 1 (survey and result) in Chapter 3, the identification of landslide hazard areas, topographic survey, geological survey, monitoring, geophysical exploration, drilling survey, field reconnaissance, disaster inspection, the review and recommendation for the Disaster Scheme as well as the Planning Policy Guidance (hereinafter PPG) and preparation of “Technical Guideline for initial survey” and “Procedure Manual for landslides” are described.
The targeted landslides in the Project are three (3) sites, Chitrakoot, Quatre Soeurs and Vallee Pitot by the hazard evaluation and the request form MPI. The following investigations and analyses have been conducted.
Table List of the Investigations and Analyses in the 3 Priority Areas (source: JET)
Chitrakoot Quatre Soeurs Vallee Pitot 1.8 km2 0.16 km2 0.005km2 Topographic plan map (1/500) (1800m×1000m) (400m×400m) (70m×70m) survey cross section (1/100) 3 lines 1 line 1 line Site reconnaissance 1 set 1 set 1 set physical test 6 samples 2 samples Laboratory test dynamics test 3 samples water quality 10 samples 7 samples rain gauge 1 1 extensometer 4 2 2 inclinometer 2 Monitoring strain gauge 2 2 ground water level meter 2 2 ground water level 6 (manual) elastic wave exploration 6 lines (1955m) Geophysical two-dimensional exploration 6 lines (1925m) resistivity exploration Drilling survey 6 holes (260m) 2 holes (42m) Survey on damage to houses 1 set 1 set 1 set
In addition to the above mentioned investigations and analyses, a disaster inspection has been implemented for the 37 hazard areas in the Disaster Scheme so that the areas have been classified into three (3) ranks (A, B, C) according to their level of risk. The issues and proposal on the early warning and evaluation protocol in the Disaster Scheme as well as the development control of landslides in the PPG have been discussed. “Technical Guideline for initial survey” and “Procedure Manual for landslides” have been published based on these investigations and analyses.
Under the landslide management plan 2 (analysis and interpretation) in Chapter 4, the geological interpretation, the interpretation for monitoring, the analysis for soil water index, stability analysis and susceptibility assessment are described.
The features and the policy of countermeasures have been discussed on the three (3) priority sites based on the results of the landslide management plan 1 in Chapter 3.
2 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. In Chitrakoot, although the entire block, which was presumably activated in 2005 and 2008, has already become stable, two small blocks, “A block (L=300m, W=150m)” and “B block (L=100m, W=200m)”, have been activated. The presumed slip surface is around GL-6m at the boundary between the base rock (Basalt) and the soft surface/colluvial soil. The landslide moves downward intermittently by rising of groundwater with rainfall so that the safety factor Fs is assumed to be 0.98. The rainfall is flooded on the surface due to poor drainage system, which would become a trigger by penetrating excessively into the ground of the landslide area. Therefore the establishment of surface and subsurface drainage systems is urgently needed.
In Quatre Soeurs, there seems to be an entire block by topographical interpretation, which is unclear and stable now. Although two small blocks, “A block (L=60m, W=50m)” and “B block (L=150m, W=100m)”, were presumably activated by 230mm accumulative rainfall in 2005 and 2008, they have been stabilized in the Project period. Since the landslides are stabilized, the safety factor Fs is assumed to be 1.00. The rainfall is flooded on the surface due to poor drainage system, which would become a trigger by penetrating excessively into the ground of the landslide area.
In Vallee Pitot, a small block, “A block (L=40m, W=40m)”, has been activated. The entire block (L=80m, W=100m) started to be activated in February 2013. It is presumed that the type is a surface landslide in colluvial soil/sand/clay. The landslide moves downward intermittently by rising of groundwater with rainfall so that the safety factor Fs is assumed to be 0.98. The rainfall is flooded on the surface due to poor drainage system, which would become a trigger by penetrating excessively into the ground of the landslide area.
In addition, thresholds of the early warning and evacuation using the Soil Water Index have been discussed by data in Mauritius Meteorological Service and of the Global Satellite Map of Precipitation (GSMaP) in Chitrakoot and Quatre Soeurs where there are history records on landslides.
For the Feasibility Study (hereinafter F/S) in priority areas in Chapter 5, the priority sites and pilot project sites, policy of countermeasures, Environmental Impact Assessment, the Pilot Project evaluation, the promotion of fund raising and the organizational reinforcement plan are described.
JET decided Chitrakoot as a Pilot site based on the landslide investigation, risk assessment, economic loss, countermeasure cost and request from MPI. For Chitrakoot, especially highest risk area “A block”, structural countermeasures such as drainage ditches by horizontal drilling were planned in order to avoid excessive water supply into the landslide area and to drain water safely away from the area. Environmental Impact Assessment has been conducted and their mitigation plan was reflected to the countermeasures. The pilot project evaluations (pre, interim, post) have been implemented from the viewpoints of relevance, effectiveness, efficiency, impact and sustainability.
In Quatre Soeurs, the Mauritius Government is negotiating with local residents in the landslide area to relocate them to a safer place and has had meetings with them more than ten (10) times since 2010. JET has supported MPI regarding the preparation of the explanation materials and the meetings. Although the Mauritius Government has proposed a place to relocate the residents, an agreement has not been reached with the residents, therefore the relocation has not yet been completed.
3 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. In Vallee Pitot, since a landslide block started to activate through February to May in 2013, the land mass destroyed a channel (20m) and has blocked it completely. JET proposed to C/P that emergency responses and permanent countermeasures after geological survey and monitoring and has discussed with MPI regarding this matter. MPI started the geological surveys and the monitoring there and is planning countermeasures.
Budget allocation after 2014 for the 37 hazard areas (including the three (3) priority sites) in the Disaster Scheme has been promoted by proposing the policy of investigation and countermeasures. MPI applied the budget for investigation/analysis/design/supervision for the 37 areas; 16,500,000Rs in 2014, 55,650,000Rs in 2015, 40,100,000Rs in 2016 and 44,700,000Rs in 2017.
Regarding the organizational reinforcement plan, JET proposed tasks to be conducted by organizing the current issues and purposes on RRU/LMU and has fulfilled, as mid/long term objectives, the request of six (6) full-time engineers, the budget application and the concretization of responsibility/role of related organizations, from standpoints of technological improvement, personnel securement and improvement of administrative ability. In addition, some of C/Ps have been dispatched to Japan to study at graduate university (two (2) years) and to train in disaster management (two (2) months).
For the Pilot Project in Chapter 6, the structural countermeasure in Chitrakoot, the early warning and evacuation system in the targeted three (3) sites, IEC (Information, Education and Communication) and stakeholder meetings are described.
As for the structural countermeasures in Chitrakoot, JET and C/P have implemented the basic design/detailed design/cost estimation/construction plan/bidding/contract/construction/ supervision for a large-scale channel, a horizontal drilling, an open/blind ditch, a surface ditch, a river improvement (widening and revetment work), a bridge and a collecting channel for the purposes of limiting the inflow of water into the landslide area and draining of water away from the landslide area. Since it takes time (around one (1) year) to get an official approval of land use for construction in Mauritius, JET and C/P prioritize the construction with consideration of safety and decided that JET would implement the higher prioritized works as a pilot project before the rainy season (December in 2014) and MPI would implement the remaining works after the rainy season with their own budget. The contract for the pilot project was awarded by competitive bidding in June 2014 at MPI office to a local construction company for 14,045,723Rs (lowest price). The construction was started on August 2014 and completed in December 2014 (around five (5) month). During the pilot project, the structure and alignment of the channel and vegetation works were locally modified and the river improvement at the bottom part (L=47m) was canceled because of a complaint from a landowner. The canceled works will be conducted by MPI after the rainy season. The monitoring such that using as groundwater level meters, extensometers and pipe strain gauges will be continuously conducted to identify the effectiveness of the countermeasures after the construction.
Regarding the early warning system, JET proposed new thresholds at which to issue warnings based on extensometer readings and house damage obtained in the monitoring of the Project. This proposal was the result of investigations looking into issues of the current system in the Disaster Scheme. The proposed threshold is; “preparation (pre stage)” is 20mm/month in extensometer or new cracks in houses, “warning (stage 1)” is 5mm/hour in extensometer or crack opening in houses, “evacuation (stage 2)” is 20mm/hour in extensometer or additional
4 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. cracks in/around houses, “warning lifted (stage 3)” is 0mm/hour in extensometer or no anomalies in houses. The revolving lights (red and yellow) and sirens have been installed to enable voluntary evacuation using the thresholds. The yellow light informs “warning (stage 1)” and the red light and siren inform “evacuation (stage 2)”. Liaison members and communication system as well as evacuation routes/areas for the early warning and evacuation have been established. MPI will continuously work to raise awareness of local residents under normal conditions, and check the areas and give advice to NDRRMC in emergency condition.
For IEC in the Project, JET has supported MPI to transmit the related information such as disaster, warning, evacuation and land use etc. through various media to residents. One of the main activities of IEC is stakeholder meetings for the residents in the three (3) priority areas, which were held five (5) times at the beginning of the Project, at the completion of implementation plan (draft), at the finalization of the implementation plan, at the beginning of the pilot project and at the end of the pilot project to get consensus and understanding from the residents. JET ascertained the level of understanding of the residents of the three (3) priority areas on how to respond to an early warning or evacuation order by questionnaire, and proposed measures and activities to be conducted by MPI. Newsletters in English/French (No.1-5) and “Landslide Disaster Prevention Handbook” were published and distributed to the local residents as well as the related organizations.
With respect to the technical transfer in Chapter 7, methodology and structure of the technical transfer, workshop, technical transfer seminar, training in Japan, Steering Committee and advisory committee in Japan are described.
In order to conduct effective technical transfers, the methodology and structure have been reconsidered based on the purposes and issues of OJT (On-the-Job Training), the Pilot Project, and the training in Japan. JET is composed of four (4) technical groups; a management group, an investigation/analysis group, a design/construction group and a soft countermeasure group for smooth technical transfer. MPI, as one entire team, has received technical training from all four (4) groups so that MPI has been able to understand whole knowledge and technology on the management and countermeasure on landslides.
In addition to the OJT, three (3) technical transfer seminars on the landslide countermeasures and 13 workshops on certain themes such as aerial photo interpretation and stability analysis etc. were held through the Project period. The trainings in Japan were held on November 20th – December 15th in 2012 and August 14th – September 8th in 2013 (both for 26 days) with participation of five (5) C/P members for each training (total ten (10) members). The Steering Committees in Mauritius and the Advisory Committee in Japan were held four (4) times for each committee to confirm the policy/methodology/results/discussion on the Project.
As for environment, climate change adaptation and disaster management in Chapter 8, the landslide management plan and the climate change adaptation plan have been discussed and proposed to the Government of Mauritius based on all of the activities in the Project.
As for the proposal for future tasks in Chapter 9, the tasks for each item on landslides in the Project have been summarized. Proposals on formulation of a landslide management plan in Mauritius are summarized as follows in consideration of the hypotheses for mechanisms and countermeasures on landslides.
1. The following basic surveys are necessary to grasp the landslide activities, volumes,
5 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. areas and the relation with circumferences. 2. The Disaster Scheme and the PPG are reviewed to propose the early warnings and evaluation protocols and other soft countermeasures. 3. The current activities on landslides are determined by the stability analysis using landslide cross sections based on the basic surveys. 4. The relations among the activities, groundwater level and rainfalls are discussed with the results of the monitoring. 5. Best countermeasures (hard and soft) are considered from the viewpoint of the activities, priorities, request form residents, and budgets. 6. For hard countermeasures, suitable drainage works are selected based on the results of the investigation on surface/ground water conditions. Horizontal drilling is judged to be effective from the results of the pilot project. 7. For soft countermeasures, early warning/evaluation system using a threshold for each landslide is operated. The soft countermeasures are useful until the completion of the construction of hard countermeasures.
6 Chapter 1
Introduction JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC.
1 Introduction
1.1 General This report is a Final Report (hereinafter F/R) which covers the results of all activities for the Project of Landslide Management in the Republic of Mauritius (hereinafter the Project) according to the Record of Discussion (hereinafter R/D) agreed upon between the Ministry of Public Infrastructure and Land Transport (hereinafter MPI), of the Republic of Mauritius (hereinafter Mauritius) and the Japan International Cooperation Agency.
JICA dispatches 14 experts (hereinafter JET, or JICA Expert Team) who specialize in investigation, analysis, design and countermeasure on landslide. The Project is conducted with members of the Repair and Rehabilitation Unit/ Landslide Management Unit (hereinafter RRU/LMU) in MPI as Counterparts (hereinafter the C/P) from May 2012 to March 2015.
1.2 Background of the Project Mauritius is vulnerable to climate change, particularly landslide issues are becoming more serious due to recent natural disasters resulting from environmental changes and the increase of structures because of tourism and land development on steep slopes. Mauritius has been taking disaster prevention measures as shown in Table 1.2.1. Although the country wishes to draw plans, understand risks and implement measures on scientific and technical grounds in consideration of environmental burden and safety management, it has not yet found a fundamental solution due to the lack of experts and engineers, and the lack of publicity of climate change adaption measures and disaster prevention administration to local communities.
Table 1.2.1 Overview of Landslide Damage and Countermeasures in Mauritius (source: JET)
Year Landslide Countermeasures 1986 A large scale landslide occurred in the La Butte area (1500 houses were damaged, 4 main water pipes and high voltage power lines were broken). 1989 JICA’s Port Louis City Landslide Countermeasure Planning Study began (1990). 1994 JICA’s Port Louis City Landslide Protection Project was approved (completed in 1998). 2005 A large scale landslide occurred in Chitrakoot (54 houses were damaged). A landslide occurred in Quatre Soeurs (11 houses were affected). 2006 A landslide reoccurred in Chitrakoot (14 houses were damaged) 2007 An elementary school in the landslide hazard area in Chitrakoot was closed. 2008 Landslides reoccurred in Chitrakoot and Quatre Soeurs (monitoring began). 2009 The Cyclone and Other Natural Disasters Scheme was established. Landslide Management Unit (LMU) was established in MPI.
Against such background, upon the request for technical assistance in landslide management from the government of Mauritius to the government of Japan, we have decided to carry out the Project for Technical Cooperation.
1-1 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. 1.3 Objectives of the Project
1.3.1 Objective
The goal is to have the Feasibility Study (hereinafter F/S) and landslide management plan approved by the Government of Mauritius, and for the relevant organizations to implement them.
1.3.2 Desired Outcome
The risk of landslides and other slope disasters is reduced, and the safety for the residents in the landslide area is secured.
1.3.3 Outcome of the Project
1) Formulation of a landslide management plan to establish a landslide monitoring system.
2) Implementation of the F/S and pilot project to examine, carry out and learn specific approaches.
3) Improvement of landslide management skills at RRU/LMU and other related Institutions.
1-2 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. 1.4 Scope of the Project
1.4.1 Project Areas
The project area is the Mauritius Island, and the JICA Expert Team prioritize 37 high risk areas designated in the Cyclone and Other Natural Disasters Scheme (hereinafter the Disasters Scheme).
Figure 1.4.1 Location Map of the Project Area (source: JET)
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1.4.2 List of JICA Expert Team and Counterparts
The C/P of the Project is MPI and, the C/P members are mainly composed of RRU/LTU in Civil Engineering Division in MPI.
The names of the JICA Expert Team (hereinafter JET) members and counterparts are listed below. Table 1.4.1 indicates the role of each member.
Table 1.4.1 List of JICA Expert Team and Counterparts (source: JET)
JICA Experts Field of Expertise Counterpart (MPI) 1 Kensuke ICHIKAWA Chief adviser Vice chief adviser/ Landslide 2 Takeshi KUWANO management 3 Tomoharu IWASAKI Landslide survey and analysis 4 Fumihiko YOKOO Landslide monitoring 5 Yoji KASAHARA Geophysical prospecting 6 Masami SUGITA GIS/Topographic survey Mahmad Reshad JEWON 7 Takashi HARA Design/Cost estimation Deevarajan CHINASAMY Water quality management/ 8 Takayoshi KURATA environmental and social Vishwahdass RAMDHAN consideration Selvanaden Pearia ANADACHEE Policy and planning of urban 9 Yoshizumi GONAI development and land use Mohammad Khalid MOSAHEB Institution/system 10 Shingo ICHIKAWA Rameswurdass RAMDHAN analysis/capacity development 1 Information, education and Lalitsingh BISSESSUR 11 Yurie KAWABATA communication Bhoopendra DABYCHARUN Coordinator/Landslide 12 Yosuke YAMAMOTO management assistant Coordinator/Institution/system 13 Haruka YOSHIDA analysis/capacity development 2 Coordinator/Policy and planning 14 Makoto TOKUDA of urban development and land use assistant
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1.5 Major Activities The following components have been conducted from the commencement of the Project in May 2012 up to now (Figure 1.5.1).
Component 1 “Basic survey” Component 2 “Formulation of a Landslide Management Plan”, Component 3 “Implementation of the Feasibility Study (F/S) in Priority Areas” Component 4 “Implementation of the Pilot Project”
For the basic survey (Chapter 2), the site reconnaissance results for the 37 landslide areas and their countermeasures, both structural and non-structural have been summarized based on the data collection and analysis. Social survey, survey related to institutions/systems and economic survey were implemented by mainly data collection and interview surveys. As a part of the social survey, the local resident consciousness on landslide management and countermeasures were summarized using questionnaire surveys for the local residents.
Under the landslide management plan (Chapter 3-4) a drilling survey and monitoring were conducted for the three target landslide areas selected by the basic survey. Stability analysis, susceptibility assessment and establishment of management plan for landslides have been conducted based on the drilling survey/monitoring analysis/geophysical exploration. The technical guideline for initial survey and the technical guideline have been established from the viewpoint of the site survey and the analysis. In addition, an entire landslide management plan, which includes a proposed early warning/evacuation system, a proposed Planning Policy Guidance (PPG) and the establishment of an improvement plan of organizations/institutes, has been prepared based on a review of existing guidelines, policies and systems.
The F/S in priority areas (Chapter 5) consisted of a plan/cost estimation/construction plan of countermeasures for the three target landslide areas, Pilot Project evaluation, budget allocation and proposal in MPI, an Environmental Impact Assessment and a sustainable organization system for landslide countermeasures have been implemented from both standpoints of “hard” countermeasures (structural countermeasures) and “soft” countermeasures (early warning system, etc.)
For the Pilot Project (Chapter 6), Chitrakoot has been selected as a target area, and the basic design, detailed design and cost estimation of the hard countermeasures have been conducted so that the drainage works and horizontal drilling works have been constructed in the area. During the construction, effort was made to ensure a sufficient exchange of information, education and communication (IEC) with respect to the related organizations and stakeholders (i.e. through meetings) to gain the understanding of the local residents. The early warning system by installation of monitoring devices has been established in the area, and the protocol for evacuation was proposed in the “Disaster Scheme”.
As for the technical transfer (Chapter 7), workshops on specific themes and a series of technical transfer seminars on landslide countermeasures are being conducted as well as the OJT (on-the-job training) in the Project. The Steering Committees and Advisory Committee in Japan to validate the procedure of the Project have been conducted with related organizations. Training in Japan has been successfully completed twice during the Project.
With respect to environment, climate change adaptation and disaster management (Chapter 8), the landslide management plan and the climate change adaptation plan have been discussed
1-5 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. and proposed to the Government of Mauritius based on tall of the activities in the Project.
1-6 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. Year 2012 2013 2014 2015 Contract Year First Year Second Year Japanese Fiscal Year FY2012 FY2013 FY2014 Calendar Month 56789101112123456789101112123456789101112123 Rainy season Rainy season Rainy season
1‐1 Collection, organization and analysis of existing materials and information 1‐2 Landslide inventory survey Component 1 1‐3 Survey on structural/non‐structural measures Basic Survey 1‐4 Social survey (questionnaires, etc.) 1‐5 Survey Related to organizations/systems 1‐6 Economic survey
2‐1 Identification of landslide hazard areas based on the landslide database 2‐2 Monitoringanalysis of landslide activities 2‐3 Stability analysis 2‐4 Susceptibility assessment 2‐5 Formulation of a landslide countermeasure plan 2‐6 Formulation of a monitoring plans Component 2 Formulation of a 2‐7 Review of the current warning/evacuation procedures, and recommendations Landslide 2‐8 Formulation of a technical guideline for the initial survey Management Plan 2‐9 Review of the Planning Policy Guidanced an Recommendations 2‐10 Formulation of a procedure manual including the technical guideline 2‐11 Formulation of an organizational reinforcement plan for RRU/LMU
2‐12 Formulation of a project implementation plan 2‐13 Stakeholder meetings 2‐14 Technology transfer Seminars
3‐1 Selection of priority areas
3‐2 Implementation of the F/S in priority areas Component 3 Implementation of 3‐3 Project evaluation (technical, economic and social aspects) the Feasibility Study (F/S) in 3‐4 Environmental impact assessment (EIA) Priority Areas 3‐5 Technology transfer seminars 3‐6 Promotion of fund raising
4‐1 Selection of project areas and design
Component 4 4‐2 Stakeholder meetings Implementation of the Pilot Project 4‐3 Implementation of the pilot project 4‐4 Feedback to the landslide management plan and F/S
Workshop
Seminar Seminar Component 5 Technology Transfer Training in Japan Training in Japan Technology exchanges with southwest Indian Ocean countries
IC/R writing Component 5 Report P/R writing Writing/Explanation/ DF/R explanation/discussion IT/R writing Discussion P/R explanation/discussion IT/R explanation/discussion DF/writing F/R submisson IC/Rexplanation/discussion Report ▲IC/R ▲P/R ▲IT/R ▲DF/R F/R▲
SC ▲SC ▲SC ▲SC ▲SC Figure 1.5.1 Flowchart of Project Activity (source: JET)
1-7 Chapter 2
Basic Survey JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC.
2 Basic Survey
2.1 Topography Figure 2.1.1 indicates the full view map of Mauritius. It is a volcanic island with craters distributed continuously from north to south of the island. A volcanic plateau of 300 - 400m is formed by these craters, with the highest peak being Mt. La Petite Riviere Noire (828m) in the southwest of the island. The outer rim of the craters is characterized by steep slopes while the coast side is generally flat. Also, faults of NNE-SSW and NW-SW directions are distributed along the outer rim of the craters, and are believed to be caused by volcanic activity.
Figure 2.1.1 Full View Map of Mauritius1
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2.2 Geology and Rainfall Figure 2.2.1 indicates the geological map of Mauritius. The island is a volcanic island and the basaltic flows are classified into 3 groups which are ancient lava series, intermediate lava series and recent lava series. The geological history began approximately 10 million years ago and there were two cycles of volcanic activity involved in the formation of the island. First cycle took part mostly at the south of the island, consisting basaltic and breccias of ancient lava series and formed a lava plateau. The second cycle took part mostly at the north of the island consisting basaltic and tuff from intermediate and recent lava series and deposited above the layer of ancient lava layer. Later, weathered colluvial and pyroclastic materials from the steep slope of mountain collapsed and deposited at the foot of the mountain, creating landslides within the tuff and colluvial deposits. Figure 2.2.2 indicates a cross section of a typical landslide (colluvial landslide): La Butte landslide.
Figure 2.2.1 Geological Map of Mauritius2
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Colluvium is supplied from mountains made of basalt, and, with pyroclastic materials, deposits at the foot of such mountains. Colluvium and pyroclastic materials are weak, and as a result landslides can be triggered by heavy rain and development activity - residential land development or road construction.
Mt Signal
Landslide area
Mt Signal
Earth removal work
Dense housing School Trace of reservoir Sea Road
Mosque
Estimated slip surface
Basalt Colluvium Pyroclastic material Clay of Pyroclastic material
Figure 2.2.2 Cross Section of the Typical Landslide (Colluvial Landslide): La Butte Landslide3 Figure 2.2.3 indicates the annual rainfall amount in Mauritius (1971~2000). The average annual rainfall amount is about 2000mm and almost 70% is concentrated during the rainy season (December ~ May). Many large-scale cyclones occur during the rainy season, causing most of the landslide disasters to occur during this season. Also, the annual rainfall amount at the mountain area in the center of the island is more than 4000mm, which, in addition to the expansion of development in the mountain area, is causing more landslide disasters.
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Isohyetal Map of Mauritius (1971-2000)
Long Term Average Rainfall Over Mauritius Period 1971 – 2000 Figure 2.2.3 Annual Rainfall Amount in Mauritius (1971~2000)4
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2.3 Landslide Inventory Survey To consolidate landslide information, the characteristics of landslides, evaluation results, and types and scale of countermeasures will be listed in a chart and compiled into a database. This database will allow us to promote the understanding of landslides and efficient disaster management in Mauritius.
In the landslide inventory survey, a reconnaissance will be conducted for the 32 landslide hazard areas selected in the "Cyclone and Other Natural Disasters Scheme 2011-2012" (Table 2.3.1). However, as a result of having investigated the sites, several of the 32 landslide hazard areas were divided, bringing the total to 37 areas. Table 2.3.2 lists the 37 landslide hazard areas after having reviewed the landslide hazard areas.
Table 2.3.1 32 Landslide Hazard Areas Selected in the Disasters Scheme5
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Table 2.3.2 Revised 37 Landslide Hazard Areas (source: JET)
No. Area name Pamplemousses/Riviere du Rempart District Council 1 Temple Road, Creve Coeur 2 Congomah Village Council (Ramlakhan) 3 Congomah Village Council (Leekraj) 4 Congomah Village Council (Frederick) 5 Congomah Village Council (Blackburn Lanes) 6 Les Mariannes Community Centre (Road area) 7 Les Mariannes Community Centre (Resident area) 8 L'Eau Bouillie Municipality of Port Louis 9 Chitrakoot, Vallee des Pretres 10 Vallee Pitot (near Eidgah) 11 LePouce Street 12 Justice Street (near Kalimata Mandir) 13 Mgr. Leen Street and nearby vicinity, La Butte 14 Pouce Stream 15 Old Moka Road, Camp Chapelon 16 Boulevard Victria, Montague Coupe Black River District Council 17 Pailles : (i) access road to Les Guibies and along motorway, near flyover bridge 18 Pailles : (ii) access road Morcellement des Aloes from Avenue M.Leal (on hillside) 19 Pailles : (iii) soreze regin 20 Plaine Champagne Road, opposite "Musee Touche Dubois" 21 Chamarel : (i) near Reataurant Le Chamarel 22 Chamarel : (ii) Roadside 23 Gremde Riviere Noire Village Hall 24 Baie du Cap : (i) Near St Francois d'Assise Church 25 Baie du Cap :(ii) Maconde Region GRAND PORT/SAVANNE DISTRICT COUNDIL 26 Riviere des Anguilles, near the bridge 27 Quatre Soeurs, Marie Jeanne, Jhummah Streert, Old Grand Port 28 Bambous Virieux, Rajiv Gandhi Street (near Bhavauy House), Impasse Bholoa 29 Cave in at Union Park, Rose Belle MUNICIPALITY OF CUREPIPE 30 Trou-AUX-Cerfs 31 River Bank at Cite L'Oiseau 32 Louis de Rochecouste (Riviere Seche) 33 Piper Morcellement Piat MUNICIPALITY OF QUATRE BORNES 34 Candos Hill at LallBahadoor Shastri and Mahatma Gandhi Avenues 35 Cavernous Area at Mgr Leen Avenue and Bassin MUNICIPALITY OF BEAU BASSIN/ROSE HILL 36 Morcellement Hermitage, Coromandel 37 Montee S, GRNW
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2.3.1 Classification of Hazard Area
The 37 landslide hazard areas, selected based on the "Cyclone and Other Natural Disasters Scheme 2011-2012", includes several disaster forms besides landslides (the object of this project). Therefore the 37 hazard areas are classified 9 kinds of disasters, given in Table 2.3.3, while Table 2.3.4 gives a description of the nine kinds of disasters.
General classification：At first, the 37 hazard areas selected based on the "Cyclone and Other Natural Disasters Scheme 2011-2012" are classified into two kinds of disaster, Slope disasters and Other disasters.
Sub classification：Then, Slope disasters are classified into Landslide, Slope failure, Rock fall, and Debris flow. Other disasters are classified into Stream erosion, Damage of embankment, Damage of wall, Damage of house, and Cavern.
Table 2.3.3 Classification of Hazard Area (source: JET)
General classification Sub classification Summary Can be classified as a Landslide 6 areas Landslide Hazard Area Slope 15 areas Slope failure 7 areas Rock fall 1 areas Debris flow 1 areas Because it is not a Disaster Stream erosion 10 areas "Landslide", it cannot be Damage of 4 areas classified as a Landslide Embankment Other 22 areas Hazard Area Damage of wall 5 areas Damage of house 1 areas Cavern 2 areas
Total 37 areas
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Table 2.3.4 Description of the Disaster Type (source: JET)
Slope disaster Other disaster A landslide is a phenomenon where the soil Stream erosion is the phenomenon where the mass on failure surfaces deep in the ground soil of the bank is removed by the flow of the gradually shifts downward, triggered by heavy river. It occurs in riverbanks where the flow of rain, an earthquake, river erosion or the river hits with the most force.Water might earthworks. Compared to slope failure, overflow when the level of the stream landslides are generally on a larger scale and increases. occur on gentler slopes (about 5-30 degrees). Stream Landslide erosion water colliding front Past riverbed Present riverbed
A slope failure is a mass becoming detached The collapse of the road embankment is from a steep slope/cliff along surface with little often triggered by rainfall, infiltration of or no shear displacement. Compared to underground water, erosion by surface water, landslides, the failure is rapid and on a or a partial catchment. It can be caused by small-scale, the inclination angle is a weak embankment material or by lack of soil relatively high (over 30 degrees). compaction. Concentration of Surface surface water Slope Damage of Rainfall failure embankment water
Surface water
Cross section Signs of stream
A rock fall is a phenomenon where foliated The disaster of a retaining wall doesn't occur rocks and gravel start to fall down a slope as a suddenly as with a rockfall etc., rather the result of enlarged cracks in the bedrock or deformation occurs over a comparatively long outcropped rocks. time. The survey should investigate: ・ condition around the retaining wall
Damage of ・ main body of the retaining wall Rock fall wall ・ history of the retaining wall
A debris flow is a phenomenon where soil A crack that occurs on the wall of a house and boulders are liquefied by surface water or may be caused by: groundwater and tend to flow downward ・ Lack of bearing capacity rapidly through a mountain torrent. ・ Subsidence of foundation ground ・ Shoddy workmanship, etc. Damage of Debris flow house
settling A cavern may be caused by: ・Infiltration of water from soak away ・Infiltration of water from improved pit, etc.
Soak away improved pit Cavern
Cavern
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2.3.2 Site Reconnaissance
The site reconnaissance will be conducted for 37 landslide hazard areas selected in the Disasters Scheme, and hazard evaluation will be conducted by checking disaster focus points. In addition, for landslides and slope failures, aerial photograph interpretation is carried out to confirm distribution of the landslide topography.
a. Aerial Photographic Interpretation
Most active landslides are characterized by certain landslide landforms. Aerial photograph interpretation is effective for observing landforms over a wide area and the chronology of those landforms, and then for considering the relations between those features and landslides.
A stereoscope can be used to view images in stereo using stereo-pair aerial photographs. From the stereo image, landforms caused by landslide movement and geomorphological features can be identified.
Photo 2.3.1 Aerial Photograph Interpretation (source: JET)
Some typical characteristics of landslides are:
・ Cross-section profiles show steep (main scarp) to gentle (middle part of landslide) and steep (toe part of landslide) from upper part to lower part. ・ Contour lines of topographic maps are not parallel but winding and irregular. ・ Main scarps, steps, cracks, depressions, ponds and swamps can be seen on the gentle slope. ・ Clear steam lines sometimes appear on side of the landslide.
The legends of aerial photograph interpretation are shown in Table 2.3.5. Table 2.3.6 indicates a list of aerial photographs obtained from Ministry of Housing and Lands (hereinafter MHL). The scale of aerial photograph is about 1:10,000.
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Table 2.3.5 Legends of Aerial Photograph Interpretation (source: JET)
A. Main and/or lateral scarp of which crown is fresh and dissected
B. Mostly dissected crown
C. Definite and probable margin of landslide mass with a main scarp at the backward or upper slope
D. Landslide body margin without main scarp and crown symbols
E. Crack with steps
F. Spring water
G. River system and bleeding channel
Table 2.3.6 List of Aerial Photographs (source: JET)
Index Number of No. Region Year Aerial photo No. photos 1998 R 717 - R 728 1 LES MARIANNES 1998 R 748 - R 752 1999 1926 - 1929 16 1998 R 741 - R 747 2 CREVE COEUR 1999 1920 - 1925 1991 53 - 55 16 1997 0501 - 0503 3 G.R.N.W - PORT LOUIS 1999 1911 - 1915 1999 1916 - 1919 12 1997 608 - 613 4 QUATRE - BORNES 1998 507 - 510 1999 1776 - 1782 18 1998 R 534 - R 538 5 CUREPIPE 1997 1340 - 1343 1997 1393 - 1396 13 6 UNION PARK 1999 1718 - 1719 2 1997 0139 - 0242 7 RIVIERE DES ANGUILLES 1997 1513 - 1515 1997 1527 - 1529 10 1991 180 - 182 8 LA MIVOIE 1991 199 - 200 5 1999 2072 - 2074 9 CHAMAREL 1998 R 650 - R 659 13 10 BAIE DU CAP 1998 R 297 - R 300 4 1991 R 243 - R 244 11 GRANDE RIVIERE SUD EST 1991 1568 - 1569 4 Total 113
The aerial photograph interpretation for landslides was carried out for 13 hazard areas, out of a total of 37, that were classified as a landslide or a slope failure. However, the aerial
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photograph interpretation was not carried out when the scale of the disaster was too small to make it out properly, or when the disaster has occurred more recently than the aerial photo.
The results of aerial photograph interpretation are summarized in Figure 2.3.1 below, with a sample photo-map and landslide distribution map of Chitrakoot area. Table 2.3.7 indicates the result of aerial photograph interpretation.
Figure 2.3.1 Example of the Result of Aerial Photograph interpretation - Chitrakoot area (Left: Photo Map, Right: Landslide Distribution Map) (source: JET)
Table 2.3.7 Summary of the Aerial Photograph Interpretation (source: JET)
Classifica- Interpreted Aerial photo No Area name Summary tion or Not No.(Year) Les Behind the slope failure at the roadside, a landslide body margin Mariannes Slope R720-R721 without main scarp has been confirmed. 6 Interpreted Community failure (1998) Centre 1922-1923 A clear main landslide was confirmed, and the definite margin of 9 Chitrakoot, Landslide Interpreted (1999) the several landslides were interpreted around it. Because a target area is small, the aerial photo cannot identify Not 1919-1920 10 Vallee Pitot Landslide it. Around a target area, the certain landslide landforms were not interpreted (1999) confirmed. The landslide of La Butte occurred in 1986, and the definite 1917-1918 13 La Butte Landslide Interpreted margin of a landslide was confirmed by aerial photograph (1999) interpretation. Old Moka 1916-1917 A landslide body margin without main scarp has been 15 Landslide Interpreted Road (1999) confirmed, and the landslide topography is not clear. Pailles: (i) Because a target area is small, the aerial photo cannot identify access road Slope Not 1913-1914 it. Around a target area, the certain landslide landforms were not 17 to Les failure interpreted (1999) confirmed. Guibies Because it is later than the photography year, as for the disaster Pailles : (iii) Slope Not 0502-0503 occurrence of the target area, the aerial photograph cannot 19 soreze regin failure interpreted (1997) confirm it. Around a target area, the certain landslide landforms were not confirmed. Plaine It was confirmed that the colluvium distributed around slope Slope R656,R657 20 Champagne Interpreted failure area. The cause of the slope failure is thought to be weak failure (1998) Road colluvium. Quatre R243,R244 The definite margin of several landslides was interpreted around 27 Landslide Interpreted Soeurs (1991) the disaster area. Bambous Slope Not 1568-1569 The target area could not be identified on the aerial photo 28 Virieux failure interpreted (1991) because it is too small. It could not be confirmed on the aerial photo because the slope Trou-AUX-Ce Slope Not 1395-1396 failure occurred after the photo was taken. No clearly 30 rfs failure interpreted (1997) distinguishable landslide landforms could be confirmed in the target area. Candos Hill at Not 1780-1781 The target area could not be identified on the aerial photo 34 Landslide Lall Bahadoor interpreted (1991) because it is too small. No clearly distinguishable landslide
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Shastri landforms could be confirmed in the target area. Morcellement The target area could not be identified on the aerial photo Slope Not 1914-1915 36 Hermitage, because it is too small. No clearly distinguishable landslide failure interpreted (1999) Coromande landforms could be confirmed in the target area.
b. Process of landslide hazard evaluation of site reconnaissance
In the site reconnaissance the disaster focus points were checked and the hazard of each was evaluated. Table 2.3.8 indicates the disaster focus points for landslide hazard evaluation.
Most active landslides are characterized by certain landslide landforms. The site reconnaissance is carried out to check the landslide micro landforms. Another purpose is to find out what kind of landslide countermeasures have been undertaken and damage to houses that has occurred.
Table 2.3.8 The Disaster Focus Points for Landslide Hazard Evaluation (source: JET)
Category Check points Scarp (Main or Minor, Horse shoe shape) Transverse Cracks (Tension or Compression) Pond, Swamp Spring Water Phenomenon on the Topography of Steps Site Embankment at upper part Cut Slope at the toe Wash out by river Damage to buildings, houses Monitoring Equipment Existing record of Landslide History (documents or oral communication) No Existing Countermeasures Countermeasure Effectiveness of Countermeasure
Figure 2.3.2 Schematic Diagram of Landslide Landforms (source: JET)
c. Result of Site Reconnaissance
The results of the site reconnaissance are recorded in a landslide recording sheet, including
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the disaster focus point, its location, scale, on-site photographs, and description of the site.
Landslide recording sheet consists of general information sheet, evaluation sheet, and photograph sheet. The contents of each sheet are as follows;
General information sheet: In the general information sheet the address, position coordinate, schematic sketch, and location map (Scale: 1:25,000) are recorded. Evaluation sheet: In the evaluation sheet the disaster focus points and a description of a site are recorded. Photo sheet: In the photo sheet photographs such as the damage situation and the landslide landforms are recorded.
The landslide recording sheet of 37 areas is attached at the end of the report, and Figure 2.3.3 - Figure 2.3.5 are examples of the landslide recording sheet.
In addition, Table 2.3.9 indicates an item and the score of the landslide hazard evaluation by the site reconnaissance. The landslide hazard evaluation by site reconnaissance found three areas with high scores (6 points in total), Chitrakoot area, Vallee Pitot area, and Quatre Soeurs area (Table 2.3.10).
Table 2.3.9 Description of Scoring Sheet for Evaluating Landslide Hazard (source: JET)
Category Score Description Obvious 2 Definite landslide Landslide landforms and Slight 1 Undefined landslide, or slope failure characteristics None 0 Not a landslide Obvious 2 Heavy damage, situation is urgent Damage to buildings, Slight 1 Light damage, not urgent on the Site houses Phenomenon None 0 No damage Existing record of Obvious 2 Definite document and oral record exists Landslide Slight 1 Undefined document and oral record exists
History (documents or oral record) None 0 No existing record
Table 2.3.10 Result of Landslide Hazard Evaluation (source: JET)
Kind of the disaster Score of landslide hazard evaluation Landslide Damage to Existing No. Area name General Sub landforms buildings, record of Total classification classification and houses landslides characteristic Chitrakoot, Vallee 9 Slope Landslide 2 2 2 6 des Pretres Vallee Pitot (near 10 Slope Landslide 2 2 2 6 Eidgah) Mgr. Leen Street 13 and nearby vicinity, Slope Landslide 2 1 2 5 La Butte Old Moka Road, 15 Slope Landslide 2 1 0 3 Camp Chapelon 27 Quatre Soeurs, Slope Landslide 2 2 2 6 34 Candos Hill Slope Landslide 2 1 0 3
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Figure 2.3.3 Example of the Landslide Recording Sheet, Chitrakoot Area (source: JET)
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Figure 2.3.4 Example of the Landslide Recording Sheet, Vallee Pitot Area (source: JET)
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Figure 2.3.5 Example of the Landslide Recording Sheet, Quatre Soeurs (source: JET)
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2.3.3 Inventory and Location Map
As a result of site reconnaissance, the characteristics and evaluation of the landslides were compiled and made into a landslide inventory (Table 2.3.11) and a landslide location map (Figure 2.3.6).
Figure 2.3.6 Landslide Location Map (source: JET)
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Table 2.3.11 Landslide Inventory (source: JET)
(1):Landslide landforms and characteristic, (2):Damage on construction and houses, (3):Existing record of Landslide Score of landslide Kind of the disaster Summary of the field investigation and hazard evaluation no. Area name interview General Sub (1) (2) (3) Total classification classification Deformation on the concrete block wall and house caused by embankment deformation at the front yard (parking Temple Road, Creve Damage of － －－－ 1 Coeur area) was confirmed. Another problem Other wall was inadequate surface drainage causing surface water from mountains to flow directly at houses during heavy rain. A small stream flows under the road Congomah Village through a concrete pipe culvert, Stream 2 however, because it is too small it Other － －－－ Council (Ramlakhan) causes flooding and bank erosion during erosion heavy rain. A 1m high retaining wall that was Congomah Village constructed to build the road was Damage of 3 reported to be leaning but it was found to Other － －－－ Council (Leekraj) be stable and no slope failure was wall observed. The 1m high retaining wall along the 4 Congomah Village road was found to have collapsed due to Other Damage of － －－－ Council (Frederick) erosion by surface water flow during wall rainy season. Congomah Village 5 Council (Blackburn A slope failure was confirmed on the side Other Damage of － －－－ of the road. Embankment Lanes) There are a few slope failures and a lanslide in this site. The slope at the Les Mariannes roadside collapsed during heavy rain in 6 Community Centre (Road 2010 and a section of road was washed Slope Slope － －－－ failure area) away. Since then, a retaining wall has been constructed and the site is currently stable. Les Mariannes 7 Community Centre There appeared to be bank erosion on Other Stream － －－－ the left bank above the bridge. erosion (Resident area) The cracks have been spotted on the 8 L'Eau Bouillie road surface due to the deterioration of Other Damage of － －－－ bearing capacity of the roadbed. Embankment However, the cracks have been repaired. A clear landslide was confirmed. A landslide was reported to have damaged houses and a school after heavy rain in 2005. Drilling investigation and Chitrakoot, Vallee des monitoring have been carried out, but not 9 Slope Landslide Pretres sufficiently. No countermeasures have 2 2 2 6 been implemented. Therefore, a detailed investigation and monitoring are necessary while the countermeasures are expected in future. Lately, housing developments are growing rapidly in this area. A landslide boundary of 35m x 20m was clearly 10 Vallee Pitot (near Eidgah) detected. Several houses have been Slope Landslide 2 2 2 6 damaged and some cracks were observed. The situation of the damage was also reported in the newspaper. Insufficient surface drainage means rain water concentrates in low area and erodes roads and houses in its path. Stream － －－－ 11 LePouce Street Damage is negligible at present, Other erosion although the maintenance of the surface drainage will be necessary. An embankment has been constructed to build up the road, which caused an adjacent retaining wall to be pushed out Justice Street (near Damage of － －－－ 12 Kalimata Mandir) and deformed. Insufficient surface Other wall drainage causing accumulation of groundwater could also be a factor causing this deformation. The landslide of La Butte occurred in 1986, and many houses and a school were damaged. As for this landslide, Mgr. Leen Street and countermeasures were carried out in 13 Slope Landslide nearby vicinity, La Butte 1998, therefore further investigation of 2 1 2 5 the landslide is unnecessary. However, Port Louis City wants to continue the monitoring on this landslide in the future.
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Every side of the channel is covered by concrete. The water level rises until the upper edge of the channel and erode beyond this point in the rainy season. The gabion has been set up at the lower 14 Pouce Stream part of slope at the channel and no Other Stream － －－－ damage has been reported yet. erosion However, the deteriotion of the concrete wall is remarkable and the extention of the wall height will be necessary. Therefore, further investigation and countermeasures are advisable. The landslide topography is not clear, but five houses and two retaining walls were damaged while the spring water was spotted in two places. There are two 15 Old Moka Road, Camp possible causes of this, creep Slope Landslide Chapelon transformation of weak surface soil or a 2 1 0 3 shallow landslide. Therefore, landslide investigation and monitoring are necessary while the countermeasures are expected in future. The gabion was installed on the cut-slope when the road was 16 Boulevard Victria, constructed. There is no record of Other Damage of － －－－ Montague Coupe damage for this site but the angle of the wall wall is steep.Therefore, the observation of this wall is advisable. The slope failure has been spotted along Pailles : (i) access road to Les Guibies and along the cut-slope (5m height) at the roadside Slope 17 of highway. The surface of the cut-slope Slope － －－－ motorway, near flyover has been weathered, and it is eroded by failure bridge rain. Pailles : (ii) access road Insufficient drainage is causing erosion 18 Morcellement des Aloes at the base of the water tank. Immediate Other Stream － －－－ from Avenue M.Leal (on erosion hillside) remedial work is needed. Falling rocks at the upper slope and shallow slope failure at the middle and 19 Pailles : (iii) soreze regin lower slope occurred in an area of Slope Slope － －－－ housing. There is only slight damage for failure now, although shallow slope failure and cracks have been confirmed. Retaining walls have been constructed as countermeasures where the slope Plaine Champagne Road, failure has been confirmed. It is currently 20 opposite "Musee Touche stable, although there were a few cracks Slope Slope － －－－ failure Dubois" spotted in the retaining walls which are believed to be due to substandard construction. Cracks in the road shoulder have Chamarel : (i) near occurred due to a lack of bearing Damage of 21 Other － －－－ Reataurant Le Chamarel capacity . It is caused by insufficient soil Embankment compaction. Deformation of the road has been confirmed at the shoulder of the road due to a lack of bearing capacity. The Damage of 22 Chamarel : (ii) Roadside Other － －－－ embankment of stone masonry wall and Embankment retaining wall were constructed but it is insufficient. The crack at the base of village hall area and edge of concrete basketball court has been confirmed. However, the surrounding structures are not affected, 23 Gremde Riviere Noire therefore it is considered unlikely this Other Damage of － －－－ Village Hall house damaged was caused by landslides. Rather it is likely to be caused by lack of bearing capacity of the ground or a problem with the structure itself. A debris flow has occurred in the past Baie du Cap : (i) Near St and a block wall has since been 24 constructed. Also, small surface failures Slope Debris flow － －－－ Francois d'Assise Church have been observed frequently in this area. A new road was built to reduce the damage from rock falls. However, rock Baie du Cap :(ii) falls and small rock failures are also a － －－－ 25 Maconde Region frequent occurance along the new road. Slope Rock fall The rocks are weathered, and there is a high possibility of rock fall in future. There are many houses built on the cliff here. The cliff is weathered severly and 26 Riviere des Anguilles, stream erosion occurs frequently. Other Stream － －－－ near the bridge erosion Therefore, the house will need to be relocated.
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Landslide activity has been confirmed at the Quatre Soeurs area where many houses have been damaged. The groundwater level at the lower part of the Quatre Soeurs, Marie landslide is high and is causing instability 27 Jeanne, Jhummah Slope Landslide 2 2 2 6 Streert, Old Grand Port in the landslide. Drilling investigation and monitoring have been carried out, but not sufficiently. Further investigation and monitoring are necessary while the countermeasures are expected in future. Slope failure was confirmed at the Bambous Virieux, Rajiv backyard of the house. No damge on the Gandhi Street (near house was reported although the soil of Slope 28 Slope － －－－ Bhavauy House), the slope approached near the house. A failure Impasse Bholoa retaining wall has been constructed independently. A cavity (4m x 4m x 3m depth) due to land subsidence was observed in the 29 Cave in at Union Park, residential area. No damage was caused Other cavern － －－－ Rose Belle to the houses and the cavity was filled in with soil. Similar situation was confirmed nearby. The slope failure in the crater of the volcano occurred during heavy rainfall in Slope 30 Trou-AUX-Cerfs 2005. The possibility of slope failure on Slope － －－－ the rear side is low. However, the slope failure failure on both sides can be expected. Bank erosion and flooding is common in the rainy season when the river water level rises. There are more damage on 31 River Bank at Cite the left side of the riverbank due to the Other Stream － －－－ L'Oiseau erosion strong collision of water. However, past damage has been restored by constructing a retaining wall. The bank erosion and flood are common Louis de Rochecouste in the rainy season. The base of the Stream 32 Other － －－－ (Riviere Seche) houses have been eroded and the erosion retaining wall of the houses are inclined. The bank erosion and flood are remarkable in the rainy season. 33 Piper Morcellement Piat However, the past damage has been Other Stream － －－－ erosion restored by constructing the retaining wall. A clear landslide site was confirmed at the backyard of the house. The landslide Candos Hill at topography and slope are clear while the 34 LallBahadoor Shastri and spring water has been observed. The Slope Landslide Mahatma Gandhi scale of this lanslide is small (40m x 2 1 0 3 Avenues 35m) and no house on the lanslide area. Only slight crack has been confirmed on the retaining wall. A cavity was reported during the house Cavernous Area at Mgr construction but it was filled with － －－－ 35 Leen Avenue and Bassin concrete. There is no further danger at Other cavern this site. At this slope, slope failure occurred in 2010, and a road was destroyed. After a retaining wall was made as a countermeasure, large-scale slope 36 Morcellement Hermitage, failures have not been found. However, Slope Slope － －－－ Coromandel the stone blocks from on top of the failure retaining wall have fallen down. This is likely caused by the ground behind the retaining wall sinking due to lack of compaction of the backfilling soil. Weathered outcrops were detected on 37 Montee S, GRNW both sides of the bank. The erosion is Other Stream － －－－ erosion remarkable in the rainy season.
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2.3.4 GIS Database
As a result of landslide survey, it turned out that long-term maintenance and control of spatial information of topography and geographical features and all kinds of information obtained by works such as survey, plan and design are requested in a series of operations like countermeasure plan and construction.
So GIS (Geographic Information System) is thought to be the best system for maintenance and control of these information.
In this project, GIS database is created by using ArcGIS because it is in heavy usage in related other project (ex. Development of a DDR Strategic Framework and action Plan) and in Mauritius and ArcGIS software is compatible with other GIS softwares such as MapInfo, AutoCAD, Quantum GIS, etc.
In addition, on coordinate system of map information, it was decided that following system was used.
Coordinate System： Projection Universal Transverse Mercator
UTM40S zone
Geographic Coordinate System GCS_WGS_1984
Next, Use of GIS data created by field survey, existing GIS data and Excel data/reports to create a new GIS data is shown in Figure 2.3.7.
Existing (same) New GIS data from field Excel/Book, GIS Data survey Reports
Analysis/Edit
Use existing GIS data to create a GIS database of the target
Figure 2.3.7 Flow to Create A Database Using the ArcGIS (source: JET)
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a. Graphic Information
Graphic information can be classified into following two types.
Table 2.3.12 Existing GIS Data Collected in Mauritius (source: JET)
No Thematic Map Data style Data type Source Topographic Map(1:25,000)、Aerial MoESD 1 Raster Tiff/Jpeg photo、Satellite Image(:0.15Pixcel) MHL 2 Roads, River, contour line Vector Line MoESD Geology, National Boundary, 3 Vector Polygon MoESD Province Boundary
Table 2.3.13 New GIS Data Obtained from Field Surveys, etc. (source: JET)
No Thematic Map Data style Data type Source 1 Landslide Location Map Vector Point The data were made by 3 Landslide distribution Map Vector Polygon this project
b. Attribute Data
Attribute information is written in the DBF file form of characters, numeric and quantities as information related to graphic information. In a single administrative field attribute information such as the name and population has been entered, for example. And in geological map, geology name, geology code, large classification name, code and small classification name, code are entered as attribute information. Other than these, a number of individual information is added as attribute information. By using these attribute information, data search function or graphic display function or change of display color, thickness, and size are available.
Next, links of graphic information and attribute information by using political boundary data are explained in Figure 2.3.8. On the right side of Figure, political boundary map consists of small administrative boundaries is shown. Many small areas can be seen in map information and area information (Name, Latitude, Longitude, and Area) is entered in each area as attribute data. This attribute data is shown on the left side of Figure. It is possible to control map information from an item in attribute data and also to search for attributes data and political boundary map data to each other. In this sample, if click on No3 in the attribute data, color of one area of political boundary map changes. This is an example of search and display of No3 position in the map.
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Figure 2.3.8 Sample of Link of Political Boundary Map and Attribute Data (source: JET)
c. Various Functions
Using a database, it is possible to create and view the inventory recording sheet and landslides recording sheet by utilizing functions of GIS software. Other functions of GIS software are as follows; ・View of landslide recording sheet ・View of landslide location ・Landslide distribution map ・Landslide distribution map at pilot site ・Landslide locations in the range of the number of specific ・The area of the landslide block in specific range ・GIS data converting to CAD files ・Editing tasks, such as revision and update of the database
d. Creation of a New Thematic Map
By combining following three information (field survey information, existing information and new created information), new thematic mapping is possible. Landslide location diagram and landslide distribution map are included under this new thematic map. The following is an example of new thematic map that can be utilized to manage landslide survey from information had been obtained so far.
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Figure 2.3.9 Landslide Survey location Map Figure 2.3.10 Landslide Survey location Map (Base Map: Topographic (Base Map: Roads, River, contour line, Map(1:25,000))(source: JET) Province Boundary)(source: JET)
Figure 2.3.11 Landslide Distribution Map, Figure 2.3.12 Landslide Distribution Map, Chitrakoot Area (source: JET) Quatre Soeurs Area (source: JET)
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2.4 Existing Countermeasures Information will be collected for structural and non-structural measures required for landslide management planning as described below.
Table 2.4.1 Survey on Structural/Non-structural Measures (source: JET)
Item Survey Method Existing landslide Study of design documents and interviews with related parties on past countermeasures countermeasures, their locations, effects and problems Landslide monitoring, Interviews with related parties on the types, numbers and specifications of warning threshold, existing monitoring devices, measurement methods, systems and methods communication of analysis. In addition, threshold for giving and transmitting warning and means, evacuation evacuation support systems will be clarified. support Past damage, and residents’ recognition of warnings, of landslide precursors, and of hazard and evacuation areas were surveyed to Residents’ awareness understand their awareness of slope disasters. Detailed information on the and relocation relocation of residents such as background information and problems will also be collected. Documents/drawings on land/structure use, landslide legislation, Land use restrictions development regulations, upper level/related plans will be collected and in hazard areas interviews with relevant institutions will be held as necessary.
2.4.1 Structural Countermeasures
The Survey of structural countermeasures was carried out by studying design documents and interviewing related parties on past countermeasures, their locations, effects and problems.
The only landslide for which structural countermeasures have been carried out is that in La Butte area (Table2.4.2). The landslide of La Butte occurred in 1986, and many houses and a school were damaged. Countermeasures were undertaken in 1998 by help of Japan (Figure 2.4.1), and it has been stable since. However, Port Louis City wants to continue the monitoring on this landslide in the future.
Table 2.4.2 The Structural Countermeasures of Landslide Hazard Area (6 Areas) (source: JET)
Manage Kind of the Area name Structural countermeasures -ment no. disaster 9 Chitrakoot, Vallee des Pretres Landslide Non 10 Vallee Pitot (near Eidgah) Landslide Non Pile works: 6 lines Mgr. Leen Street and nearby vicinity, 13 Landslide Drainage wells: 4 wells La Butte horizontal drain works: 42 pipes 15 Old Moka Road, Camp Chapelon Landslide Non Quatre Soeurs, Marie Jeanne, 27 Landslide Non Jhummah Streert, Old Grand Port Candos Hill at LallBahadoor Shastri 34 Landslide Non and Mahatma Gandhi Avenues
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CONSTRUCTION SITE FOR LONG TERM PROTECTION MEASURS
Drainage well Horizontal drain Work
Document GOVERNMENT OF MAURITIUS LANDSLIDE COUNTERMEASURES PLAN AND INVESTIGATION IN PORT LOUIS, FINAL REPORT, ABSTRACT: JICA, 1990 Project GOVERNMENT OF MAURITIUS LANDSLIDE PROTECTION PROJECT IN PORT LOUIS: JICA Number of structural Pile works: 6 lines, Drainage wells: 4 wells, horizontal drain works: 42 pipes measures Figure 2.4.1 The Landslide Structural Countermeasures in La Butte Area6
2.4.2 Non-Structural Countermeasures
Existing non-structural countermeasures such as landslide monitoring equipment, warning standards, information communication methods, evacuation support, awareness of residents and land use restrictions were investigated as part of a survey of landslide hazard areas,
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which are listed in the Cyclone and Other Natural Disasters Scheme.
Landslide monitoring equipment was confirmed in Chitrakoot, Quatre Soeurs and La Butte. The following table shows the contents of monitoring equipment and their condition.
Table 2.4.3 Current Condition of Landslide Monitoring in Mauritius (source: JET)
District Contents of Landslide Monitoring Chitrakoot Three extensometers were confirmed to exist. Two of them are working. The data is measured by a Mauritian construction company. Quatre Six boreholes for groundwater monitoring were confirmed to exist. These were installed Soeurs in March 2011, and were used for monitoring until May 2011. It is able to use those boreholes, but the monitoring has not been implemented.7 La Butte Sixteen extensometers were installed and had been used for monitoring, but the monitoring and maintenance have not been implemented from 2011. Two of sixteen extensometers, three of seven tiltmeters and two of ten groundwater piezometers are functional.8
The survey for making landslide inventory by this project could not confirm any original warning standards, communication methods or evacuation assistance in the landslide hazard areas selected by the Cyclone and Other Natural Disasters Scheme.
Details of warning systems, communication methods and evacuation assistance at the national level are covered in the section of The Landslide Emergency Scheme in the Cyclone and Other Natural Disasters Scheme. These are reported in this report’s Chapter 5.3 Early Warning and Evacuation. And awareness of residents and land use restrictions of high-risk areas are also reported in chapters 2.5 Social Survey and 3.10 Review and recommendation for the Planning Policy Guidance.
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2.5 Social Survey
2.5.1 Basic Information Survey
This survey was implemented to collect the basic information for the review of the PPG, IEC (Information Education Communication) activities (such as enhancement of awareness of the disaster mitigation and evacuation drill/exercises), the feasibility study and the pilot project. The data collection results are shown as below.
a. Land Use
Figure 2.5.1 shows the land use map of Mauritius. Table 2.5.1 shows land use changes per category in Mauritius during the period 1986 to 2010.
Figure 2.5.1 Land Use Map9
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Over the last 25 years (1986 to 2010), changes within each land use category have ranged from slight to extensive. About 14% of agricultural land (excluding abandoned sugar cane land), and 5% of forest, shrub, range and grazing land, have been lost. On the other hand, built-up areas have increased by 12% and road infrastructure by 127%. However, the horizontal sprawl of built-up areas has been less obvious, due to the tendency to build vertically as compared to the horizontal expansion of the road network. Enlarging and upgrading of existing roads such as the conversion of highway to dual carriageway and the addition of new roads have also been important during this period of 1986 to 2010.
Expansion has been at the expense of agriculture. Loss of agricultural lands concerned mainly sugar cane lands, which were for instance released for property development and other housing projects. In addition, some agricultural land had been acquired for road development projects.
Table 2.5.1 Land Use Changes as Per Category in Mauritius During the Period 1986 to 20109
Area (ha) Change Land use category 1986 2010 Difference [%] Agriculture (sugar cane and other) 90,000 77,418 -12,582 -14 Abandoned sugar cane lands n/a 1,468 1,468 n/a Forest, shrub, and grazing land 65,400 68,946 3,546 5 Built-up area 25,000 28,070 3,070 12 Infrastructure (roads, footpaths) 3,465 7,879 4,414 127 Inland water resource system 2,610 2,719 109 4 Total 186,475 186,500
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b. Distribution of the Population
Figure 2.5.2 shows the population distribution map. In Mauritius, all the towns starting from the capital city of Port Louis to the town of Curepipe, are situated along a corridor/main motorway. All these urban areas have many services and amenities ranging from government offices to libraries. As can be seen from the map, the rest of the settlements consist of villages. Some are big with a population of 10,000 to 30,000. These big rural areas are fast developing into dynamic economic centres, e.g. Flacq, Mahébourg and Goodlands.
57°30'0"E 540000 550000 560000 570000 580000
Roads Motorway ´
7800000 Population 7800000 - 3000 3000 - 6000 6000 - 12000 12000 - 24000 24000 -
Pereybère Pointe aux 7790000 Roches 7790000 Mon Grand 20°0'0"S Choisy Grand Gaube 20°0'0"S Baie Goodlands
Triolet 7780000 7780000 Rivière du Roches Pamplemousses Rempart Noires
PORT LOUIS Poste de Pointe aux Bon Flacq Sables Accueil 7770000 Centre 7770000 de Flacq
Beau Moka Trou Bassin Rose d'Eau Hill Douce Quatre Belair Flic en 7760000 Flac Bornes 7760000 Phoenix Vacoas
Floreal Curepipe Petit Tamarin Sable Baie de la Grande Vieux 7750000 Riviere Noire Grand 7750000 Port
Ville Rose Noire Grand Belle Mahebourg Bois 7740000 7740000
Chemin Grenier Savannah 20°30'0"S Souillac 20°30'0"S 7730000 7730000
05102.5 km
540000 550000 560000 570000 580000 57°30'0"E
Figure 2.5.2 Population Distribution Map10
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c. Distribution of Poverty
Figure 2.5.3 shows the poverty distribution map by the Central Statistical Office of Mauritius. A poverty distribution map is a spatial representation of poverty indicators at disaggregated geographical regions. It gives an overview of the disparities that exist in poverty level within a country. The maps depict the poverty rate in each of the administrative regions.
Proportion of poor persons [%] ■15-35 ■10-15 ■5-10 ■0-5
Survey result of 2001-2002 Survey result of 2006 - 2007 Figure 2.5.3 Poverty Distribution Map11
A comparative analysis of the poverty rates for 2001/02 and 2006/07 indicates that:
・ Among the 5 Municipal Wards with the lowest poverty rates in 2001/02, 4 remained in the same position in 2006/07. These are Wards 1 & 2 of Quatre Bornes, Ward 4 of Beau Bassin / Rose Hill and Ward 3 of Vacoas-Phoenix. However, Ward 1 of Vacoas-Phoenix which ranked 4th in 2001/02 (poverty rate of 2.6%) dropped to rank 18 in 2006/07 (poverty rate of 4.7%). ・ There were 48 Municipal Village Council Areas where poverty was not highly prevalent (with a rate below 5%) in 2001/02. In 2006/07 the number decreased to 20. In 2001/02 there were 4 Municipal Village Council Areas with high poverty rate (above 15%). In 2006/07, the number increased to 15. ・ Out of the 145 Municipal Village Council Areas, 26 areas, located mostly in the district of Rivière du Rempart, witnessed major improvements in their poverty rank (rank difference of 20 or more between 2001/02 & 2006/07). On the other hand, 24 Municipal Village Council Areas located mostly in the eastern and southern part, witnessed a major deterioration in their poverty rank.
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d. Water Resources
Figure 2.5.4 shows the distribution map of principal water resources in Mauritius. In Mauritius, water is obtained from springs, reservoirs, rivers and boreholes. There is an increasing demand for water for domestic, agricultural and industrial uses. It is obtained of domestic water supply from reservoirs built on the Central Plateau. As can be seen from the map, boreholes situated mostly on the western part of the Central Plateau and the Northern Plains provide us with domestic water supply. Some rivers have been dammed to provide water for domestic use. The reservoirs of La Ferme and La Nicoliere and part of the Midlands Dam are used for irrigating agricultural land.
Figure 2.5.4 Distribution Map of Principal Water Resources in Mauritius12
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The whole population of Mauritius has access to piped potable water. The Housing and Population Census 2000 survey reveals that 98.7% of the population had access to piped potable water within their premises, with 85.5% having piped water inside their house as compared to 75% in 1990. The remaining 1.3% of the population relied on public fountains, CWA (Central Water Authority) mobile tanker service and other sources for their daily supply of potable water. The CWA estimates that the average demands for potable water from households is 170 L/h/d and non-domestic demand is equivalent to 441 L/h/d. Water is used for different purposes as shown in Table 2.5.2.
Table 2.5.2 Water Utilization13
Surface Water Purpose Groundwater Total River-run Off-takes Storage Domestic, Industrial and 38 48 113 199 Tourism Industrial (private boreholes) -- 10 10 Agricultural 370 76 22 468 Hydropower 131 174 - 305 Overall Utilization 539 298 145 982 (Unit: million cubic meter per year)
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2.5.2 Attitude Survey about Landslide Disasters The attitude survey was implemented to collect the basic information for the review of the PPG and IEC (Information Education Communication) activities (such as enhancement of awareness of the disaster mitigation and evacuation drill/exercises). The following table shows the summary of the survey.
Table 2.5.3 Summary of Attitude Survey about Landslide Disasters (source:JET)
Item Content Period From beginning of August to middle of September Respondent / Number of Whole of Mauritius: about 300 households responses Schedule
< About the setting the respondents >
A representative sample of respondents was selected impartially from the nine local authorities.
Social workers who know the existing situation of their own region and are aware of the local residents were recommended as respondents by MPI, MHL, MLG and Local Authorities. Social workers are not affected by politics, religion and ethnic group, and can tell residents’ opinions to the Local Authorities. Based on the above, the survey tried to find social workers as respondents, but when it was difficult to find them, a randomly selected resident was set as a respondent.
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The following table shows the items and content of the survey sheet.
Table 2.5.4 Items and Content of the Survey Sheet (source: JET)
Item Content Age, Sex, Length of residence, Land ownership of the Basic Information residence, House ownership Awareness about landslide Recognition about landslide, Experience of landslide damage, disaster and experience Worry of landslide damage Recognition about the early Recognition of the warning system of Mauritius, Needs of the warning system warning system, Necessary information for warning system Recognition about the Recognition of the existing development/building restrictions, development/building Recognition of development restriction in slope area. restrictions Establishment of the Establishment of the landslide caution zone, Need of landslide caution zone explanation about the landslide caution zone by government. Hazard map Needs of publicity of the hazard map Needs of development/building restriction, Needs of advice for Restriction in the landslide building by Local Authority, Needs of relocation, Assistance for caution zone relocation by government, Motivation for relocation Evacuation action in landslide occurrence, Participation experience of evacuation drill/exercise, Intentions to join Evacuation exercise evacuation drill/exercise, Motivation for participation in evacuation drill/exercise Free comment Free comment for landslide disaster
The following simple tabulation results are reported in this report because of space constraints. The detailed result of each question is shown in the Supporting Report.
(a) Summary of simple tabulation results of all respondents (b) Comparison of simple tabulation results of the 3 pilot sites (Chitrakoot, Quatre Soeurs, Vallée Pitot)
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a. Summary of Simple Tabulation Results of All Respondents
Main points obtained by the simple tabulation are shown in the following table as a summary of simple tabulation results.
Table 2.5.5 Summary of Simple Tabulation Results of All Respondents (source:JET)
Item Content ・ Impartial responses were obtained from whole Mauritius. ・ Impartial responses were obtained from each age and sex. ・ Length of residence: 30% were 11-30 years and 31-50 Basic Information years ・ Land ownership of the residents: Over 85% of respondents own land and house ・ Recognition of landslide: 70% of respondents knew of Awareness about landslides landslide disaster and ・ Method of information acquisition about landslides: main experience responses were TV, radio, newspaper, word of mouth ・ About 60% of respondents do not know about the existing early warning system. ・ Needs of warning system: 97% of respondents need the Recognition about the warning system early warning system ・ Necessary information for warning system: Evacuation sites, Hazardous spot around your residence, Timing of evacuation, Evacuation route ・ 86% of respondents know the existing development/building restrictions Recognition about the ・ Method of information acquisition about restrictions: Word development/building of mouth, TV, radio, newspaper restrictions ・ Recognition of development restriction in slope area: About 75% of respondents know the restrictions. Establishment of the ・ About 97％ of respondents agree to the establishment of landslide caution zone the landslide caution zone Hazard map ・ About 97% of respondents agree to publicity of hazard map ・ Needs of development/building restriction and advice for building by Local Authority: About 95％ of respondents agree to the restriction and regulation Restriction in the ・ Relocation from the caution zone to safe area: About 90% landslide caution zone of respondents agree to the relocation. ・ Assistance for relocation by government: Main responses were financial assistance, to secure alternative land and to secure alternative house ・ Evacuation action in landslide occurrence: Main responses were to report the situation to the Authority, evacuate voluntarily, evacuate with family/neighbors at Evacuation exercise recommendation of Authority ・ About 90% of respondents are aware of participation to the evacuation drill/exercise
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The following table shows the summary of simple tabulation results of questions about development restrictions and relocation.
The respondents at all pilot sites approve of the development restrictions and relocation. The three districts are positive regarding development restrictions and relocation, but different levels of positive awareness about the development restrictions and relocation are confirmed as shown in the following table.
Table 2.5.6 Comparison of Awareness in the Three Pilot Sites (source:JET)
Development restrictions Relocation ・ The majority have opinion of ・ The majority have opinion of Chitrakoot “Agree” “Agree”/“Strongly agree” with or without assistance by government ・ The majority have opinion of ・ The majority have opinion of “Strongly Quatre “Strongly Agree” agree” with or without assistance by Soeurs government ・ Generally “Agree” ・ Generally “Agree” ・ The residents have the lowest ・ 10-20% residents have opinion of percentage of “Strongly “Disagree”/“Strongly Disagree” Agree” of the three pilot sites ・ The percentage of “Agree”/ “Strongly Vallée Pitot Agree” is increased by government assistance ・ The residents have the lowest percentage of “Strongly Agree” of the three pilot sites
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2.6 Organizations and Systems
2.6.1 Organizational and Institutional Formation
The Government of Mauritius designates the responsibilities of the natural disaster management to the several ministries and organizations. In terms of landslide disaster management, seven ministries and 11 organizations share the roles and responsibilities according to the ‘National Disasters Scheme 2014’.
a. Main Authorities of the Disaster Management
The Cyclone and Other Natural Disasters Committee, which is composed of 21 ministries, nine local authorities and 14 public-private organizations, had functioned as the main body of the general disaster management for over thirty years14. However, it was replaced by a National Disaster Risk Reduction and Management Council in October 2013. According to the National Disasters Scheme 2014, the National Disaster Risk Reduction and Management Council is responsible for coordination of all stakeholders in order to implement the disaster risk reduction policies and strategies, and to promote effective disaster risk management. Together with the National Disaster Risk Reduction and Management Council, a National Disaster Risk Reduction and Management Centre (NDRRMC) has been set up under the Prime Minister’s Office (PMO) to develop a disaster risk reduction strategy and plan at all levels. While the NDRRMC is a permanent body, an Emergency Operations Command (EOC) will be activated under the NDRRMC when a serious disaster occurs. A Crisis Committee will also be operated depending on the magnitude and severity of the disaster and will supervise the disaster response operations, decide the disaster response measures and issue evacuation orders. In addition, Local Disaster Risk Reduction and Management Centres (LDRRMC) have been established to coordinate all disaster risk reduction and management activities in their respective areas as well as to conduct an annual simulation exercise for tsunami/high waves, torrential rain and landslides15. (Table 2.6.1)
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Table 2.6.1 Main Authorities of Disaster Management (source: JET)
Organization Type and members General missions for disaster management National Disaster Risk Reduction Permanent Replacing the responsibilities of the and Management Council (Council) The Council consists of: CONDC in October 2013 - The Secretary to Cabinet and Head of the Civil Service The Council is responsible for - The Financial Secretary; coordinating the implementation of:- - The Supervising Officer of the Prime Minister’s Office; (1) The National Risk Reduction and - The Commissioner of Police; Management Policy approved by - The Supervising Officer of the Ministry responsible for the subject of public utilities; the Minister. - The Supervising Officer of the Ministry responsible for the subject of Environment; (2) The National Disaster Risk - The Supervising Officer of the Ministry responsible for the subject of local Reduction and Management government; Strategic Framework and Plan - The Supervising Officer of the Ministry responsible for the subject of public developed by the National Disaster infrastructure; Risk Reduction and Management - The Supervising Officer of the Ministry responsible for the subject of social security; Centre (NRDDMC); - The Supervising Officer of the Ministry responsible for the subject of social welfare Promoting safety and resilience at all centres; levels by utilizing knowledge, - The Island Chief Executive, Rodrigues; innovation and education; and - The General Manager, Outer Islands Development Corporation; Coordinating the implementation of the - The Chief Fire Officer, Mauritius Fire and Rescue Service; obligations of the State of Mauritius - The Director, Mauritius Meteorological Services; under disaster management treaties. - A representative of the Mauritius Employers’ Federation; - A representative of the Joint Economic Council; - A representative of the Mauritius Red Cross Society; and - 2 representatives from other non-governmental organisations, to be appointed by the Minister. Prime Minister’s Office (PMO) National Disaster Risk Permanent Planning, organizing, coordinating and Reduction and Management monitoring of disaster risk reduction and Centre (NDRRMC) management activities at all levels Developing a disaster risk reduction and management strategy Emergency Operation Occasional Being responsible for coordination Command (EOC The EOC consists of the representatives from the following organisations: during the preparedness, response and - Ministries/Departments; recovery phases of any disaster; - Other emergency services; - NGOs - Private sector companies Crisis Committee Occasional (depending on the magnitude and severity of a disaster) Supervising the organisations which The Crisis Committee consists of: undertake disaster response
2-39 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. - The Secretary to Cabinet and Head of the Civil Service, who shall be the operations; chairperson; Taking appropriate measures in order - The Commissioner of Police to provide effective relief assistance; - The Director-General of the NDRRMC; and and - Such other person as the chairperson of the Crisis Committee may determine. Issuing evacuation order. Government Information Permanent Being a communications hub of the Service (GIS) Government; Disseminating accurate information in a timely manner, with a view to stimulate public support; Providing information to the government in order to facilitate decision making; and Acting as the interface between the government and the local/international media. Local Disaster Risk Reduction and Permanent Coordinating all disaster risk reduction Management Committee The LDRRMC consists of: and management activities within their (LDRRMC) - The Lord Mayor of a Municipal City Council, Mayor of a Municipal Town Council or respective areas of jurisdiction; Chairperson of a District Council; Conducting an annual simulation - A representative of the Ministry responsible for the subject of public infrastructure; exercise for tsunami/high waves, - A representative of the Ministry responsible for the subject of social security; torrential rain and landslide in their area - A representative of the Ministry responsible for the subject of environment and of jurisdiction; sustainable development; - A representative of the Ministry responsible for the subject of education; - A representative of the Ministry responsible for the subject of local government; - A representative of the Ministry responsible for the subject of social welfare centres; - A representative of the Mauritius Meteorological Services; - A representative of the Mauritius Police Force; - A representative of the Mauritius Fire and Rescue Service; - The Chief Executive of the Municipal City Council, Municipal Town Council or District Council; - The assistant Chief Executive of the Village Council; - A representative of the Central Electricity Board; - A representative of the Central Water Authority; - A representative of the Road Development Authority; - A representative of the Wastewater Management Authority; - A representative of the Water Resources Unit of the Ministry responsible for the subject of public utilities; - A representative of the Mauritius Red Cross Society. Reference: Prime Minister’s Office (2014) ‘National Disasters Scheme 2014’.
2-40 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. 15 b. Organizations of Landslide Disaster Management
The task of landslide monitoring was previously undertaken by the National Development Unit (NDU). It has been transferred to the Landslide Management Unit (LMU) which was established in the Civil Engineering Section in the Ministry of Public Infrastructure (MPI) in September 2009.
In line with the LMU, the table below shows the other main organizations which are responsible for landslide disaster management.
Table 2.6.2 Main Ministries and Organizations in Charge of Landslide Disaster Management (source: JET)
Organization Organizational General missions relating to landslide disaster type management Ministry of Public permanent National Development Unit (NDU) Infrastructure, and Land - Conducting site survey Transport (MPI) - Responsible for large scale river disasters Landslide Management Unit (LMU) - Enhancing capacity of landslide monitoring - Conducting site survey - Responsible for large scale landslide disasters Road Development Authority (RDA) - Conducting site survey - Responsible for large scale disasters on the road National Disaster Risk permanent Gathering information relating to landslide Reduction and disasters Management Centre Coordinating all related stakeholders when NDRRMC) landslide disaster occurs Issuing national disaster scheme Police permanent Provides warning to all inhabitants based on information from NDRRMC Supporting evacuation of inhabitants Mauritius Meteorological permanent Providing rainfall data Service (MMS) Local Authorities permanent Conducting site survey with MPI/LMU, MPI/NDU and MPI/RDA monitoring Ministry of Housing and permanent Updating the Planning Policy Guidance (PPG) Land (MHL) Ministry of Health and permanent Preparing medical and para-medical staff, special Quality of Life (MHQL) ward and ambulances Ministry of Social permanent Providing emergency shelters Security, National Solidarity and Reform Institutions Ministry of Gender permanent Providing emergency shelters Equality, Child Development and Family Welfare Ministry of Education permanent Closing all educational institutions in the affected and Human Resources areas Ministry of Information permanent Establishing the effective ways to disseminate and Communication information to the public with the collaboration of Technology Mauritius Telecom and other mobile operators Government Information permanent Preparing illustrated posters and film strips to Service (GIS) inform the dangers of landslide to the public Mauritius Fire and permanent Assisting evacuation if requested by the NDRRMC Rescue Service
2-41 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. Central Water Authority permanent Closing the valves on the pipelines in the landslide (CWA) affected areas Supplying water to the emergency shelters Reopening the valves in the reconstruction phase Central Electricity Board permanent Cutting off the power supply in the landslide affected areas Resupplying electricity in the reconstruction phase Mauritius Broadcasting permanent Broadcasting the warning in emergency situations Corporation (MBC) Mauritius Red Cross Permanent Assisting evacuation if requested by the NDRRMC St. John Ambulance Permanent Assisting evacuation if requested by the NDRRMC Reference: Prime Minister’s Office (2014) ‘National Disasters Scheme 2014’
Table 2.6.3 Main Ministries and Organizations in Charge of Landslide Disaster Management for Ordinary and Emergency Situations (source: JET)
MPI NDRRMC Police MMS Local Authorities MHL MHQL Institutions Ministry of Social Security, National Solidarity and Reform WelfareFamily Ministry of Gender Equality, Child Development and Ministry of Education and Human Resources Ministry of Information and Communication Technology GIS Service and Rescue Mauritius Fire Central Water Authority (CWA) Board Central Electricity MBC Cross Mauritius Red St. John Ambulance
Monitoring and General Preparedness Stage I Emergency Stage II situation Stage III * ■: The organizations with the responsibilities in the ordinary and emergency situations Reference: Prime Minister’s Office (2014) ‘National Disasters Scheme 2014’
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2.7 Economic Survey
2.7.1 National Economic Indicators
The population of the Republic of Mauritius was estimated to be 1,296,303 in 2013, showing a growing rate of 0.4 % since 2012. In 2013, the population aged 0 to 14 years comprised 20 % of the total population. The population aged 15 to 64 years and that aged over 65 years comprised 71 % and 9 %, respectively of the total population16.
According to the Statistics Mauritius under the Ministry of Finance and Economic Development (MoFED), Mauritius marked unemployment ratio of 9.6 % in 2006 which was the highest over the past 30 years. Although the ratio decreased to 7.2 % in 2008, it has increased since then and reached 8.1 % in 201217.
The Gross Domestic Product (GDP), GDP per capita and GDP growth in Mauritius are summarized in the following table.
Table 2.7.1 GDP, GDP Per Capita and GDP Growth18
Item 2010 2011 2012 2013 GDP (current 9,718,331,363 11,252,405,860 11,442,063,228 11,938,403,909 US$) GDP per capita 7,587 8,750 8,862 9,210 (current US$) GDP growth 4.1 3.9 3.2 3.2 (annual %)
According to the World Bank, Mauritius has shown steady improvement in economic growth in which annual GDP growth ratio is over 3 %. The World Bank also states that Mauritius has solid economic fundamentals: open to Foreign Direct Investment (USD 360 million and 3.4 % of GDP in 2012), export oriented (USD 6 billion and 55 % of GDP in 2012), high standards of governance (52nd in the 2013 Transparency International Corruption Perceptions Index) and business friendly (the top-ranked African country in business climate, ranked 20th globally in the 2014 World Bank Doing Business report).
The economy of Mauritius is known as a ‘four-pillar’ economy: sugar, textiles, tourism and financial services. The four-pillar economy makes the country less vulnerable to economic volatility and accelerates economic growth by competitiveness and strong measures. The significant factors of each sector are as follows. Sugar cane plantation remains as an important sector in terms of its share in exports in which exporting sugar in 2012 increased by 3.5 per cent compared to 201119. In terms of tourism, the growth rates of its industry are 11.5 per cent in August 2013. As financial services are the most productive sector in Mauritius, a Special Fund of 50 million rupees is provided in order to enlarge the business market and to enhance reputation of Mauritius as an international financial center20.
Inflation rate in Mauritius kept almost less than 10 % for the period of 1992-2013. The rate from 2006 to 2008 was approximately 9 % which was relatively high over the past 30 years21. However the recent rates between 2010 and 2013 vary from around 3 % to 6.5 %: inflation rate of 2.9 % in 2010, 6.5 % in 2011, 3.9 % in 2012 and 3.5 % in 201322.
2-43 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. Revenue and expenditure of the Government of Mauritius has been increasing: revenue in 2010 was 65 billion Mauritius rupees whereas 78 billion Mauritius rupees in 2013. On the other hand, expenditure in 2010 was 75 billion Mauritius rupees and 91 billion Mauritius rupees in 201322.
The budget deficit in 2013 is estimated at 3.7 % of GDP and 97 % of deficit is because of investment expenditure. Public sector debt is 54.8 % to GDP ratio and the Government of Mauritius targets 50 % of debt to GDP ratio by 201823.
2.7.2 National Economic Policies in Mauritius
Mauritius embarked on a multi-sector reform agenda in 2006 with the objective of improving the competitiveness of the economy. This reform had a considerable success in accelerating the rate of growth, reducing unemployment and speeding up the pace of diversification of the economy through the development of new sectors. The reform created fiscal space to allow the authorities to perform a comprehensive, well-targeted, and temporary counter-cyclical policy in early 2009 to mitigate the negative impacts of the global financial crisis. The fiscal stimulus contributed to absorb the shock of the 2007/08 global crisis, which was reinforced in August 2010, with a second four per cent of GDP stimulus package to cushion the impact of a weaker euro.
Since 2010, the Government of Mauritius embarked on a second generation reform programme to continue improving the country’s competitiveness as it transits to more diversified export markets, and ensures the inclusive growth for the entire population. The key elements of this reform are the improvement of (i) delivery of public services, including the civil service and public enterprises; (ii) infrastructure development, to overcome critical bottlenecks, particularly on transportation; (iii) skills enhanced through the improved productivity; (iv) social protection to provide opportunities for vulnerable population; and (v) further liberalization of non-tariff measures to improve trade competitiveness.
The introduction of Programme-Based Budgeting (PBB) by the Ministry of Finance and Economic Development (MoFED) has been a major step forward in modernizing the budget management and improving the budget process in Mauritius. While the general architecture of the PBB reforms is largely in place, the focus now is to gradually consolidate and deepen the reforms in order to reap the benefits of aligning the resource allocation with the policy priorities.
As a result of introducing the PBB, greater transparency and accountability has been engendered in the use and control of public funds. Indeed, it is expected that the PBB will increasingly be used in the public sector as a strategic management and decision-making tool to ensure more efficient and effective delivery of the public services.
In the short term, as a part of the efforts to improve the budgeting process and the general public finance framework, work in the following areas will be undertaken:
(i) the development and drafting of two major pieces of new legislation, for example, (a) the Public Finance Management Bill and (b) the Public Audit Bill which will further entrench accountability and transparency in the use of Public Funds;
(ii) Strengthening the link between planning and budgeting by encouraging Ministries to set
2-44 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. up Planning and Implementation Units (PIU) wherever applicable. The basic objective is to inculcate and enhance a culture of planning in a strategic manner which also means taking into account available financial and human resources at the disposal of a Ministry/Department while elaborating a plan for the delivery of public services. The key here is to ensure that whatever is planned will actually have a good chance of being implemented;
(iii) Further improvements in programme designs and performance indicators;
(iv) designing and implementing a PBB and related capacity building program that will provide for ongoing in-service training for public sector stakeholders, so as to broaden the understanding of PBB knowledge and as well as increase awareness of the benefits of its use as a strategic management tool;
(v) The implementation of a project to automate the budget process that will enhance budget preparation and expenditure analysis;
(vi) Further refinements to our procurement system as necessary complementary reforms to support the PBB and to ensure that blockages and bottlenecks in the procurement process are addressed so that the right balance between speed and transparency is achieved in project implementation;
(vii) Setting up of a Project Design and Monitoring Unit at MoFED to ensure value for money in project development and implementation;
(viii) developing further the Treasury Accounting System (TAS) to include reporting of nonfinancial data so as to improve monitoring and reporting in government; and
(ix) Linking the PBB framework with the on-going implementation of the Performance Management System (PMS).
Also at another length, the process of linking fiscal policy and the medium-term expenditure framework (MTEF) to strategic planning with credible expenditure ceilings that have a bearing on budget estimates will be further improved. The front-end of the overall budget process will be progressively strengthened to:
(i) Produce a full fiscal framework that integrates revenue, debt, deficit and expenditure policies with the fiscal strategy driving the determination of expenditure ceilings and
(ii) Enhance the linkages between policy priorities and resource allocation by ensuring early policy prioritization.
It is also envisaged that an assessment will be undertaken of the Public Financial Management (PFM) systems, processes and institutions using the Public Expenditure and Financial Accountability (PEFA) methodology. The assessment will: i) provide an up-to-date quantitative and qualitative assessment of the PFM framework; ii) inform a government review of its performance, which is ongoing.
PFM reform programme through comparison with a baseline PEFA assessment undertaken in 2007; iii) be a key input to the design of further PFM reform activities and iv) provide the fiduciary and procurement review necessary for Government to discuss with developing
2-45 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. partners further cooperation for PFM reform.
There will be considerable efforts to improve ministry-wide strategic planning processes including plans that are aligned with the annual budget process. Whilst there are no reasons to duplicate the planning function in cases where they exist, the added purpose of revamping planning is to facilitate cross Ministry planning processes and support management so that plans and budgets are better linked in order to deliver on services. Moreover, as the quality of the plans improves over time, management will be in a better position to evaluate competing policies and programmes and their financial implications (investment, recurrent, manpower, etc) and allow for appropriate analyses to assist decision making by policy makers.
In addition to the PBB, new approaches have been introduced in order to improve the public expenditure management since 2013. For instance, the ministries prepare three year budget plan based on the long term outcomes and indicators as well as medium term action plans, the legislative framework for public expenditure management has been enhanced, a risk management strategy has been developed and a monitoring/evaluation system for budget execution has been established24.
2.7.3 Fiscal Policy for 2014
The Government of Mauritius sets the economic and social policies for Budget 2014 in order to achieve its goal of pursuing economic prosperity as well as social well-being.
a.1 Policies to enhance further investment and economic growth
The Government of Mauritius aims at strengthening the following in order to enhance further investment and economic growth.
Stabilization of macro economy and promotion of economic development.
Public investment: Investing in infrastructure of airports and seaports which enables to increase the movement of goods, services and people, and widen the economic activities.
Supporting the traditional economic sectors and developing the new economic architecture: Together with continuous support for the traditional sectors of tourism, financial services and agro industry, new economic pillars such as ocean and renewable energy are enhanced.
Supporting the Small and Medium Enterprises (SMEs): The Government provides the favorable measures including introduction of SMS financial schemes and loans to SMEs without guarantee.
Human resource development: As human capital is recognised as a high-impact accelerator to economic growth and social well-being, 14.8 billion Mauritius rupees are allocated to the education sector to support pre-primary schools, primary schools, secondary and tertiary education, and lifelong learning.
Improvement of working environment: The Government provides the comfortable working environment with consideration of wages, safety and health of the domestic and foreign workers.
2-46 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. Enhancement of public sector: The Government of Mauritius aims at improving accountability and performance management of the public institutions in order to seek the most effective and efficient manners to deliver public services to the citizens.
a.2 Policies to further enhance modern, inclusive and caring society
The policies focusing on social security in 2014 are as follows:
Modernizing health care system: The Government of Mauritius provides 9.2 billion Mauritius rupees for the public health care in 2014 which will be used for training and recruiting health care personnel, reducing two major killer diseases of diabetes and cancer, and building the hospitals.
Natural disaster risk reduction: Based on the fact that the greater impact of natural disasters have occurred recently, the Government allocates budget for developing institutions such as a fully staffed National Risk Reduction and Management Centre, providing IT based early warning and emergency alert system, funding for emergency work and recruiting human resources.
Consolidating the social safety nets: The Government of Mauritius strengthens the social safety nets to support the vulnerable people, for example, increasing pensions for elderly people as well as social and benefits for children, and providing budget for vulnerable families living below the Poverty Intervention Line, people with disabilities and women at risk including domestic violence.
Promoting sports and culture: sports and cultural facilities are constructed and upgraded, and musical instruments are provided.
Improvement of living conditions: The Government provides budget for housing programmes for improving living conditions, changes the conditions on loans, and provides social housing.
Improvement of public services: As government’s rapid and efficient services for the public are required, the Government allocates 200 million rupees for improving the procedures with maximum use of technology.
Increase of consumption: The Government of Mauritius stimulates the economy through increasing consumers’ purchasing power with the improvement of their earning capacities, creation of higher productivity jobs and VAT refund for certain products.
Maximizing the development potential of Rodrigues and Agalega: Investment on tourism and social economic development are enhanced.
2.7.4 Fiscal Policy of the Ministry of Public Infrastructure (MPI) 2014-2016
Based on the Programme Based Budgeting (PBB), the Ministry of Public Infrastructure and Land Transport (MPI) set a strategic direction for the next three years as follows (quoted from the ‘Budget Speech 2014’25):
Adoption of an Improved Road Maintenance Programme on a performance based approach to ensure preservation of the road network and to improve road safety,
2-47 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. mobility and connectivity.
Introduce the Light Rail Transit System to provide an alternative mode of public transport, and to support a more efficient and modern inland transportation service.
Incorporation of sustainable design and construction principles, practices and norms to ensure alignment with the Maurice Ile Durable strategy.
Improve road safety through introduction of appropriate road safety devices and regular Road Safety Audits.
Decentralise and privatise vehicles examination service.
Integrate and harmonise the functions of drain construction, maintenance and cleaning through creation of a National Drainage Agency.
Improve community facilities by constructing and upgrading social and sports infrastructure in line with the Maurice Ile Durable strategy.
The financial resources by programmes and sub-programmes for MPI for 2014-2016 are shown in the table below.
Table 2.7.2 Budget for the MPI25
2014 2015 2016 Code Programmes and Sub Programmes estimates planned planned 321 Policy and Strategy Development for 146,790,000 149,090,000 151,875,000 Public Infrastructure ,Land Transport and Maritime Services
322 Construction and Maintenance of 561,694,000 529,310,000 529,277,000 Government Buildings and Other Assets
32202 Design and supervision of the 156,616,000 165,641,000 168,991,000 construction of Building and related Infrastructure
32203 Maintenance, Repairs and 300,848,000 254,259,000 248,945,000 Rehabilitation of Buildings and Other Assets.
32204 Design, Construction and 109,410,000 104,230,000 111,341,000 Maintenance of Electrical Systems in Public Buildings (ESD)
323 Construction and Maintenance 912,000,000 1,197,200,000 1,372,400,000 of Roads and Bridges
32301 Construction and Rehabilitation of - - - Roads and Bridges
32302 Maintenance of Roads and - - - Bridges
324 Land Transport Management 1,464,989,000 1,404,934,000 1,413,838,000
32401 Road Transport Management 1,258569,000 1,257,364,000 1,250,730,000
32402 Traffic Management and Road Safety 207,420,000 147,570,000 153,108,000
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325 Maritime Safety and 91,376,000 72,681,000 71,426,000 Development
404 Community-Based 441,702,000 341,594,000 334,257,000 Infrastructure and Public Empowerment
405 Land Drainage and Watershed 430,217,000 317,001,000 242,213,000 Management Total 4,049,768,000 4,011,810,000 4,115,286,000
2.7.5 Budget for LMU
The annual budget for the LMU from 2015 to 2017 is shown in the following table.
Table 2.7.3 Budget for the LMU from 2015 to 2017 (source: JET)
Classificati Item on of 2015 2016 2017 Disaster Vat component for Countermeasure
Construction Works Chitrakoot (Block A) - Section 1 Landslide 2,250,000 Consultancy Services for
Countermeasure Construction Works Chitrakoot (Block A) - Section 2 landslide 400,000 Vallee Pitot (near Eidgah) landslide 450,000 Morcellement Hermitage, Coromandel Slope failure 250,000 Damage of L'Eau Bouillie 250,000 embankment Pailles access road to Les Guibies and Slope failure 350,000 along motorway, near flyover bridge Pailles Soreze region Slope failure 500,000 Stream Riviere des Anguilles, near the bridge 450,000 erosion Post Relocation Works at Quatre Soeurs, Marie Jeanne, Jhummah Streert, Old landslide 250,000
Grand Port Stream Piper Morcellement Piat 150,000 erosion Damage of Temple Road, Creve Coeur 100,000 wall Stream Congomah Village Council (Ramlakhan) 100,000 erosion Damage of Congomah Village Council (Leekraj) 100,000 wall Damage of Congomah Village Council (Frederick) 100,000 wall Congomah Village Council (Blackburn Damage of 100,000 Lanes) embankment Les Mariannes Community Centre (Road Slope failure 100,000 area) Les Mariannes Community Centre Stream 100,000 (Resident area) erosion Stream Le Pouce Street 100,000 erosion Damage of Justice Street (near Kalimata Mandir) 400,000 wall Stream Pouce Stream 300,000 erosion
2-49 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. Pailles access road Morcellement des Stream 150,000 Aloes from Avenue M.Leal (on hillside) erosion Plaine Champagne Road, opposite Slope failure 100,000 "Musee Touche Dubois" Chamarel near Restaurant Le Chamarel Damage of 100,000 and Road Side embankment Baie du Cap: (i) Near St Francois Debris flow 100,000 d'Assise Church Bambous Virieux, Rajiv Gandhi Street Slope failure 100,000 (near Bhavauy House), Impasse Bholoa Trou-Aux-Cerfs Slope failure 100,000 Stream River Bank at Cite L'Oiseau 100,000 erosion Stream Louis de Rochecouste (Riviere Seche) 100,000 erosion Stream Montee S, GRNW 100,000 erosion Chitrakoot (Block B) Landslide 400,000 Construction on countermeasures Chitrakoot (Block A) - Section 2 Landslide 8,000,000 Vallee Pitot (near Eidgah landslide 9,000,000 Maconde Region Baie du Cap - Phase 2 Rock fall 10,000,000 Damage of Boulevard Victoria, Montagne Coupe 7,000,000 wall Chitrakoot (Block B) Landslide 6,000,000 Damage of L'Eau Bouillie 5,000,000 embankment Pailles: (i) access road to Les Guibies Slope failure 7,000,000 Pailles: (iii) Soreze region Slope failure 3,000,000 Stream Riviere des Anguilles, near the bridge 9,000,000 erosion Stream Piper Morcellement Piat 3,000,000 erosion Will be decided Damage of Temple Road, Creve Coeur based on wall the detail survey Remote Monitoring System Chitrakoot, Vallee Pitot, Quatre- Soeurs and Landslide 7,000,000 La Butte Consultancy Services for Investigation Old Moka Road, Camp Chapelon Landslide 575,000 Candos Hill, LallBahadoor Shastri and Landslide 125,000 Mahatma Gandhi Avenues Consultancy Services for Preparation of 1,500,000 2,000,000 1,500,000 Hazard Maps Consultancy Fees for Expert on Retainer 2,500,000 2,500,000 1,000,000 Basis Overtime Work for LMU 1,200,000 1,200,000 1,200,000 Maintenance and Repairs of Equipments 1,000,000 1,000,000 1,000,000 TOTAL 55,650,000 40,100,000 44,700,000 Reference: interview survey with MPI/LMU
Among the programmes and sub-programmes mentioned above, budget for Programme 322 “Construction and Maintenance of Government Building and Other Assets” has been secured in connection with the Repair and Rehabilitation Unit (RRU) in the Civil Engineering Section. The Repair and Rehabilitation Unit is attached to the Landslide Management Unit.
2-50 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. Sub-Programme 32203: Maintenance, Repairs and Rehabilitation of Buildings and Other Assets
Priority Objectives: • Ensure the useful life of government buildings and other assets is enhanced through proper rehabilitation and regular maintenance Major Services: • Maintenance of Government buildings is carried out according to standards25
Reference for Chapter 2
1 Wikimedia Commons 2 Directorate of overseas surveys (UK) (1962): Soil Map of Mauritius, Public Works and Survey Department, Port Louis Mauritius 3 Foundation of Technical Center of Landslide and Sabo, Vol.64 P.5 4 Dep. of Energy HP 5 Cyclone and Other Natural Disasters Scheme, 2010-2011 6 Port Louis City, Plan and Investigation for Landslide countermeasures , Finals report - summary, JICA, 1990 7 Ministry of Public Infrastructure Land Transport and Shipping (2011): Geotechnical Report for Suspected Landslide at Quatre Soeurs 8 Dr. A. Chan Chim Yuk, Faculty of Engineering, University of Mauritius (2006): Monitoring of Geotechnical Works at the Site of the La Butte Landslide 9 2010 Land use map of Mauritius, 2010, Mauritius Sugar Industry Research Institute 10 Housing and Population Census, 2000, Central Statistical Office (under the aegis of the Ministry of Finance & Economic Development), Mauritius 11 Poverty statistics, 2006, Central Statistical Office (under the aegis of the Ministry of Finance & Economic Development), Mauritius 12 The School Atlas of Mauritius, 2012, A. Cader Kalla, Osman Publishing 13 V. Proag, Water resources management in Mauritius, 2006, European Water 15/16 14 Prime Minister’s Office (2011) ‘Cyclone and Other Natural Disasters Scheme 2010-2011’, Ministry of Environment and Sustainable Development (MoESD) (2012) ‘Disaster Risk Reduction Strategic Framework and Action Plan for the Republic of Mauritius’ MoESD (2009) ‘Report on The Status of Laws and Institutions to Protect Environmentally Sensitive Areas in Mauritius’ Interview survey by JICA Expert Team 15 Prime Minister’s Office (2014) ‘National Disasters Scheme 2014’ 16 World Bank (2014) ‘Population data’
2-51 Chapter 3
Landslide Management Plan 1 (Survey and Results)
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3 Landslide Management Plan 1 (Survey and Results)
3.1 Landslide Hazard Area In consideration of requests from Mauritius, three high priority landslide hazard areas were selected through consultations with C/P, along with the results of the basic survey and the landslide management plan. The following was taken into consideration when selecting the priority areas:
・Areas that scored highest in the site reconnaissance landslide hazard evaluation are to be prioritized,
・MPI’s requests are given consideration, and
・From the viewpoint of technology transfer, several different landslide sizes are to be chosen where possible (recommendation from advisory committee in Japan).
The high priority landslide hazard areas chosen are: Chitrakoot, Quatre Soeurs, Vallee Pitot
Chitrakoot area: Active large-scale landslide (L=1,500m, W=700m). Because more than 10 houses have been damaged, immediate measures are expected. MPI has requested an investigation and measures.
Quatre Soeurs area: Active middle-scale landslide (L=350m, W=400m), because several houses have been damaged, immediate measures are expected. MPI has requested an investigation and measures.
Vallee Pitot area: Active small-scale landslide (L=35m, W=20m). Because three houses have been damaged and were reported in a newspaper, immediate measures are expected. This is a typical example of a landslide that is affecting urban development.
3-1 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. Table 3.1.1 Results of Landslide Hazard Area Selection (source: JET)
Selection criteria Score of landslide Request Area name Landslide Result Summary hazard from size evaluatio MPI n Landslide Hazard Area Large Active large-scale landslide scale (L=1,500m, W=700m). Because more Chitrakoot, Vallee 6 Request (L=1500 than 10 houses have been damaged, des Pretres ○ m, immediate measures are expected. W=700m) MPI has requested an investigation and measures. Landslide Hazard Area Active small-scale landslide (L=35m, Small W=20m). Because three houses have Vallee Pitot (near No- scale been damaged and were reported in 6 Eidgah) request (L=35m, ○ a newspaper, immediate measures W=20m) are expected. This is a typical example of a landslide that is affecting urban development. Middle Excluded Mgr. Leen Street The countermeasure was done with No- scale and vicinity, La 5 the support of Japan. Because it is request (L=350m, Butte now quite stable, the urgency of W=600m) measures is low. Excluded Deformation by landslide was Middle confirmed but the movement is Old Moka Road, No- scale slower than in Chitrakoot and Quatre 3 Camp Chapelon request (L=200m, Soeurs and is not affecting W=100m) surrounding houses. Further observation is necessary although the urgency of measures is low. Landslide Hazard Area Middle Active middle-scale landslide Quatre Soeurs, scale (L=350m,W=400m), Because several Marie Jeanne, 6 Request (L=350m houses have been damaged, Jhummah Streert, ○ ,W=400m immediate measures are expected. Old Grand Port ) MPI has requested an investigation and measures. Candos Hill at Excluded Small Small scale. There are no houses Lallbahadoor No- scale that need protecting within the Shastri and 3 request (L=40m, landslide area. Further observation is Mahatma Gandhi W=35m) necessary, although the urgency of Avenues measures is low.
3-2 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. 3.2 Topographic Survey In order to conduct landslide investigation and analysis, small scale plan maps and cross-section-surveying data are needed. In the main investigation, cross-section surveying and creation of plan maps were performed in (approximately) the following three areas. The location maps and survey areas of the three areas are shown in Figure 3.2.1 to Figure 3.2.6.
Table 3.2.1 Table of Quantities of Survey Areas (source: JET)
No. Name Plan map (Area) Cross section Profile 1 Chitrakoot 1.8km2 (1,800m X 1000m) Cross section profile of three directions. 2 Quatre Soeurs 0.16km2 (400m X 400m) Cross section profile of one direction. 3 Vallee Pitot 0.005km2 (70m X 70m) Cross section profile of one direction.
3.2.1 Specifications
Cross-section surveying and plan map are created according to the following specifications.
a. Cross-Section Surveying
Vertical direction: Scale (1:100)
Level direction: Scale (1:100)
Equipment used: Total Station equipment
Coordinate system and standard of height: UTM40S Zone. The control point of Mauritius nearest to a survey area is used.
Measurement: measurements are taken at 5 m intervals on a section line (X,Y,Z) and also turning point position is measured.
b. Plan Map
Scale: 1:500
Contour interval: 1 m, a cross section line and benchmark are shown on the plan map.
3.2.2 Deliverables
Cross section maps and plan maps are to be created in DXF or DWG format of AutoCAD. The deliverables are as follows.
1) All the observational data and calculation result data
2) Cross section maps
3) Plan maps
4) Reports
3-3 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC.
Figure 3.2.1 Chitrakoot, Plan Map (source: JET)
Figure 3.2.2 Chitrakoot, Cross Section (source: JET)
3-4 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC.
Figure 3.2.3 Quatre Soeurs, Plan Map (source: JET)
Figure 3.2.4 Quatre Soeurs, Cross Section (source: JET)
3-5 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC.
Figure 3.2.5 Vallee Pitot, Plan Map (source: JET)
Figure 3.2.6 Vallee Pitot, Cross Section (source: JET)
3-6 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC.
3.3 Geological Survey
3.3.1 Geology of the Landslide Area
a. Chitrakoot
Chitrakoot district is situated on a low slope at the foot of the steep bedrock. The bedrock is mainly composed of basaltic lava and also other volcanic products, while it develops joints parallel to the lower slope. Furthermore, plastic to liquid state of soils are found at the foot of the lower slope where multiple springs are observed.
Photo 3.3.1 Full View of Landslide Area (source: JET) Figure 3.3.1 shows the topography and Figure 3.3.2 an aerial photograph of the target area.
Figure 3.3.1 Topographic Map of the Site Figure 3.3.2 Aerial Photograph of the Site
(source: JET) Chitrakoot district displays distinctive morphological properties of a landslide consisted of multiple sliding blocks whose boundaries are vaguely defined. The red dashed line shown in Figure 3.3.2 is the boundary of the landslides delineated from a topographic map while the red solid line shows the extent of active sliding confirmed from the field survey.
Within the active landslide boundary, deformation appears on houses and cracks have developed on retaining walls. Scarp and small vertical displacements are also observed at the
3-7 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. head of a block.
Photo 3.3.2 Scarp in Landslide Area Photo 3.3.3 Active Area of Landslide
(source: JET)
The outline of geological features at Chitrakoot by the past investigation is shown below.
・ Topsoil is very thin clayey layer varying from 30 to 70cm in thickness. ・ The second layer mainly consists of brownish highly weathered silt and clay mass containing stones and gravels: this colluvial soil develops alternating layers with frequent plastic and wet clayey layers. The thickness varies from one to several meters. ・ The following layer is a succession of brownish to light brown highly weathered basalt, with interstratified plastic clayey layers caused by weathering of old basalt. These layers may persist on 3 to 4 meters with various weathering degrees and colors. Note that yellow to brown weathered tuff with fine volcanic ash particles were occasionally found in some of the boreholes. ・ In some boreholes, 1 to 2 m thick interstratified alluvial sand and gravels were occasionally found in the colluvia and hard basaltic rocks. ・ Finally, slightly weathered and fractured basalt develops at the bottom of each borehole, which solidifies in the underneath layer. The solidified basalt can be grouped into two different types: hard and compacted basaltic conglomerate with grey to red color containing zeolithes and fine grained fractured basalts with grey to black color.
3-8 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. Table 3.3.1 Outline of Stratum1
Thickness of Type Stratum features layer (m) 0.3～0.7 Topsoil and brown silt with clay Topsoil ～ Brown and extremely wet plastic clay & 1.0 several Colluvia Colluvia: Brown silt changing to silt with gravel and plastic clay meters Weak, highly weathered multicolored basalts Weak, highly weathered basalts with red to brown in color Weathered Weak, highly weathered yellow to brown basaltic conglomerate Rock with thin brown clay layers 3.0～4.0 & Weak, highly fractured basalts with small olivines other Highly fractured basalts with olivines Weak ,highly weathered brown or red old burned topsoil Yellow to brown weathered tuff with ashes Grey to black, fine grained fractured basalts Strong, grey fractured basalt comprised of small pieces of 4 to 5cm Fine-grained, grey basalt － Rock Strong, fine-grained grey basalt moderately fractured Alluviums made up of 0.2-3cm fine-grained, brown to grey gravel Hard and compact grey basaltic conglomerate with zeolithes
b. Quatre Soeurs
According to the Geological Map of Mauritius (Figure 3.3.3), the area at the foot of the mountain are located on superficial colluvium constituted mainly of pebbles and gravels that result from the dismantling of the upper slope old basaltic lavas of the Beau Champ Mountain. The ancient formations of the Beau Champ Mountains are marked by high slopes (sloping at 48°towards the sea on the site) and relieves generated from the presence of dykes or intrusive plugs which have been cleared and shaped by weathering and erosion. The gradient of the hills is flatter on the seaward side, while on the inland side there are steep cliffs.
Figure 3.3.3 Location of the Site on Geological Map2 In the coastal region of Quatre Soeurs, beaches are composed of sand, silt and pebbly mud which originate from the mouths of multiple streams in the region. Saddul labeled the area from the estuary of Grand River located about 1km north of the site to Mahebourg as being of
3-9 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. a type D (or Old Series) coastline. The basic features of the Type D coastline include a wide continental shelf of more than 5km and the weathered mountains of Old Series that are situated in close proximity of the coastline providing an abundant load of sediments of all sizes to the coastal zone.
According to the Soil Map of Mauritius, the dominant soil type of the area is the Mountain Slope Complexes that are dark brown to reddish brown silty clays or clays. The upper slopes are covered by lithosols, which constitute the unique terrains such as rough mountains, gorges and unweathered rockland in this area.
Photo 3.3.4 Full View of Landslide Area (source: JET)
Photo 3.3.5 Road at the Toe of The Landslide (source: JET)
Geology of the project site consists of Breccias originating from old basaltic lavas and colluvial deposits with varying thickness according to depositional sequence and topographical locations.
The feature of the stratum is shown below.
3-10 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. Table 3.3.2 Features of Stratum2
Type Thickness of layer Stratum features Topsoil is generally described as firm brown gravelly medium plasticity clay with occasional roots and cobbles. This stratum Topsoil and Average 0.5m is described as very soft to firm gravelly / high to medium Fill material plasticity clay with occasional fragments of coral or roots and plastic bags. Upper Slope 1.0m The layer is generally described as soft to firm brown gravelly Colluvium Lower Slope 4.8m / high to medium plasticity clay with occasional cobbles. The layer is generally described as soft to stiff gravelly high Colluvium of 0.71～9.0m plasticity clay. Color is brown with purple, yellow, orange and Breccia grey mottles. Alluvium is generally dense, grey clayey gravel with yellowish discolorations and occasional cobbles originating from Alluvium and 0.85～2.44m moderately weathered basalt. Marine deposit is described as Marine Deposit brown with black mottles, very soft gravelly clay with high plasticity containing occasional fragments of coral. Completely to This layer is generally purple, grey or brown with yellow or Highly Weathered Average 3.0m orange mottles, soft to stiff gravelly clay with high to medium Breccias plasticity. Completely to highly weathered basalt layer is comprised of firm grey clay with high plasticity and weak to moderately weak grey or yellowish cream-colored medium-grained basalt. Highly to moderately weathered basalt is comprised of Weathered Average 4.0m moderately weak to moderately strong grey medium-grained Basalt basalt with joints in-filled with yellowish brown clay. Moderately weathered basalt is described as moderately weak to moderately strong grey fine-grained basalt. Slightly weathered basalt is described as moderately strong to strong grey fine-grained basalt. Weathered breccia is described as moderately weak purplish grey medium-grained breccia with yellowish cream Weathered discolorations. 0.2～4.0m Breccia Slightly weathered breccia is described as moderately strong to strong medium-grained olivine basalt having purplish grey color with white dots.
3.3.2 Laboratory Test
Laboratory soil tests will be conducted when the ground investigation is conducted if required. There are basically two major laboratory soil tests for determining stability of landslide, namely: 1) mechanical tests, and 2) physical tests. While mechanical testing is used to understand the strength property of slip surface which affects the result of stability evaluation, physical testing is used to review the test results and grasp the general characteristics of the ground.
Shear strength (of ground materials) decreases from its maximum state to residual state as shear deformation progresses (Figure 3.3.4). The shear strength of the slip surface in certain landslides are considered to be close to residual state because the slip surface has experienced large displacement in the past specifically for those landslides with distinctive sliding topographies and/or those that are active and have already moved extensively. Several conditions of shear strength are believed to exist such as close to the fully softened strength or intermediate strength between fully softened and residual strength according to the history of landslide movement.
3-11 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. The repeated single shear and/or ring shear strength tests are conducted for measuring the value of resistance shear strength of the slip surface (Table 3.3.3). The original status of the soil shall be maintained for the proper soil sampling.
For the purpose of mechanical test, 1) fixed piston sampler, and 2) multi-rod rotary sampler shall be used when test samples are taken from the drilling core so that the sample cores stay undisturbed. The block samples from the surface of cut surface or large diameter wells are also considered as good sampling sites.
Figure 3.3.4 An Explanatory Drawing of Peak Strength and Residual Strength3
Table 3.3.3 Application for Soil Strength and Mechanical Property Test3
3-12 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. a. Physical Test
a.1 Particle Size Analysis
Particle size distribution（ISO 17892-4）analysis is conducted to grasp the particle size distribution of the soil at slip surface. For smaller particles, in addition to screen analysis, sedimentation analysis, density analysis (density of fine-grained soils and solid particles: ISO 17892-2, ISO 17892-3), and water content analysis（ISO 17892-1）are also conducted.
Figure 3.3.5 shows the particle size distributions of soils taken from the slip surfaces of multiple landslides in Japan’s major geological zones. Higher content of clay materials are predominant in the tertiary and thermal landslides whereas higher content of sand and gravels are typically observed in crystalline schist landslides. The test samples shall be properly taken from the exact area of the slip surface. Targeting the slip surface can be difficult in some cases as the sliding layer can be extremely thin and the particle size composition may vary depending on the distance from the slip surface.
When residual strength is tested using disturbed samples, the samples are often screened using a screen with 425 microns of mesh size beforehand to compare the result with consistency properties such as liquid limit and plastic index. Hence, particle size distribution should reflect that of slip surface for the result of strength testing to be legitimate.
The information of particle size distribution is required to evaluate the adequacy of processes for choosing samples and of testing conditions such as grain size adjustment, in addition to understanding mechanical properties of slip surface based on the result of mechanical tests.
Figure 3.3.5 Typical Particle Size Distribution of Slip Surface Soil for Each Geological Zone in Japan4 a.2 Atterberg Limits
Liquid limit and plastic limit of the soil (ISO 17892-12) are tested to grasp the characteristics of consistency at the slip surface. Figure 3.3.6 shows the relation between the plastic index (IP) of slip surface clay at various geological zones and residual shear resistance angle (φr'). Although the figure only represents datasets with particle sizes smaller than 425 microns, clays containing high IP values tend to have smaller φr' value while relation with φr' distribution or IP varies by geology. The activity of soil sample (below IP/2μm particle size content) indicates the content of swelling clay minerals.
3-13 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. The test results are used along with grain particle size distribution to understand mechanical properties of layers comprising the slip surface.
Figure 3.3.6 Relation of Plasticity Index and Residual Shear Stress Angle for Various Geological Zones5
b. Test for Mechanical Properties
Mechanical testing is implemeted to grasp the shear strength which changes from peak to fully softened and residual strength according to the soil’s stress history. When conducting stability analysis, he/she needs to choose one of the status of shear strength as a parameter. Although studies have been done into which strength should be adopted for stability analysis, a clear answer has not been provided. Furtheremore, the strength of soils can also vary within the slip surface. Therefore, the results of the physical test are only regarded as references in Japan, and instead, reverse calculation method is mostly employed in practice.
Table 3.3.4 shows the testing methods appropriate for each type of shear strength. The peak strength is determined by unconsolidated tri-axial test/cyclic shear test/ring shear test of undisturbed sample. The fully softened strength is determined by mainly unconsolidated tri-axial of undisturbed sample and by minor cyclic shear test/ring shear test of slurry sample/undisturbed sample. The residual strength is measured not by unconsolidated tri-axial test but by cyclic shear test/ring shear test.
Although the sample of slip surface can realistically reproduce the strength condition of the site, it is quite difficult to set it on test device.
3-14 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. Table 3.3.4 Selection of Test Method for Type of Sample and Characteristics of Strength Obtained by Test6
b.1 Cyclic Direct Shear Test
The test is performed on three or four specimens from a relatively undisturbed soil sample. A specimen is placed in a shear box which has two stacked rings to hold the sample; the contact between the two rings is at approximately the mid-height of the sample. A confining stress is applied vertically to the specimen, and the upper ring is pulled laterally until the sample fails, or through a specified strain. The load applied and the strain induced is recorded at frequent intervals to determine a stress-strain curve for the confining stress.
Cyclic direct shear tests can be performed under several conditions. The sample is normally saturated before the test is run, but can be run at the in-situ moisture content. The rate of strain can be varied to create a test of undrained or drained conditions, depending on whether the strain is applied slowly enough for water in the sample to prevent pore-water pressure buildup.
Several specimens are tested at varying confining stresses to determine the shear strength parameters, the soil cohesion (c) and the angle of internal friction (commonly friction angle) (ϕ). The results of the tests on each specimen are plotted on a graph with the peak (or residual) stress on the x-axis and the confining stress on the y-axis. The y-intercept of the curve which fits the test results is the cohesion, and the slope of the line or curve is the friction angle.
Figure 3.3.7 and Figure 3.3.8 show the structure of a cyclic shear test device, and relation between shear stress and accumulative shear displacement. Figure 3.3.9 shows a schematic figure of a shear box that is able to measure the friction force.
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Figure 3.3.7 Structure of Cyclic Shear Test Device7
（a）undisturbed soil （b）disturbed soil
Figure 3.3.8 Relation between Shear Stress and Accumulative Shear Displacement7
Figure 3.3.9 Measuring the Friction Force between Two Shear Boxes8
Mitachi et al.(1999) proposed a method which strength values for countermeasure design are determined on c-tanφ graph based on a peak strength, a fully softened strength and a residual strength with cyclic shear test (Figure 3.3.10). Point A is a peak strength, Point B is a fully softened strength and point C is a residual strength in the figure. Point D crossing between the line A, B, C and c-tanφ line should be adopted for design in this method.
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Figure 3.3.10 Method of Determining Strength Factor for Design Using C-Tanφ Diagram9 Figure 3.3.11 shows a schematic figure of direct shear test for slip surface, which can measure the shear strength on the slip surface. The shear line in the machine is accorded along the actual slip surface.
Figure 3.3.12 shows the procedure of the sample for the direct shear test for slip surface.
Figure 3.3.11 Structure of Shear-Test Device10
Figure 3.3.12 Method of Making Test Piece That Includes Slip Surface10
b.2 Tri-Axial Shear Test
The principle behind a triaxial shear test is that the stress applied in the vertical direction (along the axis of the cylindrical sample) can be different from the stresses applied in the horizontal directions perpendicular to the sides of the cylinder, i.e. the confining pressure.
3-17 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. A solid is defined as a material that can support shear stress without moving. However, every solid has an upper limit to how much shear stress it can support. The triaxial test is designed to measure that limit. The stress on the platens is increased until the material in the cylinder fails and forms sliding regions within itself, known as shear bands. A motion where a material is deformed under shear stress is known as shearing. The geometry of the shearing in a triaxial test typically causes the sample to become shorter while bulging out along the sides. The stress on the platen is then reduced and the water pressure pushes the sides back in, causing the sample to grow taller again. This cycle is usually repeated several times while collecting stress and strain data about the sample.
During the shearing, a granular material will typically have a net gain or loss of volume. If it had originally been in a dense state, then it typically gains volume, a characteristic known as Reynolds' dilatancy. If it had originally been in a very loose state, then contraction may occur before the shearing begins or in conjunction with the shearing.
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Figure 3.3.13 Structure of Triaxial Shear Test Device3
c. Results of Past Laboratory Soil Tests
The tests shown in Table 3.3.5 below were conducted in Chitrakoot and Quatre Soeurs in the past, and soil tests as shown in Table 3.3.6 were carried out.
Table 3.3.5 Previous Survey Report (source: JET)
No Report Company GEOTECHNICAL INVESTIGATION AT CHITRAKOOT 1 SOTRAMON LIMITEE VALLEE DES PRETRES GEOTECHNICAL REPORT FOR SUSPECTED LANDSLIDE WATER RESEARCH 2 AT QUATRE SOEURS CO.LTD
Table 3.3.6 List of Laboratory Soil Tests Conducted (source: JET)
Item No Description of Test Chitrakoot Quatre Soeurs 1 Specific gravity ○ ○ 2 Natural moisture content ○ ○ 3 Atterberg limits ○ ○ 4 Particle size distribution ○ ○ 5 Unconfined compression ○ ○ 6 Shear box ○ － 7 Triaxial ○ ○ 8 Bulk density ○ ○
3-19 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. c.1 Chitrakoot
The laboratory soil test results of the past investigation are shown below.
Table 3.3.7 Results of Physical Test (source: JET)
Specific Moisture Atterberg Bulk Drilling Depth (m) Geology gravity content Limits (%) Unit Wt No. 3 3 (g/cm ) (%) LL PL (kN/m ) 2.00～2.50 Colluvium 2.790 42.0 89.0 34.0 17.84 BPP5 Highly weathered 7.00～8.00 2.780 38.0 65.0 35.0 18.20 basalt Highly weathered BPP6 7.25～7.80 2.810 52.0 58.0 39.0 16.69 basalt 4.50～5.00 Colluvium 2.780 50.0 61.0 31.0 17.37 Highly weathered 8.00～8.50 31.0 49.0 29.0 18.91 BPP8 basalt Highly weathered 12.00～12.75 2.670 52.0 54.0 30.0 17.22 basalt Highly weathered 2.60～2.93 2.640 42.6 74.0 30.0 16.61 basalt BPP9 4.10～4.54 Weathered basalt 2.780 38.0 60.0 32.0 17.48 Highly weathered 7.30～7.85 2.750 26.0 56.0 35.0 17.76 basalt 1.53～2.20 Colluvium 2.780 38.0 60.0 32.0 18.88 3.30～3.66 Colluvium 2.780 36.0 71.0 31.0 18.81 BPP13 Highly weathered 5.50～6.00 34.0 basalt BPP14 4.85～5.40 Colluvium 42.0 72.0 44.0 7.50～8.00 Colluvium 35.0 55..0 32.0 BPP15 9.00～9.50 Colluvium 27.0 59.0 30.0 3.15～3.65 Wet plastic clay 40.0 64.0 33.0 17.98 BPP16 5.00～5.50 Wet plastic clay 33.0 57.0 25.0 18.83 7.00～7.50 Weathered tuff 51.0 3.00～3.50 Colluvium 35.0 57.0 34.0 BPP18 5.50～6.00 Weathered tuff 34.0 77.0 46.0 17.88
Table 3.3.8 Results of Physical Test (source: JET)
Specific Moisture Atterberg Bulk Drilling Depth (m) Geology gravity content Limits(%) Unit Wt No. 3 3 (g/cm ) (%) LL PL (kN/m ) 8.00～8.40 Colluvium 2.820 30.0 75.0 34.0 BPI2 Highly 12.05～12.70 29.0 67.0 38.0 weathered basalt Highly BPI4 5.40～6.00 54.0 66.0 34.0 17.06 weathered basalt 3.10～3.65 Colluvium 2.800 41.0 66.0 39.0 6.00～6.50 Weathered tuff 44.0 73.0 37.0 BPI9 Highly 8.40～9.00 47.0 73.0 37.0 weathered basalt 10.00～10.56 Weathered tuff 55.0 73.0 37.0 3.00～3.50 Colluvium 29.0 63.0 35.0 Highly 4.50～5.00 45.0 70.0 45.0 weathered basalt Highly 5.50～6.00 49.0 75.0 50.0 weathered basalt BPI10 Highly 6.50～7.00 39.0 75.0 48.0 weathered basalt 8.00～8.40 Weathered tuff 2.780 36.0 82.0 46.0 17.33 9.00～9.50 Weathered tuff 38.0 65.0 46.0 Highly 10.00～10.50 27.0 58.0 38.0 weathered basalt
3-20 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. Table 3.3.9 Results of Shear Box Test (source: JET)
Shear strength parameters Moisture Bulk.U. Drilling Depth (m) Geology content Wt Peak Values Residual Values No. (%) (kN/m3) C1 φ1 C1r φ1r (kN/m2) (°) (kN/m2) (°) BPI-4 5.40～6.00 Clay and silt 39.6 17.06 11 22 14 21 BPI-10 8.00～8.40 Weathered tuff 36.9 17.33 27 25 19.5 23 Highly BPP-6 7.25～7.80 52.0 16.63 12 28 weathered basalt BPP-8 4.50～5.00 Colluvium 50.0 17.24 28.5 29 12.00～ Highly BPP-8 52.0 17.08 26 30 12.75 weathered basalt
Table 3.3.10 Results of Triaxial Compression (source: JET)
Before Moisture content Shear strength consolidation Drilling (%) parameters Depth (m) Geology Bulk.U. Dry.U. No. Wt Wt C1 φ1 Before After 3 3 (kN/m ) (kN/m ) (kN/m2) (°) Highly weathered BPP5 8.35～8.85 38.3 39.6 19.2 13.9 38.7 30.5 basalt 11.00～ Highly weathered BPP8 55.2 53.4 17.8 11.5 94.0 14.3 11.50 basalt
c.2 Quatre Soeurs The laboratory soil test results of the previous investigation are shown below.
Table 3.3.11 Results of Physical Test (source: JET)
Natural Atterberg Limits Bulk Drilling Depth (m) Geology Moisture LL PL Unit Wt No. PI 3 content (%) (%) (%) (kN/m ) 1.00～1.50 CHW Breccia 42.0 76.0 38.0 17 BH1 3.00～3.50 CHW Breccia 44.0 68.0 42.0 16 1.00～1.50 Colluvium 59.0 90.0 37.0 BH3 2.50～3.00 Colluvium 63.0 95.0 33.0 3.00～3.50 Colluvium 38.0 68.0 36.0 BH4 4.00～4.50 CHW Breccia 43.0 65.0 31.0 12.56～15.00 Alluvium 16.0 79.0 40.0 3.00～3.50 Colluvium 59.2 16.24 BH5 5.00～5.50 Colluvium 68.7 16.02 5.50～6.00 Colluvium 58.0 94.0 32.0 2.50～3.00 Colluvium 42.0 72.0 28.0 18 BH6 4.50～5.00 Colluvium 56.0 102.0 33.0 21 16.88
3-21 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. Table 3.3.12 Results of Physical Test (source: JET)
Natural Atterberg Limits Trial Linear Depth (m) Geology Moisture LL PL Pit PI Shrinkage content (%) (%) (%) Tp1 1.40 C/HWB 46.6 96.1 37.0 22.5 59.1 Tp3 2.00 HWB 38.4 62.5 33.1 16.4 29.4 Tp4 1.50 Clay 49.2 91.8 47.4 20.7 44.4 Tp5 3.00 Clay/Colluvium 37.2 69.3 34.3 19.6 35.0 1.00～1.50 Clay/Colluvium 56.1 75.0 46.2 18.6 28.8 Tp6 1.50～1.80 Clay/Colluvium 24.8 102.4 64.5 23.2 37.9
Table 3.3.13 Results of Triaxial Compression (source: JET)
Moisture Before consolidation Shear strength Drilling Depth content (%) parameters Geology Bulk.U. Dry.U. No. (m) Wt Wt C1 φ1 Before After 3 3 (kN/m ) (kN/m ) (kN/m2) (°)
3.0～ BH5 Colluvium 50.2 49.7 18.7 12.5 0.4 1.4 3.5
d. Results of the Laboratory Soil Test
The laboratory soil test results of this investigation are shown in Table 3.3.14.
Test items were to target physical testing, and the target layer of the tests was mainly surface layer colluvium. Mechanical tests could not be conducted because the soil contained too much gravel.
Table 3.3.14 List of Laboratory Soil Tests (source: JET)
Quantity Item No Description of Test Chitrakoot Quatre Soeurs 1 Specific gravity 6 2 2 Natural moisture content 6 2 3 Atterberg limits 4 2 4 Particle size distribution 6 2 5 Bulk density 2 1
d.1 Chitrakoot
The particle size distribution in colluvial soil was highest for fines, followed by gravel and sand. If the soil is common inorganic matter, the soil particle density will measure 2.6～ 2.8g/cm3. Past soil test results were also mainly in this value range. The values of the test conducted this time were in the 2.0 ～3.0g/cm3 range, a somewhat large variation.
Natural moisture content tends to be higher in fines and lower in course-grained soil. Test values were largely around 50% and correspond to those of soft clay, affected by the high degree of fine particle fraction content. Values are a slightly high compared to past soil test results.
3-22 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. The Atterberg limit is the collective term for the liquid limit, plastic limit and shrinkage limit. The deformation characteristics of clay change depending on its water content, and the water content standards are divided into 4 classifications as shown in Figure 3.3.14. The liquid limit for samples BH-C5 and BH-C4 was high and plasticity index large compared to other samples.
Figure 3.3.14 Atterberg Limits11 The density test was for only 2 samples, and the results were 1.60g/cm3 and 1.80g/cm3. These were almost the same values as in past soil tests, and the sample with high density had a high content of gravel.
The test results are charted below.
Table 3.3.15 Results of Physical Test(1) (source: JET)
Particle size distribution (%) Sample Borehole Depth (m) Geology Fines Sand Gravel Cobbles Type BH-C1 3.00～3.45 Colluvia 43.0 15.0 42.0 0 STP20
BH-C2 4.80～5.25 Colluvia 52.7 10.3 37.0 0 U2
BH-C3 6.60～7.05 Colluvia 70.0 29.0 1.0 0 U2
BH-C4 6.35～6.80 Colluvia 65.0 10.0 25.0 0 SPT28
BH-C5 4.25～4.70 Colluvia 97.0 4.0 3.0 0 SPT56
BH-C6 5.30～5.75 Colluvia 77.6 18.9 3.5 0 SPT25
Table 3.3.16 Results of Physical Test(2) (source: JET)
Particle Atterberg Limits Bulk Moisture Borehole Depth (m) density LL PL density 3 content (%) PI 3 (g/cm ) (%) (%) (g/m ) BH-C1 3.00～3.45 1.94 50.0
BH-C2 4.80～5.25 2.98 51.2 78.0 42.9 35.1 1.80
BH-C3 6.60～7.05 2.57 43.8 73.0 45.1 27.9 1.60
BH-C4 6.35～6.80 2.98 61.8 89.5 45.0 44.5
BH-C5 4.25～4.70 2.67 47.7 110.5 41.7 68.8
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BH-C6 5.30～5.75 2.10 41.3
d.2 Quatre Soeurs
The tests targeted colluvium and hard silty clay.
Particle size characteristics of the colluvial soil indicated that fines content was highest followed by gravel content. On the other hand, silty clay had a high content of gravel followed by fines.
If the soil is common inorganic matter, the soil particle density will measure 2.6～2.8g/cm3. Test results for both samples were around 2.90g/cm3, indicating the possibility they contain a high-density mineral.
Natural moisture content tends to be higher in fines and lower in course-grained soil. Natural moisture content in colluvium was 56% and over 100% in silty clay, affected by the high degree of fine particle fraction content. It was particularly high for silty clay because the sampling depth was deep and it was in a saturated state.
No major differences could be seen in the Atterberg limits for samples BH-Q1 and BH-Q2.
A density test was only conducted for one sample of silty clay, and its result was 1.58g/cm3. This is a slightly lower value than for cohesive soil.
Test results are shown below.
Table 3.3.17 Results of Physical Test (1) (source: JET)
Particle size distribution (%) Sample Borehole Depth (m) Geology Fines Sand Gravel Cobbles Type BH-Q1 1.00～1.45 Colluvia 70.0 10.0 20.0 0 STP10
BH-Q2 9.00～9.40 Silty Clay 35.5 8.5 52.0 0 U2
Table 3.3.18 Results of Physical Test (2) (source: JET)
Particle Atterberg Limits Bulk Moisture Borehole Depth (m) density LL PL density 3 content (%) PI 3 (g/cm ) (%) (%) (g/m ) BH-Q1 1.00～1.45 2.98 55.8 88.0 34.17 53.83 －
BH-Q2 9.00～9.40 2.83 105.6 86.5 35.0 51.5 1.58
3-24 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. e. Ring Shear Test Result by this Project
e.1 Outline of ring shear test
The soil sample supplied for the ring shear test was sampled while disturbed from 0.5-2.0m under the ground with a shovel and a pick for the colluvial deposit in each landslide.
After sampling, the soil samples were sealed in heat resistant polyethylene bag, and transported to Japan by airmail.
Moreover, the high-pressure sterilization processing was executed in Yokohama Plant Quarantine Stations when importing it, and transported to the laboratory.
The location where the soil samples taken and the situation photograph of the sampling are shown below.
Sampling location
Figure 3.3.15 Sampling Location (Chitrakoot) (source:JET)
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Sampling location
Figure 3.3.16 Sampling Location (Quatre Soeurs) (source:JET)
Sampling location
Figure 3.3.17 Sampling Location (Vallee Pitot) (source:JET)
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Photo 3.3.6 Sampling Situation Photo 3.3.7 Samples
e.2 Outline of ring shear test
Ring shear apparatus is classified as direct shear type as well as the direct shear testing apparatus.
However, the ring shear apparatus is a testing machine that can infinitely measure the shear displacement while giving the same strain doing rotational shear by differing from direct shearing apparatus. No垂直応力Ｎrmal stress N As a result, it is possible to obtain the せん断 residual strength of clay as shown in the 応力ＳShear stress S Figure 3.3.18. σ τ Figure 3.3.19(a) shows stress-strain curve τ in the drain shearing test by some vertical σ stress σ'.
(a)（ａ）一面せん断試験のせん断機構 Shear mechanism of One shearing test Moreover, Figure 3.3.19(b) shows that the peak strength and the residual strength are Normal 垂直応力Ｎstress N estimated by using the linear regression of shear stress under the different vertical
load. ﾄﾞｰﾅﾂ型Doughnut type 供試体 test piece In a word, the shearing test of the past was limited to the measurement of peak strength (overconsolidated clay) and complete softening strength (normally-consolidated clay) by restricting the shear displacement.
However, the ring shear test enabled the Rotational回転せん断 shear measurement of the residual strength that (b)（ｂ）リングせん断試験のせん断機構 Shear mechanism of Ring shearing test was not able to be measured by canceling displacement shortage so far.
Figure 3.3.18 Difference between Direct Shearing Test and Ring Shear Test (source:JET)
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Overconsolidation Overconsolidation 過圧密ピーク強度 過圧密ピーク強度peak strength peak strength Shear stress σ' constant 正規圧密ピーク強度Nomal consolidation Fully softened完全軟化強度 strength peak strength Residual残留強度 strengt
Residual残留強度 strength Nomal consolidation 正規圧密ピーク強度 c' peak strength ・ 0 σ' 0 Displacement Effective pressure on shear plane (a) (b)
Figure 3.3.19 Shearing Characteristic of Normally-Consolidated Clay and Overconsolidated Clay12 e.3 Test equipment
Figure3.3.20 shows structural drawing of the ring shear apparatus (main body part), Figure 3.3.21shows rough sketch of the test specimen.
Jack-up of upper shear ring
Vertical pressure meter
Load cell for wall friction measurement
Vertical pressure adjustment valve
Spherical coordinates joint
Vertical displacement sensor
Equilibrium pressure meter
Load cell for shearing torque measurement Equilibrium pressure regulator
Shearing box
Detector sensor of angle Change gear Shear
Shearing manual operation surface
Control box
Vertical load beroff lamb cylinder
Figure 3.3.20 Structural Drawing of the Figure 3.3.21 Test Specimen Rough Sketch13 Ring Shear Apparatus (source:JET)
e.4 Test method
The process of the ring shear test (the grain diameter sample of 0.425mm or less) is shown in Figure 3.3.22.
A vertical stress is changed to 300→250→200→150→100→50kPa after the residual
3-28 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. strength was confirmed, and strength parameter (cr', φr’) of the residual strength was determined.
Sampling Sampling of disturbed soil
The coarse-grained fraction is removed using 0.425mm bolter sieve after the sample is dissolved in water. Sample The sample is dried to remove the water content so that remixing is possible adjustment using a constant temperature drying oven (60°).
Pre-consolidation is conducted for the 80 percent of the test load. When a set time passes, consolidation is ended.
Preload 240kPa (7days)
Sample A disk shaped sample that completed pre- consolidation is set into the apparatus. molding After setting, it hollows to the doughnut shape and is molded into this shape.
The test load is loaded and consolidation is commenced. Consolidation is completed by 3t method.
Consolidation 300kPa
Shearing Sample is sheared 360° or more. After the residual status is confirmed, unload the test load by 50kPa step-by-step.
Figure 3.3.22 Examination Process of Ring Shear Test (source: JET)
e.5 Test condition
Number of ring shear tests ･････Three samples (for each test specimen) Size of test specimen ･････150mm in outside diameter, 100mm in inside diameter, and 20mm in thickness Shear velocity ･････0.02 mm/min Amount of the final displacement ･････360° or more Test load ･････300kPa [After confirming the residual strength,300→250→200→150→100→50kPa] Consolidation condition ･････Normal consolidation（OCR=1.0） Drain condition ･････Consolidated-drained test (CD test)
e.6 Test outcome and observations
Data of test and diagram of stress path where strength parameter is decided are included in the data sheet. Stress path diagram, which is determined the test data and strength parameters are also included in the data sheet. Table 3.3.19 shows ring shear test.
3-29 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. Table 3.3.19 Ring Shear Test Result (source:JET)
Residual shearing Sample Residual cohesion Location of sample resistance angle name Cr’（kPa） Φr’(°)
Chitrakoot S-1 18.7 11.8
Quatre Soeurs S-2 5.7 12.2
Vallee Pitot S-3 3.5 6.4
Residual shear resistance angle φr 'of Chitrakoot and Quatre Soeurs was 11.8°, and 12.2°. φr 'of Vallee Pitot was 6.4°.
The type of soil of Vallee Pitot is clayey compared with Chitrakoot and Quatre Soeur, and has the possibility of including clay minerals etc.
Residual cohesion Cr ' values have the possibility of being too high due to the test condition and influence of friction with the apparatus.
In an actual landslide stability analysis, estimation error of the slip surface shape and groundwater conditions and the influence of the resistance of the landslide periphery (edge effect) etc., and various uncertain data can exist. Therefore, it is preferable to adopt shear resistance angle φ' and to adopt c' according to back calculation.
Apparently, it is proposed to add the effects of these uncertainties in to the backcalculated c '.
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3.3.3 Water Quality Analysis
The purpose of the water quality analysis is to identify the distribution of groundwater in the survey area and to define the groundwater system (streaklines) as part of the landslide survey.
a. Survey Method
A total of 17 water quality analysis samples were collected from the following sites in two districts (Chitrakoot and Quatre Soeurs) in the survey area. The samplings were carried out at Chitrakoot on the end of March 2013 and at Quatre Soeurs. Table 3.3.20 shows the status of sampling for water quality analysis.
Table 3.3.20 Status of Sampling for Water Quality Testing (source: JET)
Location of the water sample Water temperature Situation (℃) BH-C1 23 Borehole BH-C3 25 Borehole BH-C4 26 Borehole BH-C5 27 Borehole BBP(13) 24 Existing Borehole BBP(6) 25 Existing Borehole
Chtrakoot Chtrakoot BBP(11) 24 Existing Borehole P-C1 28 Surface Water (pond) R-C1 24 Surface Water (stream) R-C2 23 Surface Water (stream) BH-Q1 29 Borehole BH-Q2 27 Borehole BH-2 27 Existing Borehole BH-3 28 Existing Borehole BH-4 29 Existing Borehole BH-5 26 Existing Borehole Quatre Soeurs Quatre Soeurs RQ-1 28 Surface Water (stream)
The borehole samples will be collected using a water trap (bailer) lowered into the borehole. The existing water source (mountain runoff) samples will be collected using a plastic bucket. The samples will be immediately transferred to polyethylene bottles and taken back to the laboratory.
b. Water Quality Analysis
The water quality analysis items are the major dissolved components of ordinary groundwater and surface water. Table 3.3.21 shows the analysis method for each item.
Table 3.3.21 Water Quality Test Method (source: JET)
Item Unit Method Water Temperature - ℃ Thermometer Total Hardness - mg/l Titration Calcium Hardness mg/l Titration
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Magnesium Hardness mg/l Titration Phenolphthalein alkalinity mg/l Titration Methyl Orange Alkalinity mg/l Titration Chloride ion Cl mg/l Titration/Ion chromatography Sulfate ion SO4 mg/l Spectrophotometry/Ion chromatography Silicic acid (Silica) SiO2 mg/l Spectrophotometry Sodium Na mg/l Atomic absorption spectrophotometry Potassium K mg/l Atomic absorption spectrophotometry
c. Groundwater Analysis Method by Water Quality Analysis To ascertain the groundwater system (streaklines) by water quality analysis, the analysis results for the major dissolved components will be arranged by graphic representation of the analysis values. More precisely, the water types will be classified using the trilinear diagram and then plotted on the geological cross-section and a hexadiagram created, and changes in the water composition will be analyzed.
c.1 Hexadiagram
Taking the meq/L concentrations provided on each side of the vertical axis as the axis, the cations will be plotted on the left side and anions on the right side, and the points will be joined with straight lines to describe a hexagonal-shaped diagram (see Figure. 3.3.23). The groundwater system categories and changes in water quality accompanying groundwater motion will be analyzed according to the shape of the diagram. The broad shape on each side of the hexadiagram shows a high concentration of the component while the narrower shape represents a lower concentration. Thus the fact that there are many dissolved components in the groundwater means that the groundwater has been flowing for a long time.
(meq/1)
Figure 3.3.23 Example of Hexadiagram (source: JET)
c.2 Results of analysis
The results of analysis by hexadiagram are as follows.
Chitrakoot
The amounts of major dissolved components in the groundwater were low at all sites. The component composition in the groundwater is about the same as that in surface water. The water temperature in the groundwater was high more than 23 ºC at all sites.
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Quatre Soeurs
The amounts of major dissolved components in the groundwater were low at these sites except for BH-4. The component composition in the groundwater is about the same as that in surface water. The water temperature in the groundwater was high more than 28 ºC at all sites. The water quality at BH-4 was high with sodium and chloride ions. It was indicated that the groundwater was contaminated with the sea water.
From these results, it was considered that the groundwater associated with the landslide action was the shallow groundwater and interlocked with rainfall.
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Figure 3.3.24 Hexadiagram in the Groundwater at Chitrakoot (source: JET)
Figure 3.3.25 Hexadiagram in the Groundwater at Quatre Soeurs (source: JET)
3-34 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. 3.4 Monitoring
3.4.1 Installation of Monitoring Devices
Landslide monitoring using various instruments is ongoing in order to monitor movements of the landslides and surrounding environment such as groundwater and precipitation.
Main purposes of the monitoring works are;- - To estimate the landslide properties such as size, depth, activity and cause. - Early warning
The monitoring works are in the following areas. Chitrakoot Quatre Soeurs Vallee Pitot
The instruments for the landslide monitoring are shown in the table below.
Table 3.4.1 Instruments for the Landslide Monitoring (source: JET)
Instrument Purpose Sensor Logger Manufacturer Location of installation Displacement of the (Installed in the Chitrakoot, Extensometer Osashi ground surface (distance SLG-100 sensor, 1 hour Quatre Soeurs, Technos between two points), interval) Vallee Pitot Displacement of the (Manual Laser distance DIST ground surface (distance operation, once Leica Quatre Soeurs meter D3aBT between two points) a month) Displacement of the subsurface (lateral TC-32K Tokyo Sokki Inclinometer KB-10HC Chitrakoot displacement from the (once a month) Kenkyujo deepest point) Deformation of the earth TCR-25 Chitrakoot, Strain gauge SKF-6070 Tokyo Denki (distortion in the ground) (once a month) Quatre Soeurs Fluctuation of the Automatic groundwater level WLG-01 Osashi Chitrakoot, DS-1 Piezomete (variation of water (1 hour interval) Technos Quatre Soeurs pressure) Groundwater level (Manual Water level (distance between the Operation, once Quatre Soeurs meter surface and the ground a month) water level) Net LG-201E Osashi Chitrakoot, Rain gauge Precipitation RS-2 (1 hour interval) Technos Quatre Soeurs
3-35 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. Extensometer Laser distance meter (manual operation)
To Monitor expansion and contraction of a wire To monitor a fixed point and a target (structure such as house wall) Inclinometer, Strain Gauges Piezometer
To monitor deformation of vertical pipes installed in the To monitor the water pressure in a borehole ground Figure 3.4.1 Basic Landslide Monitoring Techniques (source: JET)
Boreholes Piezometer BH-C1 Extensometer E-C1 Inclinometer BH-C2 Extensometer E-1 Piezometer BH-C3 Extensometer E-2 Strain Gauges BH-C4 Extensometer E-5 Strain Gauges BH-C5 total 4 Inclinometer BH-C6 Rain Gauge R-C1 total 6 total 1 Figure 3.4.2 Plan of Instrument Installation – Chitrakoot (source: JET)
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Boreholes Strain Gauges BH-Q1 Extensometer (laser) E-Q1 Strain Gauges BH-Q2 Extensometer (laser) E-Q2 Piezometer BH-5 (existing) Total 2 Groundwater level BH-2 (existing) Rain Gauge R-Q1 Groundwater level BH-3 (existing) Total 1 Groundwater level BH-4 (existing) total 6 - One rain gauge is installed out of the map Figure 3.4.3 Plan of Instrument Installation – Quatre Soeurs (source: JET)
Extensometer E-V1 Extensometer E-V2 Total 2 Figure 3.4.4 Plan of Instrument Installation – Vallee Pitot (source: JET)
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3.4.2 Monitoring Results
a. Chitrakoot
a.1 Rain gauge
A rain gauge is installed at south west of the landslide area in Chitrakoot.
During the monitoring period (26th February 2013 to 4th March 2015), much precipitation was recorded in rainy season (November to April). 450.0mm/month as the maximum monthly rainfall in the monitoring period was recorded in December 2014, and the minimum monthly rainfall in the monitoring period was 8.5mm/month recorded in September 2013. There were ten days when daily precipitation exceeded 50mm in the monitoring period.
There were three days when daily precipitation exceeded 100mm/day in the monitoring period, 30th March 2013, 21st March 2014 and 16th December 2014. On 16th December 2014, 133.0mm of rainfall within six hours and 77mm of maximum hourly precipitation were recorded. On 21st March 2014, 132.0mm/day and 50.0mm/hour were recorded.
The daily precipitation on 20th March 2013 was 106.5mm, and total precipitation of 30th and 31st March was 152.5mm. The maximum hourly precipitation in 30th to 31st was 25.5mm.
Total yearly precipitation of 2014 was 1881.5mm.
Figure 3.4.5 Result of Rain Gauge (source: JET)
Table 3.4.2 Monthly and Maximum Daily Precipitation and Maximum Hourly Precipitation (source: JET) 2013 Month 1 2 3 4 5 6 7 8 9 10 11 12 Monthly - - 244.5 115.0 35.0 47.5 23.5 65.5 8.5 97.0 233.5 41.0 precipitation
Maximum daily - - 106.5 40.5 12.0 15.0 8.5 21.5 4.0 76.0 59.0 18.5 precipitation Maximum hourly - - 26.0 4.5 4.0 7.5 3.0 8.5 1.0 21.0 25.0 9.5 precipitation
3-38 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. 2014 Month 1 2 3 4 5 6 7 8 9 10 11 12 Monthly 422.5 115.0 234.5 175.5 95.0 26.0 69.0 102.0 57.0 46.5 88.5 450.0 precipitation
Maximum daily 83.0 26.5 132.0 74.5 38.0 7.0 17.5 22.0 23.0 23.0 46.0 133.0 precipitation Maximum hourly 29.0 8.5 50.0 25.0 8.5 3.5 14.0 10.0 3.5 8.0 26.0 77.0 precipitation
2015 Month 1 2 3 4 5 6 7 8 9 10 11 12 Monthly 367.0 116.0 ------precipitation
Maximum daily 56.5 28.5 ------precipitation Maximum hourly 30.0 7.0 ------precipitation
a.2 Extensometer
E(1) is installed at the foot of Chitrakoot landslide area. Compression displacement has continued. This may represent a shallow slide at the location.
Since no deformation on the ground and the house around the location can be found but only small deformation can be seen at the base of the protection cage, the extensometer shows surface creep.
E(2) is installed at the foot of Chitrakoot landslide area. The result shows small compression and small tension alternately.
Since no deformation on the ground can be found and the ground is almost level below the location of the extensometer, the extensometer does not show big landslide. The complicated movement may show two shallow ground movements which move separately as shown Figure 3.4.7. “A” may always move continuously and “B” may move with heavy rain.
E(5) is installed near Chitrakoot Government School in the head of the Chitrakoot landslide area. The result shows small displacement with heavy rain in February, March and April. After May, the displacement was slow. In January 2015, over 100mm of compression deformation was recorded. This was caused by human work during the data collection, not by landslide activities. In January 2015, about 20mm of tension deformation was recorded.
EC-1 is installed in the premises of Chitrakoot Government School. It shows 3mm tension displacement immediately after installation in February, however no deformation can be seen after March. In January 2015, about 15mm of tension are recorded.
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Figure 3.4.6 Results of Extensometer (source: JET) a.3 Inclinometer
BH-C2 is installed at the head of Chitrakoot landslide area. Some deviation can be seen below 13m on the inclinometer graph below. This may be caused by axial compressive stress. This axial compressive stress may show vertical stress in the ground. This phenomenon is often seen at the head of landslide where the vertical stress is distinguished as shown in Figure 3.4.9. The graph variations (showing slope angle changes) may be large at the depths where grouting (sand fill) is not perfect. The slip surface of the landslide at BH-C2 may be at about 15m.
BH-C6 is installed near Chitrakoot Government School. The monitoring could be done only 2 times (January and February 2014), since the bend of the pipe at the depth of 6 m is in excess of permissive range for the sensor to pass through. This shows that the landslide with a 7m deep slip surface is very active.
BH-C2 BH-C6
Figure 3.4.7 Results of Inclinometer (source: JET)
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Figure 3.4.8 Vertical Stress at Head of Landslide (source: JET) a.4 Strain gauges
BH-C4 is installed at left of center of Chitrakoot landslide area. Small deformations can be seen at 13m, 21m and above 6m deep. These small deformations may not be caused by landslide movement. It must be continued to be watched carefully.
BH-C5 is installed at the foot of Chitrakoot landslide area. There is nothing worthy of special mention in this monitoring.
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Figure 3.4.9 Results of Strain Gauges (source: JET) a.5 Piezometer
Piezometers were installed at BH-C1 and BH-C3. Piezometer at BH-C3 which is the center of Chitrakoot landslide area was shifted to BPP(11) since over 40 m deep of groundwater level at BH-C3 cannot affect a landslide in Chitrakoot.
BH-C1 is located at the head of Chitrakoot landslide. The groundwater level at BH-C1shows a clear tendency to rise in December or January and to drop in June. This seasonal variation in the groundwater level is 2 month behind the rainy season which is around from November to April. This may be because of slow movement of the groundwater in low permeable ground in the area.
The data lost from August to November in 2013 is due to malfunction of the piezometer controller.
BH-(11) is located near Chitrakoot Government School. The groundwater level data were not obtained from the middle of February 2013 to February 2014 because of malfunction of the piezometer sensor which was soaked in the high level groundwater. In February 2013, the groundwater level at BH-(11) rose above the ground surface. After resumption of the monitoring in February 2014, the groundwater level was almost the same level as the ground surface until June 2014. The groundwater level was dropping gradually after June 2014 until November 2014. The groundwater at BH-(11) would have been under enough pressure to force it to the surface in rainy season, since the groundwater was seen gushing out from the
3-42 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. mouth of the observation hole. The artesian pressure of the groundwater was not able to be confirmed by the piezometer since the water flows out from the mouth of the observation pipe. The groundwater level was probably higher than the ground surface between February to June 2014.
Similarly, there are some other boreholes of which the groundwater level is very high in rainy season in Chitrakoot landslide area.
The groundwater level at BH-C3 was confirmed at about 40m deep in November 2012.
Figure 3.4.10 Results of Piezometer (source: JET)
b. Quatre Soeurs
b.1 Rain gauges
A rain gauge is installed at about 0.5km to the south of Quatre Soeurs landslide.
During the monitoring period (2nd April 2013 to 4th March 2015), much precipitation was recorded in rainy season (November to April). A maximum monthly rainfall of 392.0mm/month in the monitoring period was recorded in January 2015, and the minimum monthly rainfall in the monitoring period was 13.5mm/month recorded in May 2013.
There were seven days when the daily precipitation exceeded 50mm/day in the monitoring period. Daily precipitation exceeding 100mm/day was recorded on only 17th December 2014.
118.5mm of daily precipitation and 58.0mm of hourly precipitation were recorded on 17th December 2014.
98.0mm of daily precipitation was recorded on 21st March 2014, and total continuous precipitation was 117.5mm including the precipitation on 22nd March. It was high intensity rainfall recoding 39.0mm of hourly precipitation.
94.5mm of daily precipitation were recorded on 14th November 2013. It is second heaviest precipitation in the monitoring period. The rainfall was started on 13th November, and total continuous precipitation was 121.5mm. However it was not so high intensity rainfall recoding an hourly precipitation of 19.0mm.
Total yearly precipitation in 2014 was 1541.0mm.
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Figure 3.4.11 Result of Rain Gauge (source: JET)
Table 3.4.3 Monthly Precipitation, The Maximum Daily Precipitation and The Maximum Hourly Precipitation (source: JET) 2013 Month 1 2 3 4 5 6 7 8 9 10 11 12 Monthly - - - 111.0 13.0 38.0 47.5 67.0 25.0 81.5 210.0 92.0 precipitation
Maximum daily - - - 26.0 3.5 10.0 15.5 21.0 10.0 48.5 94.5 53.5 precipitation Maximum hourly - - - 7.5 1.5 5.5 6.0 6.0 6.5 12.0 19.0 23.0 precipitation 2014 Month 1 2 3 4 5 6 7 8 9 10 11 12 Monthly 304.0 118.0 275.0 116.5 72.0 35.0 54.0 43.0 40.0 98.5 42.5 342.5 precipitation
Maximum daily 72.5 21.5 98.0 30.0 17.0 11.0 8.0 8.5 12.0 50.5 16.0 118.5 precipitation Maximum hourly 18.0 4.5 39.0 8.0 9.0 5.0 4.5 4.5 5.0 37.0 10.0 58.0 precipitation
2015 Month 1 2 3 4 5 6 7 8 9 10 11 12 Monthly 392.0 116.0 ------precipitation
Maximum daily 65.0 28.5 ------precipitation Maximum hourly 12.0 7.0 ------precipitation
b.2 Extensometer (laser distance meter)
This extensometer monitoring is manual monitoring measuring distance between two points by a laser distance meter. It was expected that E-Q1 located on the head of the landslide block could be tension and E-Q2 located on the toe of the landslide block could be
3-44 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. compression.
Both E-Q1 and E-Q2 of which variations were within 10mm do not show remarkable movement. E-Q1 shows tendency of tension in winter and compression in summer. E-Q2 shows similar tendencies but behind E-Q1. These tendencies may be due to deformation of the ground or structures by the variation in temperature.
Figure 3.4.12 Result of Laser Distance Meter (source: JET)
b.3 Strain gauges
BH-Q1 is installed in upper landslide block (Block B). There is nothing worthy of special mention on this monitoring.
BH-Q2 is installed in upper landslide block (Block A). Small deformation can be seen at 2m, 7m and 11m deep. These deformations are not big enough to be determined to be due to landslide activities.
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Figure 3.4.13 Results of Strain Gauges (source: JET) b.4 Piezometers
Piezometer at BH-Q2 which is the center of Block A was shifted to BH5 since the groundwater level is almost equal to the sea level following the tide level and over 13 m deep of the groundwater level at BH-Q2 cannot affect the landslide.
8m deep BH5 which was drilled before the project is located beside BH-Q2 (3m away from BH-Q2). The groundwater level follows the amount of the precipitation. In a day with much precipitation, the groundwater level rises to 0.5m below the ground surface. The base level of the groundwater was around 3.5m deep in rainy season, around 4.0m deep in non-rainy season. The groundwater level recorded by the piezometer at BH-Q2 must be shallow groundwater flowing in shallow permeable layer.
Figure 3.4.14 Groundwater at BH-Q2 (source: JET)
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Figure 3.4.15 Results of Piezometer (source: JET) b.5 Groundwater monitoring (manual operation)
The groundwater has been monitored once a month with manually operated water level meters at 6 boreholes including two boreholes of strain gauges, BH-Q1 and BH-Q2.
The results are shown in Figure 3.4.16. Some data are missing because the water levels in the boreholes were lower than the borehole bottoms. The groundwater levels are stable at all boreholes except BH-Q1 and BH-3. The water in the boreholes except BH-Q1 and BH3 may be isolated from the groundwater because strainers in the boreholes might be choked with soil. The water level in the borehole of BH-Q1 which may follows actual groundwater level, rose to about 1m deep in February 2013 from 14m deep in dry season.
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Figure 3.4.16 Water Level in The Boreholes (source: JET)
c. Vallee Pitot
Two wire extensometers are installed at the head of the landslide area (EV1) and at the toe of the landslide area(EV-2).
EV1 which is installed at the head of the landslide area shows 55 mm of tension movement immediately after the installation. After that, some small tension movements are seen with over 10mm continuous precipitation. After January 2014, the variation in displacement became small within 10mm. The large displacement in December 2013 was because an operator who touched the wire of the extensometer. In January 2015, 60mm of big tension deformation was recorded. This deformation showed the landslide activities which affected on the surrounding houses.
EV2 which is installed at the toe of the landslide area shows compression movement immediately after the installation. However, it changes to tension movement in May and the tension movement continues all the time until September. The tension movement may be caused by partial deformation of the canal which EV2 straddles as shown in Figure 3.4.19. Even a big deformation was recorded at EV1 in January 2015, EV2 did not record big deformation.
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Figure 3.4.17 Location of Extensometers (source: JET)
(rain gauge R-C1 is in Chitrakoot) Figure 3.4.18 Results of Extensometer (source: JET)
Figure 3.4.19 Tension Movement at EV2 (source: JET)
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3.5 Geophysical Exploration
3.5.1 Elastic Wave Exploration
a. Purpose of Investigation Elastic wave exploration is generally referred to as seismic exploration. Through generation of elastic wave into the ground and measurement of the propagation velocity at the surface, it helps understand properties of geological layers close to the surface. In the landslide investigation, this method is used to estimate the locations of weathered rock layer and the weathering degree, and to obtain the information about strata sequence and the distribution of fault and fracture zone. The exploration results can also be used as the fundamental information for groundwater draining work design. Generally, the measuring lines for elastic wave exploration are set parallel to the motion direction of the landslide, and the dip direction of the strata. The length of the measuring line should be longer than 6-7 times of the exploration depth, and be controlled in 15 times of the designed exploration depth.
b. Quantity and Specifications Table 3.5.1 shows the specifications of the seismic exploration method and Table 3.5.2 outlines the technical requirements for the survey.
Because the survey area was a residential area, the stacking method by means of hammering was adopted as a survey method. The vibration-receiving point and vibration source point interval were based on the generic value.
The traverse lines in the longitudinal direction of the landslide were designated A-line and those in the transverse direction were designated as B-line and C-line. Due to obstacles and private land along the traverse line, A-line and B-line were subdivided and set. It was possible to set C-line on an almost straight line.
Table 3.5.1 Specifications of the Seismic Exploration (source: JET)
Seismic exploration according to seismic Survey method refraction method (P wave) Specification Stacking method Shaking method Hammering Vibration-receiving point interval 5 m Vibration source point interval About 30 m
Table 3.5.2 Extent & Specifications of the Seismic Exploration (source: JET)
Traverse Traverse line Description Methodology line length (m) 8 consecutive seismic lines of 115m each (lines A1-1 to A1-8) A1-line 920 The seismic profile crosses next to boreholes BH C1&BH C4 2 overlapping seismic lines of 115m each (lines A2-1 & A2-2) A2-line 230 The seismic profile crosses next to borehole BH C5 B1-line 2 consecutive seismic lines of 115m each (lines B1-1 & B1-2) 230 B2A-line 2 overlapping seismic lines of 115m each (lines B2A-1 & B2A-2) 230 B2B-line 1 seismic line of 115m (line B2B) 115 C-line 2 consecutive seismic lines of 115m each (lines C-1 & C-2) 230 Total 1,955
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GEOPHYICAL INVESTIGATION AT CHITRAKOOT LOCATION OF SEISMIC SURVEY LINES
B1
A1 A2 B2A C
B2B
－ SEISMIC SURVEY LINE ○ Geophone
Figure 3.5.1 Location of Seismic Survey Lines at Chitrakoot (source: JET)
c. Exploration Method
c.1 Principles In general, the elastic wave velocity is closely associated with geotechnical conditions such as the following factors:
generation age components degree of alteration cracks moisture content
Its velocity value is high in the well-consolidated base rock, however, even though the degree of consolidation is the same, the more cracks and alterations in the base rock, the slower the elastic wave velocity gets.
Based on the principle of the seismic refraction method, a method of elastic wave exploration, observations were made above the ground of how primary wave (P wave) and secondary wave (S wave) of “elastic undulation” travels through the geological stratum either directly or refracted at different boundaries. By understanding the behavior of the waves, it allows us to determine the subsurface structures. Here, elastic undulation or earthquake motions are generated artificially through hammering, crushing powder, etc.
Figure 3.2.1 shows an example of a seismic waveform observed with 24 geophones. The focus of the earthquake was at 28.7m on the traverse line, and geophones are set at 2.5m
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Figure 3.5.3 is a conceptual diagram of both the seismic wave travel time of each geophone and the seismic wave path passing through the surface layer. The seismic wave arrives earlier in the geophone closer to the focus, and the difference in travel time of the seismic wave depending upon the stratum can be seen.
Figure 3.5.2 The Seismic Wave Figure 3.5.3 Travel Time Curves and Seismic Paths
(source:JET) c.2 Equipment and analysis software specifications
The equipment and analysis software to be used in the seismic exploration are listed below.
Table 3.5.3 List of Equipment to be Used (source: JET)
Name Type Specifications Quantity Maker
DAQ INK High-resolution 24-Bit Seismic Source Digital recorder 1unit System ∆-Σ A/D Converter Company, USA
Integrated GPS receiver Seismic Source Geophone GSR 24 Pieces 2.4GHz Wireless communication Company, USA Analysis software Measurement facility for reflection method DAQ VScope-PC Other Big hammer
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Figure 3.5.4 DAQ LINK ⅡSystem and Measured Image14
c.3 Observation procedure Observation procedure is as follows:
Selecting the Choose position and bearing of traverse line on which exploration is carried traverse line out based on the results of reconnaissance on landslide area
Install the geophones on each survey point while wiring the “takeout cable” from the end of traverse line to connect them with “takeout cable”. Spread work (install the geophones) Install 6 to 7 shot points for each traverse line at predefined points. In the case of hammering, produce vibration by hitting the iron plate placed on the ground with a hammer and the time will be transmitted to the body of Installing the shot recorder from the hammer switch attached to the hammer. points Adjust the noise with amplifier so as to minimize the noise due to the traffic vibration, wind and the like by means of elastic wave survey instrument. Instructions will be given from the measurement headquarter on a timely Measuring basis to produce vibration in each shot point to record its vibration-receiving waveform.
Repeat these tasks (Spread→Producing vibration→Measurement) in sequence as described above to complete the measurement of one spread. Perform the same series of tasks on other traverse lines as well to complete the measuring of all traverse lines.
Extension cable shot mark
Junction line Hammer switch Digital data recorder Hammering Takeout cable Iron plate
Geophone
Figure 3.5.5 Observation Procedure and Diagram of Observation (source: JET)
3-53 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. d. Analysis Method Analysis is conducted with a method using travel-time curve. Arrival time (travel-time) of initial motion of the elastic wave from shot point to each vibration-receiving point (sample rate / sampling interval 500 μs) is read from measurement records in units of 1/1000 seconds to create the travel-time curve.
Shape of travel-time curve reflects the velocity structures, equivalent of velocity distributions of the underground. Gradient of travel-time curve represents the amplitude of apparent elastic wave velocity (the smaller the gradient of curve is, the bigger the velocity value is). The range of same layers that appear on the travel-time velocity varies corresponding to the layer thickness of said velocity layer. This change in the travel-time curve allows the velocity structure to be estimated by means of analysis.
Major analysis methods of travel-time curve include two methods: Hagiwara’s peel off method (Peel off method) most-commonly used in a conventional civil engineering geological survey and a tomographic analysis method (hereinafter referred to as “tomographic method”) developed in recent years. While the peel off method reflects layered subsurface structures well, the tomographic method is suitable for block-like structures (matrix structure) and structures where the velocity varies gradually and the like. Table 3.5.4 shows major differences and characteristics of two analysis methods.
Our analysis used “Hagiwara’s peel off method” to seek the velocity structure.
Table 3.5.4 Comparison between Peel Off and Tomographic Methods (source: JET)
Peel 0ff Method Item Tomographic Method (Hagiwara’s Method) Class of elastic Direct wave + Refracted wave + Direct wave + Refracted wave wave Transparent wave Assuming that the greater the Essentially, same as the “peel off depth is, the bigger the velocity method”. Stereological measurement Structure value becomes. enables the detection of velocity-inversion layer as well. velocity structure Velocity
Constraints of Same velocity in one layer Same velocity in one lattice value Elastic wave propagates at the Elastic wave propagates while How the elastic velocity of lower layer along layer transmitting in each lattice at the unique wave propagates boundary (critical refracted wave) velocity in each lattice. Effects attributable Great to the terrain and Apparent high velocity at convex irregularity at portion Small velocity boundary Apparent low velocity at concave surface portion • Suitable for block-like and pulse-like • Suitable for layer structures structures including eruptive rock and including sedimentary layers. faults in addition to hard-and-soft Features • Suitable for the zoning (large alternate layers. classification) of weathered • Since it is easy to capture slight zones. changes in velocity, detailed interpretation is available.
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e.1 Interpretation
The velocity is read from the data obtained in the measurements, and a travel-time curve is created and analyzed with the peel off method. An elastic wave velocity structure diagram is then created. When the travel-time curve is being made, care must be taken that there is parallelism of the travel-time curve as well as congruity between 2-way velocities and between intercept times. With the peel off method, the elastic wave velocity and velocity boundaries are found based on the travel-time curve.
Below is a typical example (A1-1 Line) of a travel-time curve and velocity structure diagram created according to seismic exploration.
Figure 3.5.6 Travel-time Curve of A1-1 Line (source: JET)
Figure 3.5.7 Analytical Diagram of Velocity Profile of A1-1 Line (source: JET)
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Table 3.5.5 shows the elastic wave velocity obtained from the seismic exploration and its relation to presumed stratum and thickness. In addition, the velocity structure diagrams for each traverse line are shown in Figure 3.5.8～Figure 3.5.13.
The velocity structure is generally categorized into 2～3 strata, and the surface stratum is presumed to be colluvium with an elastic wave velocity of less than about 500m/s. The stratum thickness is less than about 20m and distributed uniformly throughout the entire survey area.
The elastic wave velocity of the base rock shows a value of 1700m/s～3900m/s, more than three times the surface stratum velocity. The variation in velocity in hard base rock composed of basalt is attributed to the prevalence of fractures and cracks inherent in basalt.
The state and hardness of the core of the colluvium and basalt clearly differ, resulting in a difference between the elastic wave velocities for the two.
Table 3.5.5 Summary Table of the Various Strata Identified (source: JET)
Traverse Thickness Seismic velocity line (m) (m/s) -Gravelly silty clay/ colluvium & 310 to 790 Highly to completely weathered basalt/ agglomerate: 3 to 15m A1-line -Moderately to slightly weathered basalt/ agglomerate: from 1742 to 2343 12m deep -Gravelly silty clay/ colluvium:0 to 7m 346 to 463 A2-line -Highly to moderate weathered basalt/ agglomerate: 4 to 12m 878 to 1320 -Slightly weathered basalt/ agglomerate: 7 to 10m 3722 to 3843 -Gravelly silty clay/ colluvium & 442 to 484 B1-line Highly to completely weathered basalt/ agglomerate: 5 to 15m -Slightly weathered basalt/ agglomerate: from 15m deep 2283 to 2285 -Gravelly silty clay/ colluvium: 5 to 8m 389 to 393 B2A-line -Highly to moderate weathered basalt/ agglomerate: 7 to 20m 1033 to 1201 -Slightly weathered basalt/ agglomerate: from 20m deep, 2568 to 3630 -Gravelly silty clay/ colluvium & 472 Highly to completely weathered basalt/ agglomerate: 9 to 19m B2B-line -Moderately to slightly weathered basalt/ agglomerate: from 1998 15m deep -Gravelly silty clay/ colluvium & 443 to 492 Highly to completely weathered basalt/ agglomerate: 4 to 15m C-line -Moderately to slightly weathered basalt/ agglomerate: 10 to 2154 to 2174 15m
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Figure 3.5.8 Seismic Velocity Section (A1-line) (source: JET)
Figure 3.5.9 Seismic Velocity Section (A2-line) (source: JET)
Figure 3.5.10 Seismic Velocity Section (B1-line) (source: JET)
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Figure 3.5.11 Seismic Velocity Section (B2A-line) (source: JET)
Figure 3.5.12 Seismic Velocity Section (B2B-line) (source: JET)
Figure 3.5.13 Seismic Velocity Section (C-line) (source: JET)
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3.5.2 Two-Dimensional Resistivity Exploration
a. Purpose of Investigation In an electrical resistivity, direct current is applied to the ground. Resistivity exploration is to measure generated electrical potential and to estimate the resistivity distribution under the ground. Because the electrical behavior varies by rock composition, type and geological condition, groundwater properties and geological structures can be estimated through the measurement of the electrical resistivity under the ground.
During landslide investigation, based on the two dimensional distribution of the electrical resistivity, the weathered layer, bedrock, permeable layers and their continuity, existing situation of the faults and their continuity under the landslide slope can be estimated. The results can be used as fundamental information for the design of groundwater drainage.
In the two dimensional resistivity exploration, high density electrical potential is measured by placing electrodes at 5m intervals. Then through inverse analysis on a computer using the obtained electrical potential data, resistivity distribution is determined.
b. Quantity and Specifications Figure 3.5.6 outlines the technical requirements for the survey.
The commonly used pole-pole array was adopted as the exploration method. Setting of the traverse lines is basically the same as for the seismic exploration, however the length of the fully extended traverse lines is slightly shorter than that for the seismic exploration.
Table 3.5.6 Specifications of Two-dimensional Resistivity Exploration (source: JET)
Survey method Technical requirements for the survey Electrode interval 5m Maximum depth measured 40m
Table 3.5.7 Extent & Specifications of the Resistivity Exploration (source: JET)
Traverse Traverse line Description Methodology line length (m) Strings of 72 electrodes, spaged5m+6roll-along of 18 electrodes. A1-line Sequence of measurement of 3,598 quadripoles 900 Typical depth of investigation: 40m Strings of 36 electrodes, spaced 5m A2-line Sequence of measurement of 306 quadripoles 175 Typical depth of investigation: 30m Strings of 60 electrodes, spaced 5m B1-line Sequence of measurement of 8,528 quadripoles 295 Typical depth of investigation: 40m Strings of 36 electrodes, spaced 5m B2A-line Sequence of measurement of 306 quadripoles 175 Typical depth of investigation: 35m Strings of 30 electrodes, spaced 5m B2B-line Sequence of measure of 207 quadripoles 145 Typical depth of investigation: 30m Strings of 48 electrodes, spaced 5m C-line Sequence of measurement of 562 quadripoles 235 Typical depth of investigation: 40m Total 1,925
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GEOPHYICAL INVESTIGATION AT CHITRAKOOT LOCATION OF RESISTIVITY SURVEY LINES
B1
A1 A2 B2A C
B2B
－ SEISMIC SURVEY LINE
○ Electrode
Figure 3.5.14 Location of Resistivity Survey Lines in Chitrakoot (source: JET)
c. Exploration Method
c.1 Principles In general, the ground resistivity shows the following trends.
The resistivity value of pelitic rocks is small while the value of coarse-grained aggregates of minerals such as granite is large. The resistivity value of weathered and altered rocks is smaller than that of unweathered rocks with the same geological properties. The resistivity value decreases as water content increases. The resistivity value of fault and crush zone or altered area is smaller than that of their peripheries. The resistivity value of gravel layer is larger than that of clay layer.
Although these trends are commonly observed, the ground resistivity generally depends on many factors such as content of conductive minerals (including clay mineral), porosity, water content and saturation, water quality of pore water (resistivity), and temperature. Furthermore, the resistivity simply indicates lithofacies changes in the same geological layer/rock, degree of weathering/hydrothermal alteration, and water content status in many cases in addition to differences in geological layers and rocks.
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The equipment and analysis software used in two-dimensional resistivity exploration is listed below.
・ SYSCAL R1 PLUS Switch-72 ・ RES2DINV or RESIX-2DI(PC) for pseudo-section inversion to true resistivity (and IP) 2D section ・ Pole bolt（Stainless-round bar） ・ Electrode cable, battery
Figure 3.5.15 Measuring Equipment (SYSCAL R1 PLUS Switch-72) and Pole Bolt15
c.3 Measurement method The method is manual measurement by 2-pole method. Figure 3.5.16 shows a circuit where current I is passed through current electrodes C and C∞ to measure the voltage difference V between P and P∞. The apparent resistivity can be obtained from the following equation using the potential theory of semi-infinite medium.
= 2a V / I (m)
I V
C C∞ P P∞ a
Figure 3.5.16 Electrode Arrays for 2-Pole Method (source: JET) As shown in Figure 3.5.17, the apparent resistivity is measured with an earth resistivity meter from electrodes installed at predetermined intervals of measurement points through non-inductive cables and an electrode scanner.
However, we will manually measure by moving and applying a pair of electrodes C1 and P1 along the survey lines instead of using an electrode scanner.
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PC
C∞ P∞ Electrode scanner Earth resistivity meter
C1 P1
Figure 3.5.17 High-Density Electrical Resistivity Exploration Measuring Method (source: JET)
d. Analysis Method An inverse analysis (inversion) is made using the nonlinear least-squares method to draw a colored sectional view of ground resistivity based on the dataset of measure potential.
Figure 3.5.18 shows a resistivity inversion analysis flow. Procedures for analysis and calculation are as follows.
1) Create an initial model of resistivity distribution using the measured data. 2) Obtain a logical potential based on the resistivity distribution using the finite element method. 3) Calculate the difference (residual) between the measured potential and the logical potential. 4) Calculate the logical potential while modifying the initial model so that the residual becomes minimal. 5) Repeat steps 2) to 4) until the residual converges to gain a final resistivity model.
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Measured data Surveyed data
Edit data Create mesh using finite element method
(1) Create initial model
(2) Calculate logical potential
(3) Calculate residual between (Repeated calculation) measured value and logical value
(4) Residual has Modify model converged? No (Nonlinear least-squares method) Yes
(5) Gain final resistivity model
Plot sectional view
Figure 3.5.18 Resistivity Inversion Analysis Flow (source: JET)
e. Results of Exploration e.1 Interpretation
Using the potential decay curve and others, abnormal data is extracted and excluded from the data obtained from measurements. Dividing the ground into the elements of small domains, a resistivity model is then created. Analysis utilizes the nonlinear least squares method, and the resistivity value of each block is decided upon through inverse analysis that sequentially modifies the resistivity of each block.
Below is an example of analysis model classification (A1-1 Line) by two-dimensional resistivity exploration.
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Figure 3.5.19 Resistivity Sequence of A1-1 Line (source: JET)
e.2 Conclusion
The resistivity values obtained from the two-dimensional resistivity exploration and their relation to the estimated strata and stratum thickness is shown in Table 3.5.8. The resistivity cross sections for each of the traverse lines are shown in Figure 3.5.20～Figure 3.5.24.
The resistivity distribution is generally divided over 2～3 strata, and the surface layer is estimated to be colluvium of less than about 50ohm.m. The stratum thickness is less than about 20m and distributed uniformly over the entire survey area. Also, a fall in resistivity is observed in 3 places on the A1-line, indicating a weathered zone or groundwater flow.
Compared to the resistivity of the surface layer, that of the base rock was high at a value of 50～1000ohm.m or more than 1000ohm.m. The hard rock base is made up of basalt, and the basalt is presumed to have an effect on the resistivity value.
As with the seismic exploration results, there was a clear difference between colluvium and basalt in the results. The fall in resistivity observed on the A1-line should also be verified from observation data such as groundwater levels.
Table 3.5.8 Summary Table of the Various Strata Identified (source: JET)
Traverse Thickness Resistivity line (m) (ohm.m) -Gravelly silty clay/ colluvium & 0 to 50 Highly to completely weathered basalt/ agglomerate: 3 to 15m A1-line -Moderately to slightly weathered basalt/ agglomerate: from 12m 50 to 1000 deep, encountered on a depth of 35m -Gravelly silty clay/ colluvium:0 to 7m with pockets at 15m at the end 0 to 10 of the survey line A2-line -Highly to moderate weathered basalt/ agglomerate: 4 to 12m 10 to 150 -Slightly weathered basalt/ agglomerate: 7 to 10m 150 to 1000 -Fractured basalt: from 22m deep, encountered on a depth of 15m >1000 -Gravelly silty clay/ colluvium & B1-line 0 to 50 Highly to completely weathered basalt/ agglomerate: 5 to 15m
3-64 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. -Slightly weathered basalt/ agglomerate: from 15m deep, 150 to 1000 encountered on a depth of 15m -Gravelly silty clay/ colluvium: 5 to 8m 0 to 10 -Highly to moderate weathered basalt/ agglomerate: 7 to 20m 10 to 50 B2A-line -Slightly weathered basalt/ agglomerate: from 20m deep, 150 to 1000 encountered on a depth of 17m -Gravelly silty clay/ colluvium & 0 to 50 Highly to completely weathered basalt/ agglomerate: 9 to 19m B2B-line -Moderately to slightly weathered basalt/ agglomerate: from 15m 50 to 1000 deep, encountered on a depth of 15m -Gravelly silty clay/ colluvium & 0 to 50 Highly to completely weathered basalt/ agglomerate: 4 to 15m C-line -Moderately to slightly weathered basalt/ agglomerate: 10 to 15m 50 to 1000 -Fractured basalt: from 27m deep, encountered on a depth of 15m to >1000 20m
Figure 3.5.20 Resistivity Pseudosection (A1-line) according to Inverse Analysis (source: JET)
Figure 3.5.21 Resistivity Pseudosection (A2-line) according to Inverse Analysis (source: JET)
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Figure 3.5.22 Resistivity Pseudosection (B1-line) according to Inverse Analysis (source: JET)
Figure 3.5.23 Resistivity Pseudosection (B2A-line) according to Inverse Analysis (source: JET)
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Figure 3.5.24 Resistivity Pseudosection (B2B-line) according to Inverse Analysis(source:JET)
Figure 3.5.25 Resistivity Pseudosection (C-line) according to Inverse Analysis (source: JET)
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3.6 Drilling Survey
3.6.1 Drilling Plan
A drilling survey is conducted by extracting direct core from the ground in order to ascertain the slip plane surface, geological features, and geological structure. For this project all core sampling was conducted with a core diameter of 76～101mm.
a. Field Drilling Schedule
The drilling process in Chitrakoot and Quatre Soeurs is explained below.
a.1 Chitrakoot
The drilling of boreholes BH-C3～BH-C6 commenced at the end of October and was completed in mid-November. Because it took time to verify the landowners, drilling on boreholes BH-C1 and BH-C2 commenced in the beginning of December and was completed in mid-December. The drilling process ended up finishing 2.5 months behind schedule.
The duration of each drilling survey was less than one week.
Table 3.6.1 Field Drilling Schedule (Chitrakoot) (source: JET)
Depth October November December Borehole Installation (m)102030102030102030 BH-C1 48.8612 15 Piezometer BH-C2 50.04 9 Inclinometer BH-C3 50.05 8 - BH-C4 30.030 1 Pipe strain gauge BH-C5 30.023 26 Pipe strain gauge BH-C6 50.012 16 Inclinometer
a.2 Quatre Soeurs
Work commenced in the beginning of October 2012 and was completed mid-October. Drilling took 4 days.
Table 3.6.2 Field Drilling Schedule (Quatre Soeurs) (source: JET)
Depth October November December Borehole Installation (m)102030102030102030 BH-Q1 21.010 13 Pipe strain gauge BH-Q2 21.02 5 Pipe strain gauge
b. Quantity and Location
b.1 Chitrakoot
Details of the drilling survey can be seen in Table 3.6.3. Survey and monitoring locations are
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Table 3.6.3 Borehole Details (source: JET)
Borehole Borehole Depth Borehole Diameter In Situ Test Installation Location (m) (mm) BH-C1 76 48.86 SPT Piezometer
BH-C2 101 50.0 SPT Inclinometer
BH-C3 76 50.0 SPT － Chitrakoot BH-C4 76 30.0 SPT Pipe strain gauge
BH-C5 76 30.0 SPT Pipe strain gauge
BH-C6 101 50.0 SPT Inclinometer
BH-C3 BH-C1
BH-C5 BH-C4 BH-C2
BH-C6
Figure 3.6.1 Survey Locations in Chitrakoot (source: JET)
b.2 Quatre Soeurs
Drilling survey details are listed in Table 3.6.4. Survey and monitoring locations are shown in Figure 3.6.2.
3-69 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. Table 3.6.4 Borehole Details (source: JET)
Borehole Borehole Depth Borehole Diameter In Situ Test Installation Location (m) (mm) BH-Q1 76 21.0 SPT Pipe strain gauge
Quatre Soeurs BH-Q2 76 21.0 SPT Pipe strain gauge
BH-5(existing) 76 NA NA Piezometer
BH-Q1
BH-Q2
Figure 3.6.2 Survey locations in Quatre Soeurs (source:JET)
3.6.2 Core Drilling
a. Specifications
The specifications of the drilling machines and materials are as follows.
Table 3.6.5 Specifications of the Drilling Machines and Materials (source: JET)
Drilling equipment APAFOR38 and APAFOR48 Drilling method Rotary coring-T2-101 Core Barrel NMCL Triple Tube Casing 89mm and 114mm
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Drilling machine Tank/ Tank car
Lorry Material storage
Standard penetration test materials Core tube/ Rod
Photo 3.6.1 The Drilling Machines and Materials (source: JET)
b. Evaluation Standards
The evaluation standards of the drilling core are as follows.
b.1 Degree of weathering
The chart below serves as a guide to the degree of base rock weathering. Using it as a reference, stratum classification was carried out for the borehole log.
3-71 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. Table 3.6.6 Rock Mass Weathering16
Original texture/Grain Descriptive term Fracture condition Surface characteristics condition Fresh Basalt Closed Unchanged Preserved/tight Slightly weathered Discolored and may Partial discoloration/not Preserved/tight Basalt contain thin filling friable Partial to complete Moderately Discolored and may discoloration/not friable Preserved/partial Weathered Basalt contain thin filling except poorly cemented opening samples Discolored and may Mainly Highly weathered contain thin to medium Friable preserved/partial Basalt thick filling opening Partly Completely － Resembles soil Preserved/complete Weathered Basalt separation
b.2 TCR・SCR・RQD
TCR (Total Core Recovery), SCR (Solid Core Recovery), and RQD (Rock Quality Designation) are used as an index to determine the quality of the rock mass. The relation between RQD and degree of base rock quality is as follows.
RQD=（Total length of cores>100mm／Total length of drilling）×100%
Table 3.6.7 Quality Classification of Rocks by RQD Values16
RQD（％） Quality classification of rocks 0 to 25 Very poor 25 to 50 Poor 50 to 75 Fair 75 to 90 Good 90 to 100 Excellent
b.3 Rock Strength・Joint Spacing
The following chart is a guide to the relation between core hardness and core strength.
Table 3.6.8 Strength Description of Rock Material16
Indicative unconfined Term Field description compressive strength (Mpa) Gravel-size lumps can be crushed between finger Very weak <1.25 and thumb. Gravel-size lumps can be broken in half by Weak 1.25 to 5 heavy hand pressure. Only thin slabs, corners or edges can be broken Moderately weak 5 to 12.5 off with heavy hand pressure. When held in the hand, rock can be broken by Moderately strong 12.5 to 50 hammer blows. When resting on a solid surface, rock can be Strong 50 to 100 broken by hammer blows. Very strong Rock chipped by heavy hammer blows. 100 to 200 Extremely strong Rock rings on hammer blows. >200
3-72 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. The following is a reference for classification of joint discontinuity and spacing.
Table 3.6.9 Classification of Discontinuity Spacing17
Description Joint spacing (m) Extremely closely spaced <0.02 Very closely spaced 0.02 to 0.06 Closely spaced 0.06 to 0.2 Moderately spaced 0.2 to 0.6 Widely spaced 0.6 to 2 Very widely spaced 2 to 6 Extremely widely spaced >6
3.6.3 Installation of Observation Equipment
Three types of observation equipment were installed at the boreholes: pipe strain gauges, inclinometers, and water level meters.
a. Installation of Pipe Strain Gauge
The pipe strain gauge was installed according to the following procedures.
・ Excavate a borehole to the specified depth and insert pipe strain gauge while connecting it. At that time, match the alignment mark on the surface of the pipe with the direction of landslide movement, being careful the direction doesn’t shift.
・ Thoroughly embed the pipe strain gauge in the bedrock. The depth is specified as 3～ 5m, but in cases where a base rock slide is conceivable, at least one hole should be excavated and gauge installed more than 10～20m inside the base rock.
・ Strain gauges are generally placed at 1～2m intervals, but if the presence of a slip surface is ascertained with certainty, intervals are less than 1m. Strain gauges in this project were all placed at 1m intervals.
・ The annular space between the borehole walls and the pipes were filled with sand.
・ After pipe strain gauges were embedded, the leads were connected to the data logger.
3-73 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. Table 3.6.10 Specifications of the Pipe Strain Gauge (source: JET)
Materials Type Capability Body of the pipe strain gauge System：two gauges in one direction, Strain gauge system Measurement range：±25,000×10-6 strain Strain limit：1×10-6 strain VP40 Accuracy：0.5% Code edge (length: 20m) Operational temperature：-20°～60°C -6 VP40 Adjustment value：±700×10 Strain (length: 30m) Effective length 1m, filter roll, processed strainer Surplus length of cable 2m, height from the land surface 1m
Installation of the pipe strain gauge Setting of the pipe strain gauge complete
Connection of the data logger Connection of the data logger complete
Setting of the data logger Setting of the protection box
Photo 3.6.2 Installation of the Pipe Strain Gauge (source: JET)
3-74 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. b. Installation of Borehole Inclinometer
The borehole inclinometer was installed according to the following procedures.
・ Excavate a borehole to the specified depth, and verify the depth of the bedrock.
・ Thoroughly embed the guide pipe in the bedrock. The concept is the same as for the pipe strain gauge.
・ One side of the guide pipe’s guide groove is aligned in the anticipated direction of landslide movement, and the guide pipe is hooked up so that the guide grooves connect smoothly.
・ To avoid occurrence of initial deflection, don’t push with excessive force when inserting the guide pipe. Insert the pipe so that it will extend straight and fix the bottom edge of the guide pipe securely to the bedrock. Gradually fill the space around the guide pipe with sand, and install while compacting,
Below is a description of the equipment used and photos of the installation process.
Table 3.6.11 Specifications of the Special Casing Pipe (Guide Pipe) (source: JET)
Materials Type Materials Type
ABS Pipe ABS Pipe Sockets KBF-51-2 KBF-52
ABS Guide Pipe ABS Guide Pipe Socket Length 2m
ABS ABS
KBF-54-1 KBF-54-2
ABS Guide Pipe cap ABS Guide pipe cap Bottom cap Top cap
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Special casing pipe (guide pipe) Insertion of the casing pipe
Positioning of the casing pipe Connection of the casing pipe
Setting of the casing pipe completed Setting of the protection box
Photo 3.6.3 Installation of the Casing Pipe (Guide Pipe) (source: JET)
c. Installation of Water Level Meters
Water level meters were installed according to the following procedures.
・ Excavate a borehole to the specified depth, and verify the depth of the groundwater level.
・ Insert screen-processed PVC pipe, and fill the gap between it and the borehole wall with sand.
・ Taking into consideration the expected margin of fluctuation in the groundwater level, determine the installation depth of the hydraulic water level detector.
・ Raise and lower the fixed depth of the piezometer in the water, checking that the change in water pressure corresponding to the changes in depth is being measured.
3-76 JICA KOKUSAI KOGYO CO., LTD. The Project of Landslide Management NIPPON KOEI CO., LTD. in the Republic of Mauritius (Final Report) CENTRAL CONSULTANT INC. FUTABA INC. Below is a description of the equipment used and photos of the installation process.
Table 3.6.12 Specifications of the Piezometer (source: JET)
Materials Type Capability
Measurement range：0～10m Accuracy of measurement：0.1%FS DS-1 Temperature characteristic：±0.09%FS/10°C (Cable Coverage of temperature：0～30°C length:20m) ： DS-1 Material of body SUS316L Cable Material of cable：Polyurethane (open air length:30m) pipe built in) Material of pressure receiver：Hastelloy Size, Weight：φ25×130mm、about 120g
PVC pipe Installation of PVC pipe completed
Installation of water level meter Setting of the data logger
Photo 3.6.4 Installation of Water Level Meter (source: JET)
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3.6.4 Drilling Results
a. Chitrakoot
Drilling results are summarized in the boring logs and core sample photographs and included in the Supporting Report.
The chart below shows the core recovery, solid core recovery and RQD obtained by means of drilling. The strata can be broadly classified into 3 types.
Table 3.6.13 Standard Penetration Test (source: JET)
Total core Solid core Depth Depth Thickness RQD Borehole Type Recovery Recovery (m) (m) (m) (%) (%) (%) 1 5.00 5.00 100 0 0 BH-C1 48.86 2 10.15 5.15 100 0-50 0-45 3 48.86 38.71 100 45-100 12-100 1 8.00 8.00 100 0 0 BH-C2 50.00 2 9.70 1.70 100 0 0 3 50.00 40.30 100 14-100 0-100 1 6.00 6.00 100 0 0 BH-C3 50.00 2 15.00 9.00 100 0-43 0-30 3 50.00 35.00 100 80-100 65-100 1 7.55 7.55 100 0 0 BH-C4 30.00 2 15.00 7.45 100 0-77 0-77 3 30.00 15.00 100 82-100 60-100 1 5.75 5.75 100 0 0 BH-C5 30.00 2 16.00 10.25 100 0-56 0-35 3 30.00 14.00 100 65-100 60-100 1 7.00 7.00 100 0 0 BH-C 50.00 2 13.00 6.00 100 0 0 3 50.00 37.00 100 10-100 0-100
Table 3.6.14 Relationship between Strata Classification and Geological Features (source: JET)
Type Geology TOP SOIL, COLLUVIUM, ALLUVIUM: Silty-Clay with occasional Cobbles and Boulders 1 Brown to Dark Brown, Dark Grey Soft to Stiff HIGHLY/HIGHLY TO MODERATELY/HIGHLY TO COMPLETELY WEATHERED BASALT/AGGLOMERATE 2 Brown to Light Brown, Grey Weak/Weak to moderate SLIGHTLY WEATHERED BASALT/AGGLOMERATE 3 Grey/Grey to purplish Grey Strong to Very strong
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Drilling results are summarized in the boring logs and core sample photographs and included in the Supporting Report.
The chart below shows the core recovery, solid core recovery and RQD obtained by means of drilling. The strata can be broadly classified into 5 types.
Table 3.6.15 Standard Penetration Test (source: JET)
Total core Solid core Depth Depth Thickness RQD Borehole Type Recovery Recovery (m) (m) (m) (%) (%) (%) 2 2.00 2.00 100 0 0 BH-Q1 21.00 3 7.80 5.80 100 0-33 0-33 5 21.00 13.20 100 44-100 30-100 2 18.75 18.75 100 0 0 BH-Q2 21.00 3 21.00 2.25 100 0-18 0
Table 3.6.16 Relationship between Strata Classification and Geological Features (source: JET)
Type Geology 1 Fill 2 Colluvium 3 HIGHLY WEATHERED BRECCIA/BASALT 4 MODERATELY WEATHERED BRECCIA/BASALT 5 SLIGHTLY WEATHERED BASALT/BRECCIA
3.6.5 Standard Penetration Test
The standard penetration test is conducted to seek the N value in order to determine the hardness, firmness, and soil layer structure of the ground in situ. Test methods are carried out in accordance with BS 1377.
Standards for soil stiffness and consistency are as follows.
Table 3.6.17 Soil Strength Description (source: JET)
Consistency Identification Very soft Easily molded fingers Soft Easily penetrated with thumb Firm Indent by thumb/molded with strong pressure Stiff Indent by thumb Very Stiff Penetrated by thumbnail Hard Penetration by thumbnail difficult
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The results of the standard penetration tests conducted on each borehole are shown in Table 3.6.18.
Most of the geology tested was colluvium. Almost all had a consistency of “very stiff”, and a small portion was “stiff” or “firm”. A great deal of gravel was contained in the colluvium, and there is a possibility that the gravel blows may have caused an exaggerated N value.
The N value of the surface layer of boreholes BH-C3 and BH-C6 is relatively soft at less than 10. The mixture of gravel is irregular, but shows a tendency to become more prevalent in the deeper parts of the colluvium. Based on the soil test results, the matrix of this stratum is mainly composed of fines, and therefore the N value is expected to decline in regard to cohesive soil containing no gravel.
Table 3.6.18 Standard Penetration Test (source: JET)
Depth SPT SPT Estimated UCS,kpa Estimated Borehole Consistency (m) level N value (Jennings and Al,1973) Cu,kpa BH-C1 48.86 3.00 20 150-300 75-150 Very stiff 2.20 33 150-300 75-150 Very stiff 3.35 23 150-300 75-150 Very stiff BH-C2 50.00 6.55 21 150-300 75-150 Very stiff 8.00 19 150-300 75-150 Very stiff 1.00 8 40-80 20-40 Firm 2.55 14 75-150 37-75 Stiff 4.10 16 150-300 75-150 Very stiff BH-C3 50.00 5.45 19 150-300 75-150 Very stiff 8.10 33 150-300 75-150 Very stiff 9.65 41 150-300 75-150 Very stiff 11.51 >51 Possibly cobbles/boulders 2.55 26 150-300 75-150 Very stiff 5.00 10 75-150 37-75 Stiff BH-C4 30.00 6.35 28 150-300 75-150 Very stiff 8.00 36 150-300 75-150 Very stiff 9.35 34 150-300 75-150 Very stiff 1.25 >51 Possibly cobbles/boulders 2.80 31 150-300 75-150 Very stiff BH-C5 30.00 4.25 >51 150-300 75-150 Very stiff Penetration 5.75 Possibly cobbles/boulders not possible 2.00 8 40-80 20-40 Firm 3.85 5 40-80 20-40 Firm 5.30 23 150-300 75-150 Very stiff BH-C6 50.00 7.00 14 75-150 37-75 Stiff 8.80 32 150-300 75-150 Very stiff 10.65 26 150-300 75-150 Very stiff
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The results of the standard penetration tests conducted on each borehole are shown in Table 3.6.19.
The geology tested was colluvium and the consistency was “stiff” or “firm”. Excluding borehole BH-Q1, the N values were almost uniform for the boreholes at a range of 10-20. As in Chitrakoot, the colluvium contained an abundance of gravel, which affected the N value. In addition, because the matrix is composed mainly of fines, the N value is expected to decline in regard to cohesive soil containing no gravel.
Table 3.6.19 Standard Penetration Test (source: JET)
Depth SPT SPT Estimated UCS,kpa Estimated Borehole Consistency (m) level N value (Jennings and Al,1973) Cu,kpa BH-Q1 21.00 1.00 6 40-80 20-40 Firm 1.13 12 75-150 37-75 Stiff 2.20 17 75-150 37-75 Stiff 3.55 15 75-150 37-75 Stiff
BH-Q2 21.00 5.00 15 75-150 37-75 Stiff 6.75 14 75-150 37-75 Stiff 10.35 16 75-150 37-75 Stiff Penetration 13.45 Possibly cobbles/boulders not possible
3-81