Republic of Mauritius Landslide Management Unit: LMU, Ministry of Public Infrastructure and Land Transport: MPI TECHNICAL COOPERATION PROJECT : LANDSLIDE ADVISER FOR MAURITIUS MANUAL February 2018 Japan International Cooperation Agency (JICA) Kokusai Kogyo Co., Ltd. GE JR 18-025 CONTENTS 1. Manual for Survey and Countermeasures of Slope Failure Rock fall and Debris Flow 2. Procedure Manual for Landslide 3. Technical Guideline for Initial Survey 㻸㼛㼏㼍㼠㼕㼛㼚㻌㼛㼒㻌㻿㼠㼡㼐㼥㻌㻭㼞㼑㼍 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 㻰㼑㼠㼍㼕㼘㻌㻹㼍㼜 Rate of Currency Translation 1 USD = 32.1306 MUR = 110.69 JPY 100 MUR = 2.95035 USD = 326.57 JPY MUR: Mauritius Rupee As of 17 January 2018 JAPAN INTERNATIONAL COOPERATION AGENCY (JICA) MINISTRY OF PUBLIC INFRASTRUCTURE AND LAND TRANSPORT (MPI) Manual for Survey and Countermeasure of Slope Failure, Rock Fall and Debris Flow September 2017 Landslide Management Unit, Ministry of Public Infrastructure and Land Transport and KOKUSAI KOGYO CO., LTD. Preface Japan International Cooperation Agency (hereinafter JICA) has implemented the ‘Project of landslide management in Mauritius’ (hereinafter the Previous Project) from April 2012 to March 2015 as a part of the climatic change adaptation and disaster mitigation program for Small Island Developing States (SIDS). “Technical guideline for initial survey” and “Procedure manual for landslide” were prepared during the Previous Project in 2015. Technical Cooperation Project: Landslide Advisor for Mauritius (hereinafter the Following Project) is planned to be implemented as a successor of the Previous Project. The Following Project is focused on the phenomena of slope failures, Rock Falls and debris flows, which were not dealt as main phenomena in the Previous Project. Furthermore, the technical transfer planned in the Following Project has to be implemented by sharing information and cooperating with the ongoing and planned projects by other donors to suit the development capacity of the administration of Mauritius. One of the products of the Following Project is the manual for slope failures, Rock Falls and debris flows. This manual is based on the experience and knowledge gained from the activities carried out by JICA Expert Team (JET) in the Following Project, and technical guidelines and manuals of the Ministry of Land, Infrastructure, Transport and Tourism, Japan (MLIT), mainly by Public Works Research Institute in Japan (PWRI). This manual is a technical guidance for preliminary survey, design of the structural countermeasures, execution, work management and inspection, and maintenance of the structures. By using this manual, basic knowledge and procedure of survey and countermeasure can be obtained. Depending on the limitations of the site condition, period and budget of investigation and construction, etc., methods and type of countermeasures might vary to suit each site. It is expected that the engineers of MPI and District Councils will carry out survey and countermeasure planning for slope failures, Rock Falls and debris flows through their experience and ideas in Mauritius and revise this manual. JICA Expert Team (JET) Chief Advisor: Kensuke Ichikawa, Kokusai Kogyo Co., Ltd. This manual was prepared by JICA Expert Team based on the “Manual for Highway Earthworks in Japan, January 2004”, by Public Works Research Institute in Japan (PWRI). Some information and examples were included from the experience of the Projects in Mauritius on slope countermeasures. The JICA Expert Team expresses their appreciation to PWRI Japan for the permission of usage. Permission No. 㸦ᅜ◊㸧ᅵ◊ᴗ➨ྕ㸦ᖹᡂᖺ᭶᪥㸧 Contents page 1 Introduction ........................................................................................... 1 1.1 What is a Landslide?............................................................................................. 1 1.1.1 Definition of Landslide .............................................................................................. 1 1.1.2 Type of slope disasters in Mauritius .......................................................................... 3 1.1.3 Location map and inventory ...................................................................................... 6 1.2 Procedure Manual of Slope Failures, Rock Falls and Debris Flows .................... 9 1.2.1 Basic Procedures and Contents .................................................................................. 9 1.2.2 Proceedings of Slope Earthworks ............................................................................ 11 1.3 Explanation of Technical Terms......................................................................... 16 2 Surveys ................................................................................................ 18 2.1 Introduction ........................................................................................................ 18 2.1.1 Relationship between Procedure of Slope Earthwork and Soil Investigation ......... 18 2.1.2 Survey Method ........................................................................................................ 18 2.2 Survey on Slope Failures .................................................................................... 19 2.2.1 Checkpoints of Survey............................................................................................. 19 2.2.2 Cut Slope and Natural Slope Failures ...................................................................... 19 2.2.3 Survey on Cut Slope Stability ................................................................................. 20 2.2.4 Survey on Slope Failures Requiring Extra Precautions ........................................... 22 2.2.5 Surveys for Planting ................................................................................................ 24 2.3 Survey on Rock Fall ........................................................................................... 25 2.3.1 Checkpoints of Survey............................................................................................. 25 2.3.2 Survey on Rock Fall Requiring Extra Precautions .................................................. 27 2.4 Survey on Debris Flow ....................................................................................... 28 2.4.1 Checkpoints of Survey............................................................................................. 28 2.4.2 Survey on Occurrence of Debris Flow .................................................................... 30 2.4.3 Survey on Estimation of Scale, Character and Inundation Area of Debris Flow .... 30 2.5 Slope Disaster Related Structures (Drainage, Retaining Wall and Culvert) ...... 31 2.5.1 Survey on Drainage Systems ................................................................................... 31 2.5.2 Survey on Retaining Wall and Culvert .................................................................... 33 3 Design .................................................................................................. 36 3.1 Introduction ........................................................................................................ 36 3.1.1 Basic Principles ....................................................................................................... 36 3.1.2 Important Points for Design .................................................................................... 37 3.2 Cut Slopes ........................................................................................................... 38 3.2.1 Standard Cross-Section of Cut Slopes ..................................................................... 38 3.2.2 Cuts Requiring Extra Precautions ............................................................................ 42 3.3 Slope Protection .................................................................................................. 45 3.3.1 Selection of Slope Protection Works ....................................................................... 45 3.3.2 Important Points for Introduction of Slope Protection Works ................................. 53 3.3.3 Planting .................................................................................................................... 54 3.3.4 Slope Protection Works with Structures .................................................................. 59 3.4 Countermeasures for Rock Fall .......................................................................... 72 3.4.1 Selection of Countermeasures for Rock Fall ........................................................... 72 3.4.2 Important Points for Application of Countermeasures for Rock Fall ...................... 75 3.5 Countermeasures for Debris Flow ...................................................................... 83 3.5.1 Selection of Countermeasures for Debris Flow ....................................................... 83 3.5.2 Important Points for Countermeasures for Debris Flow .......................................... 85 3.6 Slope Disaster Related Structures (Drainage, Retaining Wall and Culvert) ...... 88 3.6.1 Drainage .................................................................................................................. 88 3.6.2 Retaining Wall ....................................................................................................... 106 3.6.3