Landslide Preventive Works at Po Shan, Mid-Levels - Design and Construction
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Civil Engineering and Development Department Agreement No. CE 28/2004 (GE) Landslide Preventive Works at Po Shan, Mid-levels - Design and Construction Project Profile August 2005 Maunsell Geotechnical Services Ltd ISO 9001 FS 92773 Agreement No. CE28/2004 (GE) Landslide Preventive Works at Po Shan, Mid-levels Design and Construction PROJECT PROFILE August 2005 Agreement No. CE 28/2004 (GE) Landslide Preventive Works at Po Shan, Mid-levels Project Profile TABLE OF CONTENTS 1. BASIC INFORMATION.....................................................................................................................1-1 Project Title......................................................................................................................................1-1 Purpose and Nature of the Project ................................................................................................1-1 Name of Project Proponent............................................................................................................1-1 Location and Scale of Project........................................................................................................1-1 Number and Types of Designated Project Covered by the Project Profile...............................1-2 Name and Telephone Number of Contact Person(s)...................................................................1-2 2. OUTLINE OF PLANNING AND IMPLEMENTATION PROGRAMME.............................................2-1 Implementation and Planning of the Proposed Project ..............................................................2-1 Tentative Project Timetable ...........................................................................................................2-1 Interactions with Other Projects....................................................................................................2-1 3. MAJOR ELEMENTS OF THE SURROUNDING ENVIRONMENT ..................................................3-1 Description of Major Elements of the Surrounding Environment..............................................3-1 Existing and Planned Sensitive Receivers...................................................................................3-4 4. POSSIBLE IMPACT ON THE ENVIORNMENT...............................................................................4-1 Outline of Processes Involved.......................................................................................................4-1 Potential Environmental Impacts ..................................................................................................4-1 5. ENVIRONMENTAL PROTECTION MEASURES TO BE INCORPORATED IN THE DESIGN AND ANY FURTHER ENVIRONMENTAL IMPLICATIONS .....................................................................5-1 Environmental Protection Measures to be incorporated in the Design ....................................5-1 6. USE OF PREVIOUSLY APPROVED EIA REPORTS......................................................................6-1 List of Tables Table 3.1 Representative Noise Sensitive Receivers ..............................................................................3-4 Table 3.2 Representative Air Sensitive Receivers ...................................................................................3-4 Table 3.3a Ecological Value of Secondary Woodland Habitat in the Study Area ......................................3-5 Table 3.3b Ecological Value of Temporary Streams in the Study Area .....................................................3-5 Table 3.3c Ecological Value of Other Habitats in the Study Area..............................................................3-6 Table 4.1 Ranges of Unmitigated Construction Noise Levels..................................................................4-2 Table 4.2 Unmitigated Groundborne Construction Noise Levels at Block A, Po Shan Mansion .............4-3 Table 4.3 Estimated Quantities of Waste Material Arisings .....................................................................4-4 Table 4.4a Overall Impact Evaluation to Secondary Woodland Habitat in the Study Area........................4-5 Table 4.4b Overall Impact Evaluation to Temporary Stream Habitats in the Study Area ..........................4-5 Table 4.4c Overall Impact Evaluation to Other Habitats in the Study Area ...............................................4-6 Table 5.1 Quieter PME Recommended for Adoption during Construction Phase ...................................5-1 Table 5.2 Ranges of Unmitigated and Mitigated Construction Noise Levels ...........................................5-2 D:\PP Final-3.doc i Agreement No. CE 28/2004 (GE) Landslide Preventive Works at Po Shan, Mid-levels Project Profile List of Figures Figure 1.1 Location Plan for the Project Figure 1.2 Proposed Works Layout Plan Figure 1.3 Cross Section of Drainage Adits Figure 1.4 Sub-vertical Drain Typical Details Figure 3.1 Habitat Map Figure 3.2 Locations of Representative Noise Sensitive Receivers Figure 3.3 Locations of Representative Air Sensitive Receivers Figure 3.4 Extent of Works vs. Outline Zoning Plan Figure 4.1 Mitigation to Tunnel Portal Figure 4.2 Rest Garden Reinstatement Design Intent Figure 4.3 Mitigation to Flexible Barrier Figure 5.1 Typical Section of Movable Noise Barrier Appendices Appendix 2.1 Preliminary Construction Programme Appendix 3.1 Representative Photographs of Habitats Recorded in the Study Area Appendix 3.2 Photographic Records of Species of Conservation Importance Appendix 3.3 Plant Species Recorded in the Study Area Appendix 3.4 Fauna Recorded Within the Study Area Appendix 3.5 Landscape and Visual Aspect-Site Photo Appendix 4.1 Proposed Construction Plant Inventory – Unmitigated Appendix 4.1A Construction Plant Inventory for Tunnel Construction Appendix 4.1B Groundborne Construction Noise Assessment Criteria and Methodology Appendix 4.2 Calculation of Construction Noise Levels at Representative Noise Sensitive Receiver – Unmitigated Appendix 4.3 Tree Survey Appendix 5.1A Proposed Construction Plant Inventory – Mitigated (Use of Quieter PME) Appendix 5.1B Proposed Construction Plant Inventory – Mitigated (Use of Quieter PME and Movable Noise Barrier) Appendix 5.2A Calculation of Construction Noise Levels at Representative Noise Sensitive Receiver – Mitigated (Use of Quieter PME) Appendix 5.2B Calculation of Construction Noise Levels at Representative Noise Sensitive Receiver – Mitigated (Use of Quieter PME and Movable Noise Barrier) D:\PP Final-3.doc ii Agreement No. CE 28/2004 (GE) Landslide Preventive Works at Po Shan, Mid-levels Project Profile 1. BASIC INFORMATION Project Title 1.1 The title of this project is known as “Agreement No. CE28/2004 (GE) Landslide Preventive Works at Po Shan, Mid-levels – Design and Construction”. Purpose and Nature of the Project 1.2 The objective of this Project is to carry out detailed design and supervision of landslide preventive works to improve the long-term stability of the Po Shan area against large-scale, deep-seated slope failure and to repair local parts of the hillside to minimize slope deterioration and shallow slope instabilities. 1.3 The Po Shan area is affected by high groundwater level and unfavourable geological conditions. In 1984-85, horizontal drains were installed in part of the area to lower the main groundwater table for improving the stability of the area against large-scale, deep-seated slope failure. However, the available monitoring data show increasing piezometric levels and that some of the horizontal drains, which are 20 years old, are exhibiting a decreasing trend of outflow in recent years. These are indicators of deteriorating drain performance. Therefore, more robust landslide preventive works are proposed to protect the occupants at the Po Shan Area. Name of Project Proponent 1.4 The Project Proponent is the Planning Division of the Geotechnical Engineering Office, Civil Engineering and Development Department, Government of the Hong Kong Special Administrative Region (HKSAR). Location and Scale of Project 1.5 The proposed landslide preventive works would be constructed to protect the existing residential developments at the toe of the project site. The location of the project is shown in Figure 1.1. Figure 1.2 shows the general layout of the Project. 1.6 The major items of works are summarized as follows: Underground Drainage Adits • Two underground drainage adits, comprising the following elements (Figure 1.2 refers), would be constructed to lower the main groundwater table - A m 7.7m (H) x 10m (W) tunnel portal would be constructed at the park adjacent to Po Shan Mansion - A 6.5m (H) x 8m (W) x 30m (L) portal chamber would be constructed for connection of the two proposed drainage adits (Tunnel No. 1 and No. 2) - 2 nos. of 3.5m diameter underground drainage adits, Tunnel No. 1 and No. 2, with length 260m and 175m respectively, would be constructed at the upper and lower portion of the Po Shan Area • About 100 nos. of sub-vertical drains with various lengths from 30m to 80m would be installed upwards from the drainage adits to a minimum length of 2m into completely decomposed volcanic rock. The drains will consist of an outer, 114mm outside diameter perforated casing; and a geotextile-wrap protected, 50mm outside diameter, slotted well-screen inner tube. (Figure 1.3 refers) D:\PP Final-3.doc 1-1 Agreement No. CE 28/2004 (GE) Landslide Preventive Works at Po Shan, Mid-levels Project Profile Flexible Barriers • A 4m high, approximately 100m long flexible barrier would be installed along the lower