Highway Slope Manual

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47 5. DRAINAGE AND WATER-CARRYING SERVICES 5.1 GENERAL Slope drainage, road drainage and water-carrying services should be engineered in an integrated manner to ensure that water is channelled safely without impairing ground stability 勾 General guidance on the provision of subsurface drainage measures and design of slope surface drainage is given in Chapters 4 and 8 respectively of the Geotechnical Manual for Slopes (GCO, 1984) 勾 Guidance on prescriptive surface and subsurface drainage measures applicable to existing slopes is given in GEO Report No 勾 56 (Wong et al, 1999) 勾 Methods for the design of road drainage and road pavement subsoil drainage are covered in Road Note 6 “Road Pavement Drainage" (Highways Department, 1994) and Road Note 8 “Subsoil Drainage for Road Pavement" (Highways Department, 2000) respectively 勾 Guidance on the planning, design and management of stormwater drainage systems and facilities is given in the Stormwater Drainage Manual (Drainage Services Department, 2000) 勾 Leakage of water from buried water-carrying services (including sewers, stormwater drains and watermains) can trigger large-scale landslides 勾 The fatal landslide which occurred in 1994 at Kwun Lung Lau (GEO, 1994) is a well documented example 勾 Reference should be made to Section 9 勾 7 of the Geotechnical Manual for Slope (GCO, 1984), Section 6 勾 2 勾 4 of Chapter 7 of the Hong Kong Planning Standards and Guidelines (Planning Department, 1994) and the Code of Practice on Inspection & Maintenance of Water Carrying Services Affecting Slopes (Works Branch, 1996) for guidance on the standards of good practice to prevent leakage from water-carrying services affecting the stability of slopes 勾 5.2 SLOPE DRAINAGE AND ASSOCIATED ROAD DRAINAGE 5.2.1 General Considerations Unless the highway slope drainage and associated road drainage systems are properly designed and maintained, surface runoff will overflow onto and channelise along roads 勾 If this surface runoff is not drained in time, water may overflow onto the downhill area and trigger serious landslides (Plates 5 勾 1 and 5 勾 2) 勾 Landslides can occur at a road section where: (a) the upslope drainage or the associated road drainage is partially or fully blocked or has an inadequate design capacity; during rainstorms, the road section will collect a large volume of surface runoff from uphill areas, which may discharge onto the downhill slope, and (b) the slope below the road onto which the surface water may overflow is a substandard man-made feature, or steep natural terrain of marginal stability, or ground susceptible to erosion or washout by concentrated surface water flow 勾
48 Plate 5.1 Surface Runoff Channelising along a Road Plate 5.2 Shum Wan Road Landslide in August 1995 (GEO, 1996b) Table 5 勾 1 gives examples of locations which satisfy criteria (a) and (b) above 勾 If the failure of the ground at these locations involves slopes in the Consequence-to-life Category 1 or Economic Consequence Category A (see Section 4 勾 2), then the road section is a ‘critical' location in terms of impact of drainage on slope stability 勾
Page 1 and 2: HIGHWAY SLOPE MANUAL GEOTECHNICAL E
Page 3 and 4: 2 。 The Government of the Hong Ko
Page 5 and 6: 4 STEERING COMMITTEE: Geotechnical
Page 7 and 8: 6 Page No. 3. SITE INVESTIGATION 33
Page 9 and 10: 8 Page No. APPENDICES APPENDIX A -
Page 11 and 12: 10 LIST OF FIGURES Figure No. Page
Page 13 and 14: 12 LIST OF LATES Plate No. Page No.
Page 15 and 16: 14 [BLANK PAGE]
Page 17 and 18: 16 year (Evans et al, 1998), they h
Page 19 and 20: 18 Plate 1.4 Landslide at Ching Che
Page 21 and 22: 20 Plate 1.8 Steep Natural Terrain
Page 25 and 26: 24 Notes: (1) The projects in the P
Page 27 and 28: 26 of the geotechnical hazards and
Page 29 and 30: 28 Table 2.2 Geotechnical Haards Th
Page 31 and 32: 30 for carrying out a GA is given i
Page 35 and 36: 34 Table 3.1 Potential Uses of Diff
Page 37 and 38: 36 or features such as dykes or fra
Page 39 and 40: 38 movement monitoring and control
Page 41 and 42: 40 landslide debris, and the nature
Page 43 and 44: 42 Notes: (1) This Figure is based
Page 45 and 46: 44 Table 4.5 Recommended Minimum Fa
Page 47: 46 [BLANK PAGE]
Page 51 and 52: 50 Cascades, with cover where neces
Page 53 and 54: 52 (a) Trash Grill at Inlet of Cros
Page 55 and 56: 54 5.2.3 Drainage Improvement Works
Page 57 and 58: 56 For the control of visual impact
Page 59 and 60: 58 Plate 6.3 Pattern and Texture Pl
Page 61 and 62: 60 ighways are environments with a
Page 63 and 64: 62 Filling operations for a highway
Page 65 and 66: 64 Blasting is the most common meth
Page 67 and 68: 66 Notes: (1) The responsibility fo
Page 69 and 70: 68 Results of Rockfall Protective B
Page 73 and 74: 72 overseeing the maintenance of th
Page 75 and 76: 74 In addition to the slope upgradi
Page 77 and 78: 76 after each heavy rainstorm event
Page 79 and 80: 78 d n n d d d d d d d
Page 81 and 82: 80 event of a landslide should be b
Page 85 and 86: 84 Federal Highway Administration (
Page 87 and 88: 86 Highways Department (1996). Mana
Page 89 and 90: 88 Wong, H.N., Pang, L.S., Wong, A.
Page 95 and 96: 94 key natural terrain and man-made
Page 97 and 98: 96 and details of all existing slop
Page 99 and 100:
98 [BLANK PAGE]
Page 101 and 102:
-AA (v) relevant services and utili
Page 103 and 104:
-A2 (m) (n) 1dentify any statutory
Page 105 and 106:
-A4 Notes: (-) An example of a prog
Page 107 and 108:
106 [BLANK PAGE]
Page 109 and 110:
108 Wong, C.K.L. (1998). The New Pr
Page 111 and 112:
110 of slopes and slope owners and
Page 113 and 114:
112 [BLANK PAGE]
Page 115:
114 (iv)subsidence of ground or roa
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