Highway Slope Manual

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37 suitable techniques that can allow some of the investigation works to be carried out on or above the slope, e.g. using lightweight platforms and equipment erected from above, so that closure of the road is not required at these locations. Prior to the start of ground investigation works, traffic impact assessments (TIAs) may have to be carried out where road or pedestrian traffic will be affected. Reference should be made to Guidance Note No. RD/GN/021 issued by the <strong>Highway</strong>s Department (1995) on this. Where a TIA is required, adequate time should be allowed for in the ground investigation programme. Depending on the site conditions, it may take 6 to 8 weeks or more to carry out the TIA and obtain the necessary permission to commence the ground investigation works on site. 3.. OTHER CONSIDERATIONS FOR ROAD PROJECTS 3...1 General Ground investigation works such as drillholes for a road project are often carried out concurrently at widely spaced locations. In putting together the investigation requirements, a programme supplemented with a layout plan should be prepared showing the locations and nature of works that are to be carried out concurrently, so that adequate site supervisory personnel can be assigned. This should be done taking into account the actual site conditions ascertained from a walkover survey along the route. At locations where re-routing and/or ducting of any existing services near highway slope features are likely to be required, the locations of the services should be confirmed by inspection pits during ground investigation. Such locations should be surveyed and documented. This information is important to facilitate both design and construction, in particular to minimize the need for re-design during the contract. 3...2 Areas with Signs of Distress or with Known or Suspected Ground Movement/Deformation In situations where new high cuttings are to be excavated in sloping terrain, whether in soil or rock, a central issue is whether the natural ground is inherently stable, or whether it contains relict structures caused by slope movements in the past. Many significant landslides on roads were “second time slides". Therefore, where a proposed route traverses areas with signs of distress, or areas with known or suspected past ground movement/deformation, as identified by aerial photograph interpretation, a detailed study should be carried out to provide data for the assessment of the stability of the terrain and its possible impact on the route. Low altitude aerial photographs and data on past landslides could provide information for assessing whether there has been progressive development of a ground failure involving significant ground deformation (Sun & Campbell, 1999). A site walkover survey should be carried out to collect information on the nature of the distress and/or ground movement/deformation together with geomorphological and engineering geological mapping. Where required, conventional surveying should also be carried out to provide ground
38 movement monitoring and control data at carefully selected locations. In some cases, it may be worthwhile to sink drillholes and install instrumentation such as piezometers and inclinometers to provide subsurface hydrogeological and deformation information to aid interpretation. Where necessary, suitable investigations and tests should be carried out to determine the mass shear strength of the deformed ground for the purpose of slope stability assessment and design. General guidance on slope instability recognition, surface observation, geological mapping, etc., is given in Chapters 8 and 9 of TRB Special Report 247 (Transportation Research Board, 1996). 3...3 Geological Features Adverse to Stability of Cut <strong>Slope</strong>s The presence of adversely oriented clay seams and clay-filled joints in a weathered rock mass (Plates 3.1 and 3.2) can contribute to the failure of highway cut slopes, e.g. the cut slope failure at Fei Tsui Road (GEO, 1996a). Other geological features such as adversely located fault zones or major joint sets, weak or impermeable materials, pre-existing shear surfaces, preferential flow paths and internal erosion pipes, can also affect slope stability. They should be specifically checked for when investigating existing cut slopes, as well as after any new cut faces are formed along the road during construction. Plate 3.1 Fei Tsui Road Landslide Which Plate 3.2 Kaolinite-rich Altered Tuff Exposed at Occurred in August 1995 (GEO, the Fei Tsui Road Landslide 1996a)
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: 36 or features such as dykes or fra
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 49 and 50: 48 Plate 5.1 Surface Runoff Channel
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.
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90 [BLANK PAGE]
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92 [BLANK PAGE]
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94 key natural terrain and man-made
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96 and details of all existing slop
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98 [BLANK PAGE]
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-AA (v) relevant services and utili
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-A2 (m) (n) 1dentify any statutory
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-A4 Notes: (-) An example of a prog
Page 107 and 108:
106 [BLANK PAGE]
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108 Wong, C.K.L. (1998). The New Pr
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110 of slopes and slope owners and
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112 [BLANK PAGE]
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114 (iv)subsidence of ground or roa
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