6. OTHER CONSIDERATIONS
6.7 CONSTRUCTION REVIEW
6.4 BUILDABILITY
In prescribing improvement works to slope features using prescriptive measures, due consideration should be given to assessing the buildability of the works with respect to the site conditions. In particular, designers should give due consideration to the buildability of soil nails in ensuring that the design is practical and buildable (GEO, 2008).
6.5 WORKS IN THE VICINITY OF SENSITIVE STRUCTURES
When carrying out improvement works to slope features in the vicinity of sensitive structures, such as old buildings with shallow foundations, buildings that have previously been subjected to disturbance and important underground service utilities that are vulnerable to ground movement, designers should ensure that the proposed prescriptive measures will not induce undue disturbance or excessive ground movement to the sensitive structures.
Where deemed necessary, suitable preventive or mitigation measures should be implemented to minimise the potential disturbance that could be caused by the prescriptive measures. The need for condition or defects survey of the sensitive structures and setting up of an appropriate monitoring system should also be considered.
6.6 CONSTRUCTION SUPERVISION AND CONTROL
The necessary construction control for prescriptive measures is similar to that for any other form of slope works which are designed analytically. Adequate site supervision and control should be provided during the implementation of the measures. General guidance on aspects of construction control is given in Chapter 9 of the Geotechnical Manual for Slopes (GCO, 1984). Chapter 6.2 of Geoguide 7 : Guide to Soil Nail Design and Construction (GEO, 2008) also provides guidance on construction supervision and control of soil nailing works.
6.7 CONSTRUCTION REVIEW
The application of prescriptive measures does not involve detailed ground investigation and design analyses at the design stage. It is therefore of paramount importance that construction reviews are carried out during various stages of construction to examine the actual condition of the slope feature and verify the validity of the design assumptions.
Construction reviews should include site inspections and assessment of the geology, slope-forming materials and groundwater conditions, together with verification of whether the qualifying criteria for application of the prescriptive measures have been met. The reviews should also include an evaluation of the suitability and adequacy of the specified types and items of prescriptive measures, as well as recommendations on the necessary design modifications to cater for the actual site and ground conditions as revealed.
Every opportunity should be taken in inspecting any exposed slope-forming materials for adverse geological or groundwater conditions, and identifying any significant differences
between the actual conditions and that assumed during the design stage. This can be done most effectively at the time when the prevailing slope surface cover has been removed, during excavation for subsurface drainage works, and during drilling for raking drains or soil nails.
Where deemed necessary, geological advice may be sought from an experienced engineering geologist on the presence of any adverse geological conditions. The importance of engineering geological input during construction is emphasised in GEO Publication No. 1/2007 : Engineering Geological Practice in Hong Kong (GEO, 2007d).
The findings and recommendations of construction reviews, including sketches, drawings, notes and photographs which record the site observations and design amendments, should be properly documented as ‘Site Inspection Records’ in the “Record Sheets for Prescriptive Measures on Man-made Slope Features” (Figure 2.2). The record sheets, together with other information as specified in Geoguide 5 : Guide to Slope Maintenance (GEO, 2003), should be included in the Maintenance Manual.
6.8 MAINTENANCE
Regular and proper maintenance should be provided to slope features with prescriptive measures. General guidance on recommended good practice for maintenance works for slope features, including the provision of safe access, is given in Geoguide 5 (GEO, 2003).
Raking drains used as prescriptive measures should not be considered as “Special Measures” as defined in Geoguide 5, and the monitoring requirements stipulated in Section 5 of Geoguide 5 are not applicable to these drains. Regular inspections and routine maintenance of the raking drains should however be carried out.
Where water-carrying services are present which are judged to have a destabilising effect on a slope feature in the event of leakage, the guidance given in Geoguide 5 should be followed.
REFERENCES
Au, S.W.C. & Suen, R.Y.C. (1991a). The Role of Environmental Factors in Triggering Failures (Special Project Report No. SPR 3/91). Geotechnical Engineering Office, Civil Engineering Department, Hong Kong, 103 p.
Au, S.W.C. & Suen, R.Y.C. (1991b). The effect of road drainage and geometry in causing roadside slope failures. Proceedings of the Ninth Asian Regional Conference on Soil Mechanics and Foundation Engineering, Bangkok, vol. 1, pp. 373-376.
Brand, E.W., Hencher, S.R. & Youdan, D.G. (1983). Rock slope engineering in Hong Kong.
Proceedings of the Fifth International Rock Mechanics Congress, Melbourne, vol. 1, pp. C17-C24. (Discussion, vol. 3, G126).
BSI (2004). Eurocode 7. Geotechnical Design. General Rules (BS EN 1997-1 : 2004).
British Standard Institution, London, 172 p.
CEDD (2006). General Specification for Civil Engineering Works. Civil Engineering and Development Department, Hong Kong.
Dubin, B.I., Watkins, A.T. & Chang, D.C.H. (1986). Stabilisation of existing rock faces in urban areas of Hong Kong. Proceedings of the Conference on Rock Engineering and Excavation in an Urban Environment, Hong Kong, pp. 155-171.
ETWB (2006a). Code of Practice on Monitoring and Maintenance of Water-carrying Services Affecting Slopes. Environment, Transport and Works Bureau, Government Secretariat, Hong Kong, 93 p.
ETWB (2006b). Tree Preservation (Environment, Transport and Works Bureau Technical Circular (Works) No. 3/2006). Environment, Transport and Works Bureau, Government Secretariat, Hong Kong, 14 p.
Furgo Scott Wilson Joint Venture (2008). Review of Sub-surface Drainage Provisions for Recompacted Fill Slopes (GEO Report No. 225). Geotechnical Engineering Office, Civil Engineering and Development Department, Hong Kong, 69 p.
GCO (1984). Geotechnical Manual for Slopes. (2nd Edition). Geotechnical Control Office, Civil Engineering Services Department, Hong Kong, 295 p.
GCO (1987). Guide to Site Investigation (Geoguide 2). Geotechnical Control Office, Civil Engineering Services Department, Hong Kong, 359 p.
GCO (1988). Guide to Rock and Soil Descriptions (Geoguide 3). Geotechnical Control Office, Civil Engineering Department, Hong Kong, 189 p.
GEO (1993). Guide to Retaining Wall Design (Geoguide 1). (2nd Edition). Geotechnical Engineering Office, Civil Engineering Department, Hong Kong, 258 p.
GEO (2000a). Technical Guidelines on Landscape Treatment and Bio-engineering for Man-made Slopes and Retaining Walls (GEO Publication No. 1/2000). Geotechnical Engineering Office, Civil Engineering Department, Hong Kong, 146 p.
GEO (2000b). Highway Slope Manual. Geotechnical Engineering Office, Civil Engineering Department, Hong Kong, 114 p.
GEO (2003). Guide to Slope Maintenance (Geoguide 5). (3rd Edition). Geotechnical Engineering Office, Civil Engineering Department, Hong Kong, 132 p.
GEO (2004). Guidelines for Assessment of Old Masonry Retaining Walls in Geotechnical Studies and for Action to be Taken on Private Walls (GEO Circular No. 33).
Geotechnical Engineering Office, Civil Engineering and Development Department, Hong Kong, 16 p.
GEO (2006). Hydraulic Design of Stepped Channels on Slopes (GEO Technical Guidance Note No. 27). Geotechnical Engineering Office, Civil Engineering and Development Department, Hong Kong, 16 p.
GEO (2007a). Fill Slope Recompaction – Investigation, Design and Construction Considerations (GEO Technical Guidance Note No. 7). Geotechnical Engineering Office, Civil Engineering and Development Department, Hong Kong, 6 p.
GEO (2007b). Guidelines for Classification of Consequence-to-Life Category for Slope Features (GEO Technical Guidance Note No. 15). Geotechnical Engineering Office, Civil Engineering and Development Department, Hong Kong, 14 p.
GEO (2007c). Update of GEO Publication No. 1/2000 - Technical Guidelines on Landscape Treatment and Bio-engineering for Man-made Slopes and Retaining Walls (GEO Technical Guidance Note No. 20). Geotechnical Engineering Office, Civil Engineering and Development Department, Hong Kong, 8 p.
GEO (2007d). Engineering Geological Practice in Hong Kong (GEO Publication No. 1/2007). Geotechnical Engineering Office, Civil Engineering and Development Department, Hong Kong, 278 p.
GEO (2008). Guide to Soil Nail Design and Construction (Geoguide 7). Geotechnical Engineering Office, Civil Engineering and Development Department, Hong Kong, 97 p.
Hencher, S.R. (1985). Limitations of stereo-graphic projections for rock slope stability analysis. Hong Kong Engineer, vol. 13, No. 7, pp. 37-41.
Ho, K.K.S., Sun, H.W. & Hui, T.H.H. (2003). Enhancing the Reliability and Robustness of Engineered Slopes (GEO Report No. 139). Geotechnical Engineering Office, Civil Engineering Department, Hong Kong, 63 p.
Hoek, E. & Bray, J. (1981). Rock Slope Engineering (Revised 3rd Edition). Institution of Mining and Metallurgy, London, 358 p.
Hong Kong Government (1991). Tree Planting and Maintenance in Hong Kong. Hong
Kong Government, 53 p.
Hui, T.H.H., Sun, H.W. & Ho, K.K.S. (2007). Review of Slope Surface Drainage with Reference to Landslide Studies and Current Practice (GEO Report No. 210).
Geotechnical Engineering Office, Civil Engineering and Development Department, Hong Kong, 61 p.
Knill, J.L., Lumb, P., Mackey, S., de Mello, V.F.B., Morgenstern, N.R. & Richards, B.G.
(1999). Report of the Independent Review Panel on Fill Slopes (report reprinted as GEO Report No. 86). Geotechnical Engineering Office, Civil Engineering Department, Hong Kong, 36 p.
Lam, T.S.K., Sivaloganathan, K. & So, C.W. (1989). Monitoring and Maintenance of Horizontal Drains (Technical Note No. TN 2/89). Geotechnical Control Office, Civil Engineering Department, Hong Kong, 24 p.
Lui, B.L.S. & Shiu, Y.K. (2005). Prescriptive Soil Nail Design for Concrete and Masonry Retaining Walls (GEO Report No. 165). Geotechnical Engineering Office, Civil Engineering and Development Department, Hong Kong, 76 p.
Malone, A.W. (1985). Reliability of the Design of Cuttings in Hong Kong (Discussion Note No. DN 3/85). Geotechnical Control Office, Civil Engineering Department, Hong Kong, 20 p.
Martin, R.P., Siu, K.L. & Premchitt, J. (1995). Performance of Horizontal Drains in Hong Kong (GEO Report No. 42). Geotechnical Engineering Office, Civil Engineering Department, Hong Kong, 109 p.
Muhunthan, B., Shu, S., Sasiharan, N., Hattamleh, O.A., Badger, T.C., Lowell, S.M. &
Duffy, J.D. (2005). Design Guidelines for Wire Mesh/Cable Net Slope Protection.
Washington State Transportation Centre, Washington, 60 p.
Pun, W.K. & Li, A.C.O. (1993). Report on the Investigation of the 16 June 1993 Landslip at Cheung Shan Estate, Kwai Chung (Advisory Report No. ADR 10/93). Geotechnical Engineering Office, Civil Engineering Department, Hong Kong, 14 p.
Pun, W.K., Pang, P.L.R. & Li, K.S. (2000). Recent developments in prescriptive measures for slope improvement works. Proceedings of the Symposium on Slope Hazards and their Prevention, Jockey Club Research and Information Centre for Landslip Prevention and Land Development, Hong Kong, pp. 303-308.
Pun, W.K. & Urciuoli, G. (2008). Soil nailing and subsurface drainage for slope stabilisation.
Proceedings of the Tenth International Symposium on Landslides and Engineered Slopes, Xian, vol. 1, pp. 85-126.
Shiu, Y.K. & Chang, G.W.K. (2005). Soil Nail Head Review (GEO Report No. 175).
Geotechnical Engineering Office, Civil Engineering and Development Department, Hong Kong, 106 p.
Sun, H.W. & Lam, T.T.M. (2006). Use of Standardised Debris-resisting Barriers for Mitigation of Natural Terrain Landslide Hazards (GEO Report No. 182).
Geotechnical Engineering Office, Civil Engineering and Development Department, Hong Kong, 92 p.
Wong, A.C.W. & Pun, W.K. (1999). Prescriptive Design of Skin Walls for Upgrading Old Masonry Retaining Walls (Special Project Report No. SPR 3/99). Geotechnical Engineering Office, Civil Engineering Department, Hong Kong, 36 p.
Wong, H.N. & Ho, K.K.S. (1995). General Report on Landslips on 5 November 1993 at Man-made Features in Lantau (GEO Report No. 44). Geotechnical Engineering Office, Civil Engineering Department, Hong Kong, 78 p. plus 1 drawing.
Wong, H.N. & Pang, L.S. (1996). Application of Prescriptive Measures to Soil Cut Slopes (GEO Report No. 56). Geotechnical Engineering Office, Civil Engineering Department, Hong Kong, 52 p.
Wong, H.N., Pang, L.S., Wong, A.C.W., Pun, W.K. & Yu, Y.F. (1999). Application of
Prescriptive Measures to Slopes and Retaining Walls (GEO Report No. 56).
(2nd Edition). Geotechnical Engineering Office, Civil Engineering Department, Hong Kong, 73 p.
Works Bureau (1993). Control of Visual Impact of Slopes (Works Bureau Technical Circular No. 25/1993). Works Bureau, Government Secretariat, Hong Kong, 4 p.
Works Bureau (1999). Geotechnical Manual for Slopes - Guidance on Interpretation and Updating (Works Bureau Technical Circular No. 13/99). Works Bureau, Government Secretariat, Hong Kong, 12 p.
Works Bureau (2000). Improvement to the Appearance of Slopes (Works Bureau Technical Circular No. 17/2000). Works Bureau, Government Secretariat, Hong Kong, 3 p.
Yu, Y.F., Siu, C.K. & Pun, W.K. (2005). Guidelines on the Use of Prescriptive Measures for Rock Cut Slopes (GEO Report No. 161). Geotechnical Engineering Office, Civil Engineering and Development Department, Hong Kong, 31 p.