Highway Slope Manual

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1. INTRODUCTION
1.1 PURPOSE AND SCOPE
The purpose of this Manual is to recommend a standard of good practice on slope
engineering that is specific for the planning, investigation, design and construction of projects
in Hong Kong that involve highway slopes and for their maintenance.
In the context of this Manual, highway (or roadside) slopes are taken to include all
types of man-made slope features (viz. cut slopes, fill slopes and retaining walls) and manmade
features on natural terrain (e.g. boulder fences and check dams), the failure of which
could affect a road. Reference is also made in relevant Sections of the Manual to natural
terrain hazards that could affect a highway where appropriate.
Highway slope owners are taken to mean not only the owners but also the parties who
are responsible for the maintenance of the highway slopes. Road owners are taken to mean
owners of a road. The term “geotechnical engineer” is taken to mean a professionally
qualified person with an adequate level of experience in geotechnical engineering for the
tasks required to be carried out. A suitable qualification is Registered Professional Engineer
(Geotechnical), information on which can be obtained from the Engineers Registration Board
of Hong Kong.
While the guidance given in this Manual is written with public roads in mind, the
principles are also applicable to private roads and railways.
The document is aimed at qualified professional engineers who are conversant with the
relevant engineering principles and tools. It covers general principles and the standard of
care required, but does not contain detailed procedures and methods. It guides the readers to
other published documents including Geotechnical Engineering Office (GEO) publications,
where such details may be found.
Landfill slopes and foundations for embankments on soft ground, which require
special consideration, are not covered in this Manual and readers should refer to relevant
literature on these subjects.
1.2 PROBLEMS WITH HIGHWAY SLOPES IN HONG KONG
The annual total number of reported landslides affecting roads during the period 1984
to 1998 ranges from 33 (in 1984) to 490 (in 1993) with an average of 166. These involved
mainly man-made slope features. Some of these landslides resulted in fatalities, e.g. the
landslides at Kennedy Road (Chan et al, 1996), Castle Peak Road (Chan et al, 1996), Fei Tsui
Road (GEO, 1996a) and Shum Wan Road (GEO, 1996b). Others caused serious disruption
to the traffic and the community, e.g. the rockfall during the Tuen Mun Highway widening
works in 1995 which involved a fatality (Wong, 1997) and the landslide at Ching Cheung
Road in 1997 (Halcrow, 1998). Table 1.1 and Plates 1.1 to 1.3 give examples of highway
slope incidents in recent years which have resulted in fatalities and injuries. Plate 1.4 is an
example of a slope failure which caused the complete closure of a major road for a long
period.
Despite the fact that on average more than 300 natural terrain landslides occur every