Highway Slope Manual

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landslide debris, and the nature of the highway. Examples of consequence­to­life categories
and economic consequence categories of highway slopes directly affecting a road are given in
Tables 4.2 and 4.3 respectively.
Table 4.2 Consequence-to-life Categories of Highway Slopes
Examples
Slopes affecting roads with very heavy vehicular traffic density
Slopes affecting roads with moderate to heavy vehicular traffic density
Consequence-to-life Category
1 2 3
Slopes affecting roads with very low to low vehicular traffic density 9
Notes: (1) The above examples are for guidance only.
(2) Reference may be made to the nomograph in Figure 4.1.
(3) Where a highway slope also affects other facilities (e.g. buildings), the highest consequence category
should be adopted for the slope.
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Table 4.3 Economic Consequence Categories of Highway Slopes
Economic Consequence Category
Examples
A B C
Slopes affecting expressways, urban or rural trunk roads, primary
distributors or roads of strategic importance (e.g. North Lantau
Expressway, Tuen Mun Highway, Ching Cheung Road, etc.) and mass 9
transportation facilities (e.g. MTR and KCR)
Slopes affecting district or local distributors, rural roads types (A) and
(B) which are not sole accesses 9
Slopes affecting rural feeder roads and small roads not classified by
Transport Department, which are not sole accesses
Notes: (1) The above examples are for guidance only.
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(2) In assessing the economic consequence in the event of road blockage or closure due to a landslide,
due regard should be given to factors such as:
(a) whether the road is a sole access which has implications on the accessibility of emergency
vehicles such as fire engines and ambulances,
(b) the consequence to the facilities served by the access, and
(c) impact on alternative transportation routes and essential services.
Where the road lies beyond the expected influence zone of a landslide, the
consequence categories as given in Table 4.2 may be downgraded as appropriate. Reference
may be made to Figure 4.2 and WBTC No. 13/99 (Works Bureau, 1999b) for further guidance
on this.
4.3 FACTORS OF SAFETY
The recommended minimum factors of safety for design of new highway slopes and
stability assessment of existing highway slopes are given in Tables 4.4 and 4.5 respectively.
For a failed or distressed slope feature, the cause of the failure or distress must be