Volume 6 – Geotechnical Manual, Site Investigation and Engineering ...

Chapter 7 RETAINING WALL
∆p s
= K q s
(7.13)
where ∆ps
qs
K
= increase in lateral earth pressure due to the vertical surcharge load
= vertical surcharge load applied at the ground surface,
= appropriate earth pressure coefficient.
When traffic is expected to come to within a distance from the wall face equivalent to one-half the
wall height, the wall should be designed for a live load surcharge. The standard loadings for
highway structures in are expressed in terms of HA and HB loading as defined in BS 5400 : Part 2 :
1978. In the absence of more exact calculations, the nominal load due to live load surcharge may
be taken from Table 7.2.
Table 7.2 Suggested Surcharge Loads to be Used in the Design of Retaining Structures
Road class
Type of live loading
Equivalent
surcharge
Urban trunk
Rural trunk
(Road likely to be regularly used by
HA + 45 units of HB
20kPa
heavy industrial traffic)
Primary distributor
Rural main road
HA = 37 ½ units of HB
15kPa
District and local distributors
Other rural roads
HA
10kPa
Access Roads, Carparks
Footpaths, isolated from roads
5kPa
Play areas
Note : 1. It is recommended that these surcharges be applied to the 1 in 10 year storm condition.
2. For footpaths not isolated from roadways, the surcharge applying for that road class
should be used.
(Source: Public Works Department, 1977)
Point loads, line loads, and strip loads are vertical surface loadings that are applied over limited areas
as compared to surcharge loads. Hence, the increase in lateral earth pressure used for wall system
design is not constant with depth as is the case for uniform surcharge loadings. These loadings are
typically calculated by using equations based on elasticity theory for lateral stress distribution with
depth and are as shown in Table 7.13. Lateral pressures resulting from these surcharges should be
added explicitly to other lateral pressures.
March 2009 7-15