Slope Stability Report

Stability of Retaining Structures

Geotechnical stability of all proposed retaining structures must be carried out against sliding, overturning and global
slope instability. The retaining structures must also be stable against bearing capacity failure (or excessive base
settlements). Moreover, the retaining structure itself must be adequately designed against any potential structural
failures such as flexural failure or shear failure.




                                                                                                  B




                                                                                   Pa=Active earth pressure




                                    Pp=Passive earth
                                    pressure
                                                         O




Fig. 7: Typical retaining structure and the lateral earth pressure distributions

Figure 7 shows a typical retaining structure including lateral earth pressure distributions. The retained soil behind
the retaining structure will exert active lateral earth pressure if the retaining structure allows some lateral
movement; otherwise lateral earth pressure at rest (Ko condition) should be used during design and stability
assessments. The soil in front of the wall will cause passive earth pressure, as shown in Fig. 7.

All development applications involving retaining structures must assess the geotechnical stability and factor of
safety against the following:

a) Sliding caused by the active earth pressure and resistance by passive earth pressure and frictional force at the
base the retaining structure;

b) Overturning about the toe (point O in Fig. 7) as a result of driving moment caused by the active earth pressure
and resisting moment caused by the passive earth pressure, the self‐weight of the retaining structure and weight of
the retained soils behind the structure; and

c) Global slope instability considering a large slip circle passing through the underneath of the retaining structure
and the retained soils.

The stability assessment shall ensure that all retaining structures will achieve a factor of safety (FOS) > 1.5 against
sliding, overturning and global slope instability.

Referenced “Geotechnical Stability Assessment Guidelines JUNE 2007: Version 1.0 Gold Coast City Council” Section
5.2 Page 19.