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DEPARTMENT OF INFRASTRUCTURE ENGINEERING
CVEN90050 Geotechnical Engineering
Retaining walls – Assessment No. 5 (Group Assignment)
Group Submission
This assignment is based on a slightly modified version of Example 3 from AS5100.3 S1-2008
as worked through in the Tutorial. In the tutorial the toe depth was assumed. The task is to
write a spreadsheet that will enable calculation of the factor of safety against rotation about a
specified prop level for varying toe levels and the resulting prop load, shear force diagram and
moment diagram. Several methods of determining these diagrams are presented in the
AS5100.3 example. The method you are to employ is to assume:
• A free earth support limiting equilibrium method where the strength factor is applied to
the passive resistance in front of the wall only (i.e. as given in the Tutorial and Lecture).
• Mobilised passive resistance is to be assumed to be the reduced by the actual factor of
safety calculated for the selected toe level.
A propped cantilever sheet pile is installed to retain a 7.9 m deep excavation (Figure 1). The
ground water level was found to be 1 m below the ground surface. A pump station is set up at
the bottom the excavation to make sure the water level is kept 1.1 m below the proposed
excavation level. A surcharge of 20 kPa is applied at ground level. Soil properties are derived
from advanced laboratory testing and are shown in Table 1. The sheet pile can be considered
as a temporary retaining structure with a maximum service life of 1 year.
Table 1
Soil
Layer
Unit Weight
(kN/m3)
Drained Friction
Angle (°)
Drained
Cohesion (kPa)
Layer I
20
30
0
Layer II
22
28
10
