Appendix D Geotechnical report · MCU18/0013

Project No. 304-2014

November, 2004 Page 14
Given that the excavation is expected to be up to 6m deep, a braced retaining wall will be
required. This retaining wall should be installed prior to excavation to ensure stability of

the sandy profile.

Several types of retaining walls could be employed including steel sheet piles, contiguous
CFA piles or diaphragm wall. Each of these have relative advantages and disadvantages
(technical and economic) which are best evaluated at the detailed design/tender stage.

6.5.2 Pressure Distribution

In designing the retaining wall, consideration should be given to the following:-

* For cantilever walls, which allow some movement at the top, (ie. at least 0.001H in
sand) the active case (Ka) applies with a triangular distribution in both the short and
long term situations.

* For cantilever walls which cannot tolerate this movement, the at rest case (Ko)
applies with a triangular distribution in both the short and long term situations.

* For structurally braced walls the wall design should be checked for both a
trapezoidal (short term conditions) and triangular distribution with Ko values (long

term conditions).

The pressure distributions as referred to above are shown in Figures 2 and 3. The
parameters selected for use in the figures are dependent on the preconstruction
geometry of the face being retained. Where the material has been cut using the
recommendations (or a flatter) as outlined in section 6.2.7, the backfill parameters will

control. Where a steeper angle is used the earth parameters will control.

The lateral pressure distributions shown in Figures 2 and 3 include hydrostatic pressure
and show typical surcharge loadings pressure distribution. It is recommended that where
the retaining walls are expected to be surcharged (eg. by footings, traffic loads, sloping
ground surface, etc.) Soil Surveys Engineering should be contacted to provide a

recommended lateral earth pressure distribution.

As a general guide (using an elastic model) line loads located 2.5H away from the wall
(where H is the wall height) results in lateral forces of less than 10% of the line load.

Parameters for assessment of lateral earth pressures are outlined in Table 6.

 

# SOIL SURVEYS ENGINEERING