Geotechnical Stability Assessment · MCU19/0008

Project No. PG-2096                                                                                                         Page | 8
April 2019
Ref: PG-2096, 2019-02-21, GR VER 2
Andrew and Michelle Douglas – Geotechnical Stability Assessment - Proposed Residence, 22 Arakoon Crescent, Sunshine Beach




8.0 RETAINING WALLS

Retaining walls up to 3m in height may be required as part of the development.
Walls should be specifically engineer designed in accordance with AS 4678-2002
(Ref 9).

It is recommended that all retaining walls be drained for full height in order to
minimise hydrostatic pressure build-up behind the wall. Additional guidelines on wall
drainage are provided in Appendix G of AS 4689-2002.

The design of flexible and rigid retaining walls could be undertaken using a triangular
pressure distribution and the earth pressure parameters given in Table 3. Flexible
walls are those which are free to rotate or tilt (such as cantilevered walls) and should
be designed using active (Ka) earth pressure coefficient. Rigid walls are those which
are restrained against rotation or tilt (i.e. single anchored/propped walls) and should
be designed using the at-rest earth pressure (Ko) and a trapezoidal pressure
distribution as per Figure 1.




                                                                                                FIGURE 1
                                                        0.25H




                                                                            H
                                    0.4  H




                                                         0.25H

                                                                                              KH
                                Trapezoidal                                                Triangular




Passive resistance (Kp) at the toe of the wall should be ignored in the zone where
future disturbance (e.g. services trenches) could occur.

The effects of surcharge in the retained zone should be included by multiplying the
vertical pressure developed by the surcharge by the appropriate lateral earth
pressure coefficient. Allowance should also be made for the surcharge due to
sloping crests if applicable.