Rfi - PG-2096, 2022-11-03, Gr Ver 3

 Project No. PG-2096                                                                                                            Page | 9
 March 2023
 Ref: PG-2096, 2022-11-03, GR VER 3
 Keith & Jeannette Ince – Geotechnical Stability Assessment - Proposed Residence, 22 Arakoon Crescent, Sunshine Beach




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 3.


                                                                                                FIGURE 3
                                                        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.

TABLE 3                EARTH PRESSURE COEFFICIENTS (NON-SLOPING CREST BACKFILL)

                                                           Unit                 Friction
                                                                                                 Active             At Rest   Passive
 Material                                                  Weight               Angle
                                                                                                 Ka                 Ko        Kp
                                                           (kN/m3)              (degrees)
                   Loose                                   18                   26               0.39               0.56      2.56
 Sands             Medium Dense                            18.5                 30               0.33               0.50      3.0
                   Dense                                   19                   32               0.31               0.47      3.25

Preference should be given to adopting thin soil layers and using small hand-
controlled compaction equipment during backfilling against retaining walls. This is in
order to limit the stress applied to the walls during construction. Should heavy