Attachment 2 - Geotechnical Stability Assessment

Project No. PG-2096                                                                                                      Page | 9
May 2022
Ref: PG-2096, 2019-02-21, GR VER 4
Clare Design – Geotechnical Stability Assessment - Proposed Residence, 22 Arakoon Crescent, Sunshine Beach




                                                                                                 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.

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
compaction be required, then wall stresses will be well in excess of Ko and
temporary propping should be used.

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.