Development Application Part 2 of 2 - Geotech Report and Plans - OPW13/0816

                                                -4-


                                                                                   Job No. 213-15522
                                                                               ,


 For design purposes, geotechnical design strengths
                                                         (Rct,g) of 500kPa in end bcc:-:r.g C~~
 40kPa in lateral capacity would be available at not less than .5m embedment into dense. or
 better, sand strata. Uplift resistance parameters can be provided once a piling system has
 been considered.


 The use of raked piles could also be considered for additional lateral
                                                                              capacity. Buttressing
 revetment rock against the revetment wall, to at least HAT levei, would also contribute to the
 passive resistance of the wall, however, it is not recommended the                passive resistance
 afforded by the revetment rock be considered in the wall design.


 A working platform would be required for the installation of
                                                               piles and construction of a
 suspended footing system to support the replacement revetment/retaining wall.

 Options to provide a suitable construction pad include reinstating the revetment batter with
 clean sand utilising a berm of revetment rock placed along the creek
                                                                            frontage
                                                                               to         the
                                                                                          support
 sand backfill. Refer Option 1 I Figures 1A and 1B.


 It is recommended clean sand be used as wall backfill with a
                                                              drainage layer comprising not
 less than a 300mm width of 20mm clean, free draining aggregate encased in a             ie.
                                                                                  geofabric,
Terrafix SP360 or similar, placed      immediately behind the wall and to within 300mm of the
 backfill surface. Refer Figure 1 C.


It is essential the wall be constructed with adequate drainage holes to ensure efficient and
long term drainage of the wall backfill. However, it is recommended the replacement wall be
designed for full height hydrostatic pressure.

The following retaining wall soil design parameters are recommended for the
                                                                                         replacement
wall.


        Backfill Unit Weight                                   18kN/m3


        Earth Pressure Co-Efficient-Active (Ka)0.36 (280internal friction
                                                                            angle)

It is suggested piling works be carried prior to stabilising the creek bed and revetment batter
with rock protection in order to inhibit possible impediments to piling works.             it is
                                                                                       However,
essential the stabilisation works proceed promptly to inhibit further
                                                                        degradation of the revet-
ment profile, which is currently encroaching to within 2.0m of the residence, and
                                                                                            possible
loss of foundation support at the rear of the residence.




                                                ’#SOIL SURVEYS ENGINEERING PTY LIMITED
1-15522,2013-09-20, LR VER 0