Attachment C - Soil Survey Report · MCU18/0013

Project No. 1-20119                                                                                                           Page | 27
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach




the retaining walls are expected to be surcharged (e.g. by footings, traffic loads, sloping ground
surface, etc.) Soil Surveys Engineering should be contacted to provide a recommended lateral
earth pressure distribution.


                                             TRIANGULAR DISTRIBUTION
                         Lateral Earth Pressure                             Lateral Earth Pressure due to Surcharges




           H                   K(H-hw)



                    hw


                                     KH+hww(1-K)

                K = appropriate earth pressure coefficient
                H = Vertical height of the wall                                          UDL                  Point Load or
                Hw = Height of design water table                                                             Strip Footing
                 = Soil bulk density (kN/m3)
                w= water bulk density (kN/m3)

                                                                   FIGURE 5

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
(unfactored) for assessment of lateral earth pressures are outlined in Table 8.

Any backfill placed behind the wall should be loose granular material. The backfill should not
be heavily compacted since research has shown that compaction can raise the earth pressure
to above the 'at rest' pressure.

Adequate surface and subsoil drainage should be provided for all retaining walls on the site.
Cut-off / interceptor drains should also be provided around the high side of the wall to ensure
stormwater runoff from the area above the wall is suitably diverted.

The placement of a filter fabric between the retained soil and the drainage material (e.g.
granular backfill) for protection against silting of the drainage material is recommended. The
outlets to subsoil pipe drains must be located beyond the ends of the walls and connected to a
proper drainage system. It is suggested the pipes be wrapped in filter fabric to minimise silting.