Reference Document - MCU25 0101 (As Published)

 Project No. PG-13872                                                                                               Page | 8
 August 2025
 Ref: PG-13872, 2025-08-14, GR VER 1
 Stephen & Jane Struss – Geotechnical Investigation - Proposed Residence, 28 Kingfisher Drive, Peregian Beach




10.0 PERMANENT RETAINING WALLS

Basement walls should be designed using a pressure coefficient for the at rest case of
K0 = 0.5.

Unit wall force P is given by:-

                       P           =           0.5 K0  H12 (kN/m run of wall)

Passive resistance at the base of the wall can be calculated from:-

                       P           =           0.5 Kp  Hw2

           where Kp                =           3.0 (ignores wall friction effects) for loose sand
                                               3.25 for medium dense sands
                                               3.39 for dense to very dense sands

                       Hw          =           front face of wall contributing to passive resistance (m)

For the sliding resistance calculation, the angle of friction for sand () compacted to
not less than 75% density index can be taken as 32° for walls with a key. For walls
                                                                                                                ଶ
without a key, the angle of friction for sliding resistance should be taken as ଷ  or 21°.

11.0 BUILDING FOUNDATIONS

Given the encountered subsurface profile, a high-level footing system would
generally be suitable for the support of the proposed structure, with appropriate
ground improvement works and due consideration of the potential hydrostatic uplift
forces.

Assuming an excavation depth of between 2m and 4m for the basement, provided
the founding soils are compacted to a minimum Density Index of 75% for a minimum
depth of 1m below the footings, an allowable bearing capacity of 225kPa could be
adopted for the foundation design.

This classification could be achieved through the over-excavation of the founding
soils, compaction of the exposed material and the replacement of the excavation
using “clean” sand.

It is strongly recommended that if a high-level footing system is to be adopted,
sufficient “clean” sand from higher in the excavation profile be stockpiled on-site, to
allow for the replacement of the silty sands at the founding level.

To enable the required ground improvement works to be undertaken, the following
earthworks operation is recommended:

   i.      Install the temporary retention system and dewatering system.

  ii.      Dewater the site to at least 0.7m below the excavation level.