Attachment 2 - Geotechnical Stability Assessment

Project No. PG-2096                                                                                                       Page | 8
May 2022
Ref: PG-2096, 2019-02-21, GR VER 4
Clare Design – Geotechnical Stability Assessment - Proposed Residence, 22 Arakoon Crescent, Sunshine Beach




TABLE 2                DESIGN VALUES FOR LATERAL PILE CAPACITY CALCULATION

                                                                                                             Bulk Density 
                              Material                                               Design Kp
                                                                                                                (kN/m3)
                                               Loose                                      2.56                     18
            Sands                           Medium Dense                                  3.0                     18.5
                                               Dense                                      3.25                     19

Should a 'working stress' approach be adopted, a factor of safety of between 2.5
and 3.0 should be adopted.

Lateral capacity may be achieved through the use of raked screw piles etc. if
required.

Construction Considerations

Given the non cohesive soil conditions encountered on site, it is likely that a bored
pier type foundation system will not be appropriate as side wall collapse of the piers
is likely to occur. Appropriate piling solutions could include CFA piles or possibly
screw piles, however screw piles are unlikely to provide significant lateral capacity
and a combination of vertical and raked piles may be required.

During construction, all piles must be inspected by a geotechnical engineer to
confirm the geotechnical strength parameters presented in Table 1 and Table 2 and
to check the capacity of the piles.

8.0 RETAINING WALLS

Retaining walls up to 3m in height may be required as part of the development.
Walls should be specifically engineer designed in accordance with AS 4678-2002
(Ref 9).

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 1.