Appendix B- Geotechnical Investigation

Project No. 115-17158
April, 2015
Ref: 1-17158, 2015-04-08, BR VER 1                                                                                 Page | 7
John Jamieson – GEOTECHNICAL INVESTIGATION - Proposed Residence, 38 Park Crescent, Sunshine Beach




           5.4.2      Deep Foundations

It is considered that the most appropriate piling system would be that which involves the
least amount of ground vibration during construction. Therefore, continuous flight auger
(CFA) grout (or concrete) piles or screw-in piles are considered to be suitable. Conventional
bored piles are considered unsuitable for construction of piles, as the excavations would
collapse.

However, specialist piling contractors should make their own assessment of pile type and
founding levels/length considering pile load requirements and subsurface conditions.

It is recommended that piled foundations should extend at least 1.0m into the dense sand,
(as a minimum).

It is recommended that the deep foundation system on this project be designed in
accordance with AS 2159-2009 'Piling - Design and Installation'. This code uses the limit
state design method.

Compressional Capacity

The design of a single pile or a pile group must be such that both the geotechnical design
strength Rd,g and the structural design strength Rd,s are greater than or equal to the design
action effect Ed*, ie.

                                 Rd,g  Ed and Rd,s  Ed

The design geotechnical strength (Rd,g) can be calculated as the ultimate geotechnical design
strength (Rd,ug) multiplied by the geotechnical strength reduction factor Øg.

The design of piles in cohesionless soils (sand) may be carried out using the following
method:

                      R d,g  R d,ug   g                       g       -     Refer       Table   4.3.2   (c)   AS2159
                      R d,ug  Q b  Q s                          ultimate pile resistance

           where:

                      Q b  A b  p d  (N q  1 )                ultimate base resistance
                      Q s  A s  p d  K s  (tan  )            ultimate skin friction
                      As        area of pile shaft
                      Ab        area of pile base
                      pd        effective overburden pressure at depth d (p d    d )

                      where                Loose = 17kN/m3
                                            Medium Dense = 18kN/m3
                                            Dense = 19kN/m3