RFI - Attachment C - Slope Stability Assessment and Geotechnical report · MCU20/0026

Project No. 1-22543                                                                                                          Page | 19
June, 2020
Ref: 1-22543, 2020-05-20, BR SSA VER 1
Sanya Holdings – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 40 Park Crescent, Sunshine Beach




The base of all pad and strip footings founding in sand should be individually re-compacted
using a vibrating plate compactor prior to placement of reinforcing steel and concrete as soils
may be loosened during the excavation process by machinery action.

Should any loose areas be encountered in the footing excavations, the density of these areas
must be improved. Dynamic cone penetrometer (DCP) tests should be carried out to confirm
the adequacy of the founding soils. Note that it may be necessary to use formwork to prevent
trench side collapse in the sand profile.

It should be noted that any relevant stability recommendations contained in Section 5.0
will also apply to high level foundations. Also should excavations exceed 0.5m in depth
they may need to be assessed for stability on a case by case basis.

Where necessary, footings deeper than 300mm may be made up with mass concrete poured to
the underside of the footings, or alternatively, footings may be constructed over mass concrete
filled, backhoe excavated pedestals.

      6.2.5            Deep Foundations
General

A deep pile system may also be utilised for the proposed structure and for retention systems on
the site. The choice of suitable pile types should be made from non-vibration piling methods.

Push piles, continuous flight auger (CFA), bored piles or screw piles could be considered as
suitable pile types, although the construction of the bored piers may be problematic in loose
sand, where collapse of the pile hole is likely. It is recommended specialist piling contractors be
consulted to make their own assessment of pile types considering subsurface conditions and
pile load requirements. Access onto the site for piling machinery must also be considered.

Depending on the load requirements, and the piling contractors design, it is recommended that
the piles are founded in material which is at least medium dense, and at a minimum depth of
3m below existing ground surface.

Compressional Capacity

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.

In the limit state design method the following must be taken into account:-

          Considering limit state analysis (AS 2159-2009), the design geotechnical strength Rd,g is
           calculated by multiplying the ultimate geotechnical strength Rd,ug by the geotechnical
           strength reduction factor Øg, i.e.

                                               Rdg = Rd,ug g
          Ultimate strength - the design of a single pile or a pile group must be such that both the
           design geotechnical strength (Rd,g) and the structural strength (Rd,s) are greater than or
           equal to the Design action effect (Ed) i.e.

                                               Rd,g ≥ Ed and Rd,s ≥ Ed

                                                                                                               SOIL SURVEYS