Appendix B - Geotechnical Assessment · OPW23/0179

 Project No. PG-10375                                                                               Page | 10
 June 2023
 Ref: PG-10375, 2023-06-09, LTR VER 1
 Michael Cullen – Geotechnical Investigation - Proposed Residence, 128 Gympie Terrace, Noosaville




  v.       Where required, replace the over-excavation with “clean” sand and compact
           in layers to the design founding level. The founding soils should be compacted
           to a minimum Density Index of 75% (in accordance with AS 1289 5.6.1).

Foundation Design Parameters

For footings founded 3m below the ground level, an allowable bearing capacity of
300kPa could be adopted in the indurated sand and 200kPa in the recompacted
sand above the indurated sand, following confirmation that a minimum Density Index
of 75% is present below the footings.

If the exposed sands are disturbed or loosened during the excavation operation, they
should be recompacted. Consideration should be given to placing a 50mm thick
(minimum) concrete binding layer across the footings, immediately following
excavation.

Settlement Potential

Settlements from a 30kPa raft type foundation system founding 3.0m below existing
ground level have been calculated to be in the order of 15mm with anticipated
differential settlements of between 25% and 50% of the calculated total settlement
for pad footings founded at a similar depth.

A modulus of subgrade reaction (k) of 6 to 8 kPa/mm could be adopted for
preliminary raft design. The value should be confirmed as raft loads are refined.

The settlement will occur as “immediate” settlement as the building loads are applied.

Hydrostatic Uplift Forces

For a fully tanked basement, hydrostatic uplift forces should be considered in the
design. It is recommended hydrostatic uplift forces in groundwater levels to at least
RL1.5 to 2.0 be taken into consideration on this site and checked for the Q100 flood
condition.

   12.1Deep Foundations

Where the structure extends beyond the basement, consideration could be given to
adopting a deepened foundation system founding into a consistent founding stratum
of the main raft. Alternatively, a high level footing system could be adopted, with
appropriate ground improvement works, provided the structure can be suitably
detailed to tolerate the potential differential settlement between the structures.

Where the extent of over-excavation required or the foundation treatment is not
considered practical, a deep foundation system could be adopted.

Screw piles or possibly driven timber piles could be considered for the support of the
proposed structure.