Compiled Reference Document - MCU25/0020 (As Published)

6.4.2        Footing Options
For the anticipated approximate gross distributed building foundation pressure of up to 55 kPa under
the building, the adoption of strip and pad footings is not recommended as the settlement of foundation
soils would be excessive. Therefore, footing options that may be considered for the proposed building
include a well stiffened raft slab or piles. Discussion on raft slab and piled footing systems is given in
Sections 6.4.3 and 6.4.4 respectively.

6.4.3        Raft Footing Design
It is anticipated that a well stiffened raft slab footing system could be adopted to support the proposed
building provided that total and differential settlements, as estimated and given in Table 5, can be
accommodated. The raft would need to be designed to evenly distribute building loads throughout the
slab, including concentrated column loads. SCG has indicated that gross pressures beneath the
basement floor slab would be in the order of about 55 kPa.
Analysis indicates that settlements should generally within the feasible limits for a well stiffened raft slab
footing system. Further analysis should be carried out once structural design details are finalised to
confirm the above estimates remain valid. This should also include finite element analysis to resolve
soil/structure interaction with input from the structural designer to accurately calculate
stresses/displacements and subgrade/slab reactions. Resistance to uplift from hydrostatic pressures
should also be considered by the design RPEQ. Piles or tie down anchors to resist uplift may be required.
Should the anticipated settlements preclude the use of a well stiffened raft slab, piled footings would be
required (Ref. Section 6.4.4). As outlined above, concentrated wall/column loads or peak perimeter
pressures exceeding 55 kPa would also need to be transferred using piled footings.
Excavations for the basement are expected to expose mostly medium dense to very dense
sands/indurated sands. The raft subgrade must be inspected by a geotechnical RPEQ to confirm the
foundation materials and allowable bearing pressure, and to advise on treatment of any unsuitable zones
(if encountered).

6.4.4        Piled Footing Design
Where anticipated settlement cannot be tolerated in a stiffened raft solution or in areas with
concentrated/elevated peak pressures, a piled footing system would be required. Considering the likely
order of column loads to be supported, piles would could be socketed into the dense to very dense
sands at about 7 m BGL. Piles may be designed using an allowable end bearing pressure of 1 MPa in
dense or very dense sands.
It is envisaged that steel screw piles could be adopted for the development. The use of bored piles,
without the use of steel liners and dewatering equipment, would be precluded by the presence of
shallow groundwater and loose sands near surface. Driven piles would likely not be suitable given the
suburban environment (e.g. noise disturbance) and potential vibratory effects on adjacent structures
(residences and underground services). Grout injected CFA piles could also be considered.
If steel screw piles are adopted, it will be important to ensure close supervision of installation, as piling
may not encounter sufficient drilling resistance (from torque measurement) in dense sands at the
suggested founding depth, and piles could extend to much greater depth than necessary.
It is therefore recommended that site specific dynamic load pile testing should be conducted. Where
tension or compression capacity developed in the footings is critical for the future structure (e.g.
resistance to uplift forces etc.), then cyclic load tests (including measurement of deflections under

Geo-environmental Investigation Proposed Residence
4 June 2025 | 25040-001-Rev1                                                                                    16