Slope Stability Assessment

Paul & Janelle DeSouza                                                                            22198-001-Rev1
C/- Sarah Waller Architecture                                                                        25 July 2022




               Text Figure 10: Footing depth required to minimise risk of undermining and surcharging

Footing bases must be cleaned following mechanical excavation to expose undisturbed materials over the
full base area. Due to the depth of footing excavations required, the piling contractor must have a ‘mud
bucket’, or similar, to enable clean out of pile sockets. With the expectation that socketing to weathered
sandstone is required, contractors should also allow for a suitable rock auger for such material penetration.
A suitably qualified and experienced engineer should inspect the footing excavations to confirm appropriate
foundation materials and cleanliness prior to pouring concrete.

If any ground conditions encountered during construction are found to differ from those noted above,
Tectonic and Ground Drill must be notified immediately and an inspection carried out to determine if changes
to footing design are required.

4.4   Drainage
Surface diversion drainage should be constructed above the crest of any cut or fill embankments and
retaining walls (e.g. grassed or landscaped swales or diversion mounds). Adequate site drainage must be
installed to ensure that stormwater is directed away from building walls and footings, and also not allowed to
flow over fill embankments in an uncontrolled fashion (e.g. as overflow run-off from roof gutters, along the
surface of any fill embankments beneath the house, etc.).

Subsurface drainage must be installed behind any retaining walls (e.g. slotted ‘aggi’ pipe wrapped in filter
‘sock’ placed in gravel backfill). Depending on matters such as the extent of drainage installed and site-
specific groundwater conditions, the designer must make an assessment of hydrostatic pressure to be
accounted for in the design of the retaining structure.
All excess stormwater collected around the residence (including overflow from rainwater tanks and the
swimming pool) should be directed downslope by pipes or lined channels to discharge into a rock-lined
contour drain, stacked rock weir, or similar, located at least 10 m down slope of any fill or structures,
including the land application area proposed to the north of the residential structures (generally to the north-
east or north-west). Subsurface disposal of stormwater must not be undertaken (including infiltration
pits).




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