geotech report · 132003.220660.5

Any poorly compacted surficial fill and very loose natural sands encountered in the investigation may extend
across the site boundaries. We therefore advise that sudden stop/start movements of any tracked
equipment be avoided in order to reduce transmission of ground vibrations to the adjacent steep fill batter
slope to the north-west within the neighbouring road reserve as this could cause localised instability.



6.3.3 Groundwater Seepage
Groundwater seepage was not encountered in the previous ASI boreholes and there were no traces of
seepage noted during the current investigation when extracting the DCP rods. Some ephemeral seepage
inflows may be encountered in any excavations particularly after periods of heavy or prolonged rainfall. In
general, we expect that inflows, if any, to be of very small volume and managed by infiltration into the sandy
subgrade. Inspection and monitoring of groundwater seepage during excavations is recommended, so that
any unexpected conditions, which may be revealed can be incorporated into the drainage design.



6.4   Temporary Excavation Support and Retention
Temporary batter slopes through the sandy soil profile no steeper than 1 Vertical (V) in 1.5 Horizontal (H)
may be achievable within the site geometry over the northern and western sides of the excavation provided
any existing landscape retaining walls are removed.

Some instability of temporary sand batters may occur at, or below, the level of any groundwater seepage
should it occur, especially after rain periods, and sand bagging may be required to stabilise the lower portion
of these batters.

Stockpiles of construction materials, excavated materials, existing footings, etc. must be kept well clear of
the batter crests to avoid surcharging the slopes.

Where battering cannot be accommodated within the site geometry, or is not preferred, a full depth
engineered piled wall retention system must be installed prior to excavation commencing. Due to the close
proximity of the northern side of the existing house and the presence of poorly compacted sandy fill and very
loose sands, deflections will need to be reduced. Adjacent to the existing house and any landscape retaining
walls that are to remain, the piles may need to be provided with corbels to support the existing high level
house footings and/or temporary propping of the heads of the piles provided. Considering the maximum
retained height will be about 1.5m it is likely that cantilever piled walls will be suitable where adjacent
structures are not located within the ZoI, as defined above pending confirmation by the structural engineer.
The piles would need to extend to sufficient depth below bulk excavation level (BEL) to satisfy stability
considerations. The structural engineer must design the shoring walls, calculate the potential deflections and
make an assessment of the effect of the deflections on nearby structures. The structural engineer must then
make an assessment as to whether the shoring walls must be stiffened and/or braced, and whether any
underpinning of nearby structures are required.




32032URrpt                                        13