geotech report · 132003.220660.5

4.2   Subsurface Conditions
Based on our review of the provided ASI ‘Soil Test Report’ and our DCP test results, we conclude that the
encountered subsurface profile comprises an intermittent limited thickness of fill with the Pleistocene age
sand dune deposits either underlying the fill or present from surface level. Groundwater and bedrock were
not encountered within the depth of our investigation and the previous ASI investigation. A summary of the
pertinent subsurface conditions is presented below and for further details reference should be made to the
previous ASI ‘Soil Test Report’ and the attached DCP test results.

Fill
ASI BH1 encountered poorly compacted sandy fill which extended to 0.4m depth. We note that the ASI
investigation was completed before the existing house and surrounding landscaping was completed so it is
likely that greater thicknesses of fill are present in localised areas of the site where flat terraces have been
formed on the downslope sides of the property and supported by landscape retaining walls. We also note
that during the fieldwork, the owner indicated to our geotechnical engineer that in the area of the proposed
lift pit, excavations had been completed to accommodate the original house construction, and was backfilled
on completion of construction. On this basis, and assuming a sandy fill profile, we have interpreted the results
of DCP101 to indicate poorly compacted fill.

We note that in the absence of formal records of placement and density test results and considering the fill
has been assessed to be poorly compacted, the fill is regarded as ‘uncontrolled’ as defined in AS2870-2011
‘Residential slabs and footings’ (AS2870-2011).

Natural Dune Sands
In the ASI boreholes, natural dune silty sands were encountered below the fill (BH1) or from surface level
(BH2) and extended to the termination depth of the boreholes at 9.3m. Based on our interpretation of the
ASI DCP test results the sands were initially of very loose relative density improving to loose below about
1.5m to 1.6m depth. Below about 3.5m depth (BH1) and 3.2m depth (BH2) the sands improved to medium
dense and extended to the respective DCP test termination depths at 4.4m and 3.5m.

Assuming a similar subsurface profile, the results of DCP101 and DCP102 have been interpreted to indicate
very loose silty sands from below the fill (DCP101) and from surface level (DCP102). Below about 1.4m depth
the relative density improved to loose, then medium dense below depths of about 2.5m (DCP101) and 2.1m
(DCP102) to the termination depth of the DCP tests at 8m.

Groundwater
No groundwater was noted during or on completion of auger drilling the boreholes during the ASI
investigation and in our current investigation, the DCP rods were ‘dry’ immediately after extraction.



4.3   Summary of Observations
The summary of observations which follow in Sections 4.3.1 to 4.3.4 are to be read in conjunction with the
attached Figure 2.

32032URrpt                                         4