RFI - slope stability reporting

RECOR Pty Ltd                                                                                  22393-001-Rev0
                                                                                               26 October 2022

The boreholes encountered relatively consistent subsurface conditions, summarised as follows:

          Fill (borehole BH1 only) – comprising loose silty sand to 0.4 m BGL; then or from the ground
           surface
          Natural Sands – initially comprising loose silty sand and poorly graded sand to depths between
           1 m and 1.2 m BGL, then becoming medium dense to the borehole termination depths.

DCP testing extended below the borehole termination depths, with inferred dense (or denser) sands
indicated at depths between 3.3 m and 4 m BGL.

Groundwater was not encountered during drilling of the boreholes, with the soils being moist.

2.2       Topography
During the site walk-over, topographic features specific to the site were noted, and ground slopes were
recorded using a hand-held clinometer. As illustrated in Text Figure 4, the site is located on the northerly
facing flank of an ancient sand dune, which crests about 100 m to the south.
The natural surface profile at the site had been interrupted by historic landscaping and residential
construction. Based on a visual appraisal it appeared that cut and fill earthworks in the order of about 1.5 m
depth/height had been previously undertaken, most of which were supported by retaining walls or structural
residential walls.

Inferred natural ground slopes surrounding the residence and along Southern Cross Parade typically were in
the order of about 8° to 12°, which is the assumed natural gradient across the site prior to residential
construction. The rear of the property had been terraced, with low height timber sleeper walls (<1 m high)
supporting relatively level platforms. At the time of the assessment an unretained cutting about 2 m high
was observed on the downslope property adjacent to the north-eastern corner of the site. This cutting was
battered at about 70° and exposed sand.




                                                     Subject Site




Text Figure 4: Ground surface contours, 1 m spacing (courtesy NC interactive mapping)

Site conditions at the time of our investigation are shown in Text Figures 5 and 6 overleaf.




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