Appendix G - Geotechnical Report

Total Concept Homes                                                                                  20332-001-Rev0
                                                                                                   15 December 2020

          An upper layer of residual, medium plasticity, stiff silty clays to between 0.6 m and 0.7 m BGL;
           overlying;
          Extremely weathered (XW) material comprising stiff to very stiff silty clays, to between 1 m and
           1.4 m BGL; then grading to
          Weathered Phyllite, inferred to be very low to low strength to the borehole termination/target
           depths.

Groundwater seepage was not encountered during the drilling of either borehole BH1 or BH2, with all
soils being described as “dry.”
The site was classified by Ground Drill as Class P in accordance with AS2870-2011 due to the presence
of mature trees. In not for this factor the site would have been classified Class M with characteristic
surface movements (ys) of up to 35 mm reported by Ground Drill.

Along the southern edge of the existing access track, and in the cutting behind the existing residence
exposures of weathered rock were observed. These were noted to consist of moderately weathered, very
low to low strength, pale yellow brown phyllite; which had a well developed foliated fabric. To the south-
east of the existing residence this was interlayered with XW materials, although the lateral extent of this
was not clear, and such materials may be restricted to the near-surface of the exposed rock mass.

A view of the exposed weathered rock above the highest section of proposed earthworks filling is shown
below in Text Figure 4.




Text Figure 4: Exposed weathered phyllite in cutting above highest section of earthworks filling

2.2       Topography
As illustrated in Text Figure 5 on the following page, the wider area around the site consists of a series of
approximately parallel ridgelines and gullies, aligned east-west. The ridgelines within the subject allotment
lead east from Black Mountain Range Road, which traces a crest forming a drainage divide between
eastward and westward draining creek lines.

Just off Black Mountain Range Road, to the south-west of the overall existing allotment, a rounded gully
head was present, with sideslopes ranging from about 25° (47 %) at the site entrance to between 15° and
20° (27 % and 36 %) nearer the existing residence. Minor existing cut and fill earthworks had been
undertaken sidelong to the slope to facilitate the existing track, being 1 m to 1.5 m depth and around 1 m
height respectively. Below the existing residence, to the north, a series of cut terraces had been formed for
horticultural purposes. These were in the order of 2.5 m width, with cut batters of around 0.6 m depth or less.
Across the existing earthworks features on site, no signs of significant slumping were observed.




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