271117 Techtonic GeoTech Cooroy Mtn Rd

Mr Ken Freeman                                                                                17385-001-Rev0
                                                                                            27 November 2017




                                                                Approximate site location




Text Figure 2: Extract from Gympie Geological Map

The Bowler soil test comprised two boreholes advanced using machine augering techniques to a depth of
2.4 m BGL (below ground level). These encountered a mixture of medium dense to dense clayey sand,
and very stiff to hard, low to medium plasticity, sandy clays. These were both logged as being brown to
red-brown in colour.

Groundwater was not encountered in the Bowler Geotech holes, with soils described as moist.

Prior to the construction of the existing house, Bowler Geotech classified the site as Class M in
accordance with AS2870, with a predicted surface movement (ys) due to soil moisture content variation of
around 30 mm.

3.2   Subsurface Conditions - Tectonic Test Pit Investigation
Subsurface materials at the investigation locations consisted of mostly medium to high plasticity silty clay,
being firm to stiff to 0.5 m depth, becoming very stiff to hard below. Exceptions to this were at TP1 (proposed
garage extension), where medium dense silty sand was encountered to 1.3 m depth; and in TP4 where
around 1.5 m depth of fill was encountered. Mostly the natural materials were grey to pale grey mottled
yellow and orange brown, with some red-brown coloured soils north-east of the existing house.

Where excavator bucket refusal occurred, this was interpreted as rockhead, and was inferred as highly
weathered, very low strength rhyolite. Soils above the inferred rockhead were inferred to be residual
material.

3.3   Topography
As illustrated by the contours in Text Figure 3 on the following page, moderately steep slopes of 20° to 25°
(36% to 47%) are present in the southern part of the lot (the flanks of Mount Cooroy) with the gradients
becoming progressively gentler towards the north (10° to 12° (18% to 21%)). Four gullies are present within
the lot boundary, mostly running south-north, and not in close proximity to the existing house or proposed
construction areas.

The Bowler investigation report noted that the original ground slope at the site of the house was
approximately 25% (14°). Measurements taken on site by Tectonic using a hand-held inclinometer indicate
the natural slopes on the eastern side of the house site are up to around 20˚ (36%), becoming flatter to the




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