Appendix G - Geotechnical Report

Total Concept Homes                                                                             20332-001-Rev0
                                                                                              15 December 2020

4.0        RECOMMENDATIONS
General recommendations to help maintain the stability of the site are given in the document Some
Guidelines for Hillside Construction, which is attached. This document should be referred to by those
preparing the concept and designs for future residential development at the site.

4.1       Site Layout and Geotechnical Constraints
Preliminary operational works plans (Ref. Section 2) were available for review at the time of this assessment,
however no bulk earthworks or building design details were are available regarding the proposed residence.
We understand that future building works would be located proximal to the area indicated in Text Figure 2
(not including areas for effluent disposal).

There should generally be no limitations on the methodology adopted for the future residence e.g. low set or
high set construction, or a split level structure built ‘in to’ the existing slope profile, however earthworks
should be limited to cut and fill of up to 1.5 m high/depth.
The general building location denoted in Text Figure 2 on the future subdivided allotment are considered
suitable from a slope stability viewpoint, although this should not encroach on the break of slope present to
the north and south, where ground slopes around 20° (36 %) were noted. Tectonic must be consulted to
assess the impacts on slope stability if development is proposed elsewhere on the site or if cut or fill
earthworks are to exceed 1.5 m in height/depth for the residence.

For the proposed driveway alignment, given the moderately steep to steep ground slopes present over
ground to the northern edge, all fill embankments >0.5 m height should be retained, and this is shown as the
intent on the supplied drawings (Ref. Section 2).

4.2       Earthworks
In construction areas, all vegetation, tree stumps and large roots must be ‘grubbed out’, existing uncontrolled
fill (e.g. along the proposed driveway alignment) with any organic rich topsoil stripped from the site. It is
recommended that subgrades be proof rolled using a minimum 4 tonne rubber tyred vehicle or drum roller to
identify any ‘soft spots’. Any such soft spots should be overexcavated and replaced with compacted select
fill.

Although trafficability should generally be good in ‘dry’ conditions, the soils could be subject to strength loss
from repetitive vehicle loading (particularly from rubber tyred plant) or if they become wet. Due to the
potential for poor trafficability during and after wet periods, placement of a minimum 150 mm thick granular
working platform may be required, particularly along access ways.

Fill materials should be compacted at moisture contents within the range of -2 % to +2 % of optimum
moisture content for Standard Compaction. Confirmatory compaction testing must be carried out at regular
intervals and further details for control and testing of fill are given in Australian Standard AS 3798-2007
Guidelines on Earthworks for Commercial and Residential Developments.

Fill (site won and imported) should have a maximum particle size of 100 mm for an uncompacted layer
thickness of 200 mm; and shall be compacted by repeated rolling with a roller to achieve a dry density ratio
of at least 95 % of the Standard Maximum Dry Density for cohesive soils, or 70 % Dry Density Index for any
imported cohesionless soils. Topsoil must not be re-used as structural fill, but may be used for landscaping.

Any imported fill should comprise a good quality material meeting the following specifications:

          Soaked CBR ≥ 10 %
          Shrink-swell index (Iss) ≤1 %
          Maximum particle size ≤ 100 mm

Following stripping of topsoil and any organic laden surface soils, fill must be ‘benched’ into the natural soil,
with batters over filled by 0.5 m (horizontally) and then trimmed back to the well compacted material.

It is anticipated that site earthworks could generally be completed by medium size excavators (8 tonne to 10
tonne) with toothed bucket attachments. However, the ground profile indicated by the Ground Drill boreholes




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