4895-Geotech Assessment

Mr Max Richardson                                                                                20362-001-Rev0
C/- Long View Consulting Engineers Pty Ltd                                                          28 July 2021

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 designs for the house and driveway.

4.1       Site Layout and Geotechnical Constraints
The proposed house location and driveway alignment described in Section 1.1 is considered acceptable
from a slope stability viewpoint. 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 the magnitudes
described in Section 1.1.

Any proposed fill on slopes exceeding 10° (18%) shall be fully supported by an RPEQ engineer designed
and certified retaining wall.

4.2       Earthworks
Any organic rich topsoil must be stripped from the construction areas and set aside for reuse across finished
surfaces (not to be reused in controlled fills). It is recommended that the 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 over-excavated 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 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. 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
It is anticipated that site earthworks could generally be completed by medium size excavators (10 tonne to
20 tonne) with toothed bucket attachments. However, strong phyllite could be expected within 1 m of the
ground surface. Such materials may require the use of ripping attachments, or hydraulic breaking.

Temporary batters in natural soils of stiffer (or stiffer) consistency, and future controlled fill may be formed at
1V:1H; with permanent batters formed no steeper than 1V:2H up to a maximum of 2 m in height. Near
vertical temporary batters up to 2 m high would be permissible in very low strength (or stronger) phyllite, with
permanent batters to be no steeper than 1V:1H. Flatter batters may be required if groundwater seepage is
encountered. Permanent batters will require erosion protection such as covering with topsoil, mulch, erosion
matting (e.g. Jute mat) and vegetation. Where spatial constraints prevent adoption of the above
recommended batter slopes, cut or fill batters would need to be supported by retaining walls.

The above recommendations do not supersede any existing safety regulations or legislation applicable to
excavations (e.g. limits on personnel entry into trenches).
Any excavations required adjacent to existing structures, will need to be specifically designed to ensure that
the structures are not adversely affected (e.g. 'undermined').




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