271117 Techtonic GeoTech Cooroy Mtn Rd

Mr Ken Freeman                                                                                    17385-001-Rev0
                                                                                                27 November 2017

5.0        COMMENTS AND RECOMMENDATIONS
General recommendations to help maintain the stability of the site are given in the document “Some
Guidelines for Hillside Construction”, which is attached.

5.1       Building Locations
As indicated by concept drawings provided by the client, we understand that the largest potential structures
(possible future extension) will be located to the east side of the house, with smaller elements to the west,
south, and south-east. Should the proposed construction areas be amended, Tectonic must review this
stability assessment.

5.2       Earthworks
Based on provided information including a concept layout plan, survey drawing and discussions with the
client, the following cut/fill operations are anticipated:

          Car port: a small cut in residual material is already present, approximately 1 m high on the upslope
           side of the car port west of the house.
          Rear of existing house: filling is anticipated to be at least 2.0 m high to the north side of the house
           within and surrounding the existing pool.
          Possible future extension of residence: a cut of up to 3 m on the upslope side of the building footprint,
           and filling up to about 2.5 m (which will be retained) on the downslope side of the extension.

Tectonic must review the impacts on stability if cut/fill earthworks exceed these estimated depths/heights. All
fill batters and cuts greater than 1 m high should be retained by engineer designed and certified retaining
walls.

Following stripping of topsoil, and any organics/tree roots, the subgrade should be proof rolled using a
5 tonne roller to identify any soft/loose areas. Proof rolling in areas of cut may be deferred until after
excavation. Soft/loose areas should be over-excavated to a stiff foundation, and backfilled with compacted
fill as per the recommendations below. The stripped surfaces in fill areas should be assessed by a suitably
qualified geotechnical engineer prior to the commencement of filling.

Fill materials should be compacted at moisture contents within the range of -2% to +2% of optimum moisture
content for Standard Compaction. Confirmatory 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”. Select 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 pad foot
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.

Sloping ground must be ‘benched’ prior to placement of fill. Fill batters should be over-filled by 0.5 m
(horizontally) and then trimmed back to the well compacted material.
Rock may require ripping or breaking with pneumatic attachments in the area of the proposed future
residential extension, and the effects of vibration on adjacent structures should be taken in to account when
undertaking the work. The foundation details of the surrounding structures should be ascertained, to avoid
undermining the foundations during the excavation works. Text Figure 8 on page 12 provides guidance on
the zone of influence for footings to avoid undermining.

Temporary batter slopes should not exceed 1V:1H, and may need to be flatter if groundwater seepage is
encountered or if earthworks are carried out during a period of wet weather. The impact of surcharge loads
due to existing structures at the crest of any fill batter must also be considered during planning of
excavations.

Permanent batter slopes should be finished at a maximum grade of 1V:2H in stiff (or stiffer) natural material,
and controlled fill. If there is insufficient space to form such batters, retaining walls should be constructed.
Permanent batters will require erosion protection, e.g. revegetation or surface protection.




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