Appendix D - Geotechnical Report

7.           Geotechnical Recommendations
General recommendations to help maintain the stability of the site are given in the document Some
Guidelines for Hillside Construction, which is attached in Appendix C.


7.1          Development Limitations
From a geotechnical and slope stability perspective the proposed site layout would be acceptable. To
achieve a Low Risk of slope instability (and factor of safety of 1.5 or more) the following is recommended
for future development:
▪    Unretained filling should be limited to 1 m height where ground slopes are 10° or greater, or should
     be retained. Earthworks fill greater than 1 m height could be tolerated, subject to assessment and
     approval by a geotechnical RPEQ.
▪    All retaining walls exceeding 1 m high and/or subject to surcharge loads must be engineer designed
     and certified, which must include an assessment of global and internal stability by the designer.
▪    With the relatively wide nature of the spurs present on proposed Lots 1 and 5, and in the alternative
     building envelope on proposed Lot 2, conventional low-set construction is expected to be possible.
     Given the moderately steeply sloping ground to the south-west of proposed Lot 2 and the south of
     proposed Lot 4, high-set, lightweight suspended construction may be more practical.
▪    The building envelopes identified in the project brief (Ref. Section 2) would be feasible from a
     geotechnical and slope stability perspective on each lot. As the building areas are relatively large,
     site-specific ‘soil testing’ and slope stability assessment must be undertaken for future construction
     on each allotment.


7.2          Earthworks
In construction areas, all vegetation and large roots must be ‘grubbed out,’ with any organic rich topsoil
stripped. Organic topsoil must not be reused as structural fill, however, may be reused for landscaping
purposes. Although trafficability should generally be good in ‘dry’ conditions, the soils could be subject
to strength loss from repetitive heavy 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 and
building platforms.
Excavations in the materials encountered to the test pit termination depths should be achievable using
conventional earthmoving equipment (e.g. excavators with augers and toothed buckets). Deeper
penetration (particularly in confined excavations) would require ripping attachments on possibly larger
machines for efficient excavation.
Temporary, unsurcharged batter slopes should be constructed at maximum grades of 1V:1H in stiff (or
stiffer) natural soils. Flatter batters may be required if groundwater seepage is encountered.
Permanent batter slopes in the stiff (or stiffer) natural soils may be formed at a maximum grade of 1V:2H,
and in ‘controlled fill’ at 1V:2.5H. Permanent batters will require erosion protection such as covering with
erosion matting or vegetation. Where spatial constraints prevent adoption of the above recommended
slopes, batters would need to be supported by RPEQ engineer designed retaining walls.




Geotechnical Investigation
10 June 2026 | 26073-001-Rev0                                                                             17