Attachment 3 - Revised Slope Stability Assessment

Brett Hage                                                                                               22328-001-Rev1
                                                                                                       17 November 2022

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 layout plans (Ref. Section 2) were available for review at the time of this assessment, however
no bulk earthworks or building design details were available regarding the proposed residence, and would be
subject to review and possibly site specific investigation and assessment prior to construction. We
understand that future building works would be located proximal to the area indicated in Text Figure 2 (not
including areas for effluent disposal).

The general building location denoted in Text Figure 2 on the future subdivided allotment is considered
suitable from a slope stability viewpoint, although it is recommended that the building envelope is truncated
such that it remains on the rounded spur running through the centre of the building area. This is shown
indicatively in Text Figure 10 below.




                                                  Building envelope on northern
                                                  side of this line only



                                             Approx. ≥12 m from boundary




Text Figure 10: Indicative restrictions on building area (base plan courtesy NC Interactive Mapping)

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 (original natural ground). All existing fill should be
removed within the proposed building areas prior to construction, and cut-off drainage installed upslope (Ref.
Sections 4.2 and 4.6, respectively). The cross-overs are expected to be generally at-grade with the existing
ground (running adjacent to the slope contours); however any future internal driveways on proposed Lot 2
should also be constructed as per the earthworks and drainage recommendations given in this report.

4.2    Earthworks
In construction areas, all vegetation, tree stumps and large roots must be ‘grubbed out’, existing uncontrolled
fill (e.g. existing earthworks pad) with any organic rich topsoil stripped from the site. It is not expected that
the horticultural fill terraces to the south-east would be disturbed. 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.




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