Approved Plan - EXE21-0015

Mr Dean Frith                                                                                    21182-001-Rev0
                                                                                                    28 May 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 design for the shed at the site.

4.1     Site Layout and Geotechnical Constraints
The proposed shed location 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.

4.2     Key Mitigation Measures
Recent instability has occurred in the fill embankment to the north. The following mitigation measures are
recommended from a geotechnical viewpoint to achieve a Low Risk of slope instability the shed from the
existing earthworks. It should be noted that this risk assessment excludes geotechnical risk that may be
associated with settlement due to consolidation of the uncontrolled fill material over time which could affect
non-piled structures (e.g. driveways, landscaping structures).
      1. The shed must be setback at least 1 m from the crest of the fill embankment.

      2. The fill embankment will need to be trimmed back to well compacted materials (to the lines of
         tension cracking) and flattened to a maximum grade of 1V:2.5H, or otherwise supported by an
         engineer designed and certified retaining wall.

      3. All batters should be protected from erosion by surface protection, the type of which will be
         dependent upon a number of factors including batter slope, material type, aspect, aesthetic finish
         required, etc. As a minimum, all soil batters should be topsoiled and seeded (or hydromulched) to
         establish a permanent grass (or similar vegetation) cover.

      4. As the existing fill platform is deemed to be uncontrolled, it is possible that unsuitable fill materials
         may be present within the fill. Therefore, to minimise future settlement due to consolidation of this fill
         it is recommended that the platform subgrade should be proof rolled using a fully laden water cart (or
         similar heavy onsite equipment) to identify any ‘soft spots’. Any such soft spots should be excavated
         and replaced with select fill material. Tree stumps and large roots must be ‘grubbed out’.

      5. Ongoing consolidation settlement of the fill is expected to occur over the long term as the particles
         realign to find an equilibrium position. Given the uncontrolled nature of the fill, settlement might be
         expected to be in the order of 1%H up to 2%H, where H is the height of fill. Differential settlements
         across the building pad from the cut to fill areas should be expected and accounted for in the design
         of adjacent surface or in ground elements (e.g. driveway slab and underground services).

      6. Diversion drainage must be installed above the crest of any cut/fill embankments to divert
         stormwater away. All stormwater must be directed by pipes or lined channels to discharge at least
         10 m downslope from any structure or embankment and not upslope of any neighbouring
         structures/embankments.


Subject to the above rehabilitation earthworks, and relatively conventional hillside construction practices
such as ensuring all footings for the proposed shed and ancillary structures (e.g. retaining walls) penetrate
through any fill and natural soils to found into underlying weathered rock, limiting future fill earthworks and
formalising onsite drainage, it is assessed that a Low Risk of instability affecting the proposed shed could be
achieved.
Specific recommendations relating to the above key measures and earthworks, footing design, retaining
walls and drainage are outlined in the sections below.




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