4. 220148 - Slope Stability Report (2) · 132006.2554.01

Seachange Builders                                                                              22134-001-Rev0
                                                                                                   26 April 2022

4.2.2        Filling
The existing sandy soils (excluding topsoil) may be reused as structural fill, subject to appropriate moisture
adjustment. It should be noted that compaction of such relatively ‘clean’ sands as structural fill requires the
addition of substantial volumes of water (‘flooding’) combined with the use of vibratory compaction
equipment (typically a smooth drum roller or vibrating plate).

Should importation of fill be required, it is recommended that such fill should comply with the following:

       Minimum CBR of 10%
       Maximum plasticity index of 15%
       Shrink-swell index ≤ 1%
       Maximum particle size of 100 mm
Any fill should be compacted at moisture contents within the range of ±2% of optimum moisture content for
Standard Compaction. 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 small compactor 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.

Confirmatory compaction testing should be carried out at regular intervals. A minimum of two tests per
vertical lift is recommended where structural fill heights are to exceed 300 mm. 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 embankment edges must be over-filled by 0.5 m (horizontally) and then trimmed back to well compacted
material.

4.2.3       Excavations
Excavations through the natural soils encountered in the boreholes should be achievable using conventional
earthmoving plant (e.g. small excavators). Non-surcharged temporary cuts in the very loose to loose sands
could be formed at 1V:2H, for batters up to 2 m in height. Although unlikely, if groundwater seepage is
encountered, flatter batters may be required. Deeper cuts, if required, should be specifically assessed by
Tectonic. Permanent fill batters up to 1 m high (vertical height) may be battered at no steeper than 1V:3H. All
remaining permanent cut/fill batters must be supported by engineer designed retaining walls. Any permanent
soil and fill batters will require erosion protection (e.g. revegetation or surface protection).

If the above temporary batter slopes cannot be achieved, due to spatial restraints, temporary shoring will be
required (e.g. sheet piles). Excavations in close proximity to existing structures/infrastructure will need to be
specifically designed to prevent undermining. If undermining is a potential issue the existing structures may
need to be underpinned or the excavation may require temporary shoring.

The advice of a suitably qualified and experienced structural RPEQ must be sought regarding any potential
undermining and design and construction of any underpins/temporary shoring (if required).

The above recommendations do not supersede any existing safety regulations or legislation applicable to
excavations (e.g. limits on personnel entry into trenches).

Due to the highly permeable nature of the sands at this site, stormwater is expected to rapidly infiltrate the
ground, making un-sealed surface drainage ineffective for the control of flows. Any sealed areas should be
graded to ensure free drainage of stormwater away from construction areas, and to a control point(s).




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