slope stability · MCU22/0172

Integra Partnerships                                                                           22339-001-Rev0
                                                                                            13 September 2022

It would be prudent to conduct a dilapidation survey of neighbouring structures prior to commencement of
construction.

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 minimum 4 tonne vibrating smooth drum roller or vibrating plate) to achieve required
compaction.
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 fill and 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, and at 1V:1.5H in medium dense (or denser) sand, for batters up to
3 m in height. Although unlikely, if groundwater seepage is encountered or if sloughing of dry sand occurs at
the batter surface, flatter batters or temporary retention may be required. Deeper cuts, if required, should be
specifically assessed by Tectonic.
Permanent batters up to 1 m high (vertical height) may be battered no steeper than 1V:2.5H. 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 would
be required (e.g. sheet piles, contiguous pile wall etc.). Excavations in close proximity to existing structures
and infrastructure, including on neighbouring properties, will need to be specifically designed to prevent
undermining.
It is recommended that footing exposures or confirmation of existing foundations via certified building plans
be undertaken to assess the possibility of undermining. If undermining is a potential issue the existing
structures may need to be underpinned or excavations 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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