Appendix F - Geo-Environmental Investigation Report · RAL24/0003

                              PROPOSED SUBDIVISION
                              41 TALLOWWOOD PLACE, BLACK MOUNTAIN

6.2.3        Batter Slopes
Unsurcharged cut batters to a maximum of 2 m deep may be temporarily formed at 1V:1H in the natural
residual soils and weathered phyllite, provided groundwater is not encountered. Steeper temporary batters
may be permissible in low strength (or stronger) weathered phyllite subject to an assessment during
construction by a geotechnical RPEQ. Where space limitations occur or the above temporary batter slopes
are not achievable, installation of temporary retention would be required.

Permanent batters in very stiff (or stiffer) residual clays and very low strength (or stronger) phyllite up to 2 m
deep may be formed at 1V:2H. Steeper and higher batters may be permissible in low strength (or stronger)
phyllite subject to an assessment during construction by a geotechnical RPEQ. Permanent batters up to 1 m
high in future controlled fill on slopes <10° may be formed no steeper than 1V:2.5H. All fill on slopes
exceeding 10° must be supported by engineer designed and certified retaining structures, unless assessed
and approved by a geotechnical RPEQ. Permanent batter slopes will require some form of erosion
protection such as revegetation by landscaping (e.g. topsoil, Jute matting and planting).

Placement of heavy ‘builders plastic’ or filter ‘cloth’, pinned to batters may be required if heavy of prolonged
rainfall occurs during construction. Exposure of temporary batters should be minimised in order to limit
shrinkage cracking in clayey soils and potential development of temporary instability.

6.2.4        Filling
The high plasticity cohesive (clay/silt) soils, where free of deleterious materials (e.g. organics, oversize etc.),
could be reused as structural fill, or as non-structural fill (e.g. in landscaping areas, batters, etc.). It should
be noted that reuse of high plasticity soils may have adverse implications for pavements (low CBR values)
and future house construction (high reactivity resulting in Class H2 or higher site classification). Site won
clay/silt materials should be placed in the lower fill layers at least 0.5 m below finished platform levels, where
possible.

It should also be noted that due to the high silt content the natural soils would develop poor engineering
qualities when wet of optimum moisture content and would be difficult to handle and place during
earthworks, which should be considered during earthworks planning.

The weathered phyllite could be used as structural fill provided the materials can be broken down to suitable
particle sizes (<100 mm). Depending on the method of excavation used, re-use of any medium strength (or
stronger) weathered phyllite as structural fill may not be possible without specialised processing (e.g. use of
a mobile crushing plant).

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%
       Maximum particle size of 100 mm

All structural fill should be compacted at moisture contents within the range of ±2% of OMC for Standard
Compaction. Fill should be placed in 250 mm thick (loose thickness) layers and be compacted by repeated
rolling to achieve a dry density ratio of at least 95% of the maximum Dry Density Ratio (DDR), or 100% DDR
based upon the Standard Compaction method within 0.3 m of pavement subgrades.
Confirmatory compaction testing must 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. It is recommended that Level 1 geotechnical inspection and testing be
conducted for all Operational and Building Works filling where fill heights exceed 0.5 m.

Due to the sloping nature of the site, all fill must be ‘benched’ into the natural slope, over-filled by 0.5 m
(horizontally) and then trimmed back to the well compacted material.




22 May 2023
Report No. 23099-001-Rev0                                15