Reference Document - OPW25 0085 (AS Published)

As indicated by toothed bucket very slow digging terminations at depths of about 2.3 m and 2.7 m BGL,
low to medium strength (or stronger) sedimentary rock could be expected in deeper excavations.
Excavations into any low to medium strength (or stronger) sedimentary rock would likely require the use
of ripper and/or hydraulic rock breaking attachments with large equipment (e.g. 20 to 40 tonne
excavator(s)), particularly in any confined excavations (e.g. service trenching). If high strength (or
stronger) rock requires excavation, other specialised excavation methods (e.g. pre-splitting the rock using
expansive grout etc.) may be required.
Should vibratory excavation techniques be adopted (e.g. rock hammering), ground vibrations should be
monitored, and excavation methods may need to be altered should adverse impacts be anticipated or
encountered on neighbouring structures.
Should groundwater seepage be encountered during construction, such seepage should be readily
removable using gravity drainage at a low point in the excavation.

6.2.3        Batter Slopes
Unsurcharged cut batters to a maximum of 2 m deep may be temporarily formed at 1V:1H in
stiff/medium dense (or stronger) residual soils and very low strength sedimentary rock, provided
groundwater is not encountered. Steeper temporary batters may be permissible in low strength (or
stronger) rock 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 medium dense/stiff (or stronger) natural soils and very low strength sedimentary
rock up to 2 m deep may be formed at 1V:2H. Steeper and higher batters may be permissible in low
strength (or stronger) weathered rock subject to an assessment during construction. Permanent batters
up to 1.5 m high in future controlled fill on slopes <20° may be formed no steeper than 1V:2.5H.
Fissured clays were noted in the test pits and so it is recommended that a geotechnical RPEQ inspect all
batters at the time of construction.
Permanent batter slopes will require some form of erosion protection such as revegetation by
landscaping (e.g. topsoil, Jute matting and planting).

6.2.4        Filling
Future Building Works must consider the limitations on earthworks given in Section 6.1 above.
The site 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.). The weathered rock could
be used as structural fill provided the materials can be broken down to suitable particle sizes
(<100 mm).
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 75% of the Density Index for cohesionless fills (e.g. sands) or a dry density



Geo-Environmental Investigation for Proposed Subdivision
7 February 2025 | 24386-001-Rev0                                                                                  18