J001783-001-R-Rev1

Ashley and Caroline Hermes


7.1.4 Batter Slopes
Any disturbance to natural slopes greater than about 25 degrees are not recommended, and existing slopes
on the site should not be steepened due to the potential for slope instability.
Cut batters must be inspected by a geotechnical RPEQ at the commencement of excavation, to assess
slope stability.
For short-term construction periods, excavated unsurcharged faces could be battered at 1V:1H in the natural
stiff (or stiffer) clay soils and weathered rock. Shoring will be required to enable personnel entry into near
vertical sided trenches deeper than 1 m.
Flatter batters may be required if significant groundwater seepage is encountered or if exposed faces are not
protected from erosion by rainfall.
Permanent batters should not be steeper than 1V:2H to 1V:3H in the natural stiff (or stiffer) clays. Batters
that are to be revegetated with lawn should be 1V:4H or less for maintenance (e.g. mowing). Batters in
extremely weathered (or fresher) rock may be constructed at 1V:1H.
Positive support by engineer-designed retaining structures will be required where space restrictions prevent
trimming of batters to safe slopes and where slopes are surcharged or near movement sensitive structures.
Batters must be protected from erosion (e.g. through revegetation or hard surfacing).

7.1.5 Soil Dispersion & Erosion Protection
Any excavations or disturbance of soil should be carefully monitored and managed during the construction
phase to minimise potential for scour/erosion and sediment run off.
Exposed soil (i.e. on batters or drains etc.) must be protected from erosion by appropriate measures such as
re-vegetation and hydro-seeding, protective matting, geotextiles or hard facings. Temporary sediment control
should be adopted during construction where surface water will flow offsite. Concentrating surface runoff
should be avoided unless adequate erosion protection and flow dissipation is constructed.
Erosion can lead to or exacerbate slope instability, and must be carefully managed/avoided on this site.

7.1.6 Filling and Compaction
Fill should be ‘benched’ into slopes following the above site preparation. Fill should be compacted at
moisture contents within the range of -/+ 2% of optimum moisture content for Standard Compaction.
Confirmatory testing must be carried out at regular intervals. A minimum of two tests per 300 mm vertical
interval 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. Select fill should have a maximum particle size
of 75 mm for an uncompacted layer thickness of 200 mm and shall be compacted by repeated rolling to
achieve a dry density ratio of at least 95% of the Maximum Standard Dry Density for cohesive soils, or 70%
Dry Density Index for cohesionless soils.
In accordance with good construction practice, fill embankments should be ‘over built’ and then trimmed
back to the well compacted material. Fill embankments that exceed 1 m in vertical height should be retained
using engineer designed retaining structures (refer Section 7.2) if the batter slopes recommended in Section
7.1.4 cannot be achieved.

  7.2 Retaining Structures
It is recommended that the proposed upper tier retaining wall is moved further upslope to avoid interaction
with the lower tier retaining wall, and to remove proposed steepening of the natural slope.
Retaining walls must be founded as described in Section 7.4, and designed by a structural RPEQ (including
global stability analyses).
Design for retaining structures could be carried out using a triangular pressure distribution applicable to the
wall type and based on the parameters listed in Table 3. The values in Table 3 assume that the walls are



J001783-001-R-Rev1