Geotechnical Report Dec 2013 Revision 1

                              55 LAKE MACDONALD DRIVE, COOROY


select fill or tyning, appropriate moisture adjustment and compaction. Proof rolling should be carried out in the
presence of an experienced geotechnical engineer.

The site should be graded to shed surface water runoff away from earthworks and/or construction areas. .
Appropriate erosion and sediment control measures must be installed prior to commencement of earthworks
at this site.

In addition to the above assessments, a “proof” roll was conducted using the 8 tonne excavator across the
gully area between Stages 3 and 4, near the existing concrete culvert. This area was assessed for
traffickability as it appeared to be wet and soft ground. The excavator was able to traverse this area with no
difficulties. It is expected that this area would become softer and more difficult to access following wet
weather. Although the surface conditions were dry and hard at the time of the investigation, tyre ruts about
200mm deep were noted in the area between the gully and test pit TP5 on the eastern side of the drainage
gully.

6.1.2        Excavations
Excavations for future services are expected to be in loose to medium dense clayey sand and stiff (or stiffer)
sandy/silty clays. Test pit TP10 was located in an area of a future sewer manhole, with an invert level
approximately 2.5m BGL. The subsurface profile comprised medium dense silty/clayey sand over stiff sandy
clay to 2.2m BGL (maximum depth reach of excavator). Some groundwater seepage was noted at a depth of
1.4m BGL.

Excavations in the silty/clayey sand and sandy clay materials are expected to be achievable using typical
earthmoving plant (e.g. medium to large excavators, dozers). Rock was not encountered in any of the other
test pits, which were excavated to depths of up to 1.5m BGL.

Unsurcharged excavation batters could be temporarily formed no steeper than 1V:2H in the natural soils. The
presence of groundwater seepage may necessitate flatter batters.

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

Groundwater seepage was noted to be slow, and is expected to be removable by grading excavations to a low
point and pumping water from a sump.

6.1.3        Drainage Gullies
We understand that the drainage gullies may be rehabilitated by stripping and re-grading the existing ground
surface, followed by placement of rock spalls, and erosion protection measures (jute matting, topsoil, and
mulch).

Following striping of surface vegetation, the exposed material is expected to comprise silty clay. Where this
material was noted to be wet (e.g. test pit TP8, boreholes HA1 and HA2), a significant reduction is strength
was observed (e.g. soft to firm). At test pit TP11 (located within the central gully), the silty clay underlying the
topsoil was noted to be moist and stiff. The 7 tonne excavator was also able to traverse the area adjacent to
the central drainage gully.

At boreholes HA1 and HA2, the silty clay was described as firm at about 0.5m BGL, then stiff (or stiffer) below
0.8m BGL (based on DCP test results). As discussed in Section 5.2, at HA1 and HA2, the silty clay may
actually be stiff from 0.5m BGL.

Based on the above results, it appears that stiff (or stiffer) clays are present at depths within 0.8m BGL. It is
expected that stiff (or stiffer) silty clay will form a suitable foundation for the placement of rock spalls. If time
and subsurface conditions permit, it is possible that the upper soft to firm clay recorded in HA1 and HA2 to a
depth of 0.8m BGL, could be dried, tyned and re-compacted. This will reduce the volume of material to be
stripped to provide a suitable foundation for placement of rock spalls. To achieve this, the drain will need to be
cleaned out and re-graded to maintain flow towards the outlets, to allow for the clay to dry out so that tyning
and compaction may be undertaken.




2 December 2013
Report N0. 13008-001-Rev1                               11