OPW052025 Report - Part 2

CBR testing returned a value of 1.5 % on the residual soils associated with Kin Kin Beds, which will form
the majority of the driveway alignment. A relatively high swell value (within the context of the CBR test)
of 5 % was recorded. It should be noted that the sample tested was of high silt and clay content and was
located close to the contact with the basalt ‘cap’ to the north-western corner of the lot.
The residual soils of the Kin Kin Beds elsewhere had a much higher gravel content and/or were closer to
the underlying transition to XW material and weathered phyllite. Nonetheless, the materials are expected
to be susceptible to strength loss if they become wet. Further discussion on subgrade preparation and
design CBR values in the range of materials present at this site is given in Section 6.5.


4.4           Surface Drainage
As discussed above, the topographical high point along the western/south-western boundary creates a
drainage divide and protection against waters entering the site from that direction. The ridgeline running
through the site from west to east also broadly divides the lot into a northern and southern catchment
regime.
The proposed house site has a negligible catchment for surface water being on an isolated, and high
knob within the allotment. The ridgeline upon which the driveway is proposed is rounded, and relatively
narrow, with fall away from the alignment to both sides. The catchment for the driveway would generally
be from higher parts of the ridgeline above. However, the shape of the ridgeline, being rounded, would
generally tend to spread rather than concentrate flows.
Where the driveway alignment is sidelong across the upper parts of the ridge flank to the west (Ref. Text
Figure 3), the crest is situated about 3 m above the track. A relatively steep drainage line head was
located immediately downslope of this area to the north, which would potentially be sensitive to
scouring from uncontrolled surface water flows.


4.5           Vegetation
The overall allotment consists of a mixture of cleared ground, with occasional trees extending over the
central and northern facing areas of the site. To the south-western corner, more dense bushland was
observed, including large mature trees.
No trees were present along the alignment of the proposed driveway, with the surface being maintained
by grazing and periodic sashing. Areas along the immediate edge occasionally included shrubs and vines
with sporadic, isolated copses of small trees. Widely spaced, mature trees were present on the crest of
the knob to the north-west, >10 m south of the proposed residence. Trees close to the proposed
construction areas were relatively ‘plumb,’ however some larger trees in the dense bushland away from
the construction areas were variably leaning. Where trees are leaning, this can be (but not necessarily
always) a sign of some form of instability.


4.6           Buildings & Other Structures
Towards the north-eastern frontage of the site a mixture of older and newer sheds were present. The old
shed consisted of a concrete slab, and clad structure above, and was in a dilapidated condition. A
relatively recently constructed three bay shed was located to the south-west of the older shed. The new
shed consisted of steel portal framing, sheetmetal walls and roof and a concrete ground slab.




Geotechnical Investigation & Slope Stability Assessment
9 April 2025 | 25050-001-Rev0                                                                             11