Att 3 - Landslide Risk Assessment

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Existing Dwelling
There is an existing dwelling on this site which, when removed, will cause some disturbance to the
strata down to depths equal to the depth of the footing. We have assumed that either this disturbance
will be back-compacted so the performance of the proposed footings is not compromised or piered
through. If during the earthworks phase it is apparent that the disturbed ground is proving
problematic, then the design engineer must be consulted to reconsider the situation.
Furthermore, there are generally several uncharted abandoned sub-surface pipes, which generally
hold a limited amount of water both within themselves and in the sand bed around them. If footing
excavations encounter any of these pipes some local seepage may occur, but normally a
competent contractor can cope with this situation.
Low Bearing Capacity
Testing indicates that layers of the observed strata have low bearing capacity between 50 and
100kPa. Whist these layers may be suitable for slab on ground construction as per AS2870, these
layers may not be suitable to supporting isolated footings without specific engineering design.
Slope Stability
There are some areas nearby which the local authority may believe to be subject to landslip.
Although our commission has specifically excluded consideration of landslip, this does not exclude
the possibility that the local authority may request a Slope Stability Assessment for this project, nor
does it exclude the possibility that during estate development modifications to the site may have
masked any indicators of previous instability.
We do not see any reason why construction should not proceed in accordance with the above
classification, but if during the various stages of development the possibility of slope instability is
flagged by the certifying authority, then a more detailed investigation may be required. In this
circumstance, we reserve the right to revise or withdraw this report without penalty. In some cases a
slope stability assessment report already exists, but its importance may not have been recognised
and not forwarded onto us. If required, we can provide a quotation for a slope stability report or
appraise any existing report.
Water Table
Although no water table was encountered during our testing, a perched water table or water seepage
can occur during or after wet periods, generally where a porous layer overlies less porous strata.
This generally results in some water seepage into excavations down to this level, but a competent
contractor can usually resolve this issue.
Other Considerations
Prior to construction, our classification assumes all topsoil/estate dressing and any debris including
organic vegetation is stripped clear from the building platform. Providing the exposed surface after
site clearing is proof rolled and any new fill is compacted and certified in accordance with AS3798-
2007 as “controlled” fill, then we do not see the need for additional fill piers on this site, other already
mentioned above. Service piers maybe required for structural footings which maybe within the zone
of influence of retaining walls, underground services, pools, inground tanks etc.




AWT 77775 Site Classification Report
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