Att 3 - Landslide Risk Assessment

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Filled Ground                                                  Furthermore, there should be no in ground disposal or
Controlled Fill - Material that has been placed and            storage of water, (i.e. soakage pits, rubble pits, rain
compacted in layers by compaction equipment within a           gardens or similar), within eight (8) metres of a structural
defined moisture range to a defined density requirement in     footing, without our prior written approval.
accordance with AS 3798-2007 Clause 6.4.2 of AS 2870-          Where the proposed earthworks involve the establishment
2011 defines controlled fill.                                  of cut/fill batters, advice concerning safe angles is beyond
Uncontrolled Fill - Fill that does not have sufficient         the scope of commission in this report. AS 2870-2011,
documentation to be classified as controlled is by             Clause 6.4.4 offer guidelines.
exclusion, uncontrolled. Where found we have offered           Long Term Site Management
further advice within this report.                             It is the owner’s responsibility to ensure both tenants and
Topsoil/Estate Dressing                                        future owners are aware of these responsibilities. The
In our soil log section, where we have logged “Topsoil” or     referenced CSIRO sheets outline these responsibilities
“Estate Dressing” it is defined as per clause 1.2.15 of AS     and if the builder does not give the owner a copy, they can
3798-2007 thus:                                                be sourced from either the CSIRO (1800 645 051) or our
                                                               office.
“A poorly compacted superficial soil containing some
organic matter, usually darker than the underlying soils”      The major danger to dwellings is allowing site conditions
                                                               to deteriorate to “abnormal” in the long term.
Good building practice dictates that all heavy organic
strata be scraped clear of the building envelope during the    Where abnormal moisture conditions are allowed to
early stages of site preparation and we have assumed that      continue or to develop, then not only will the above
this will be done.                                             probabilities increase, but the damage will be greater.
Short Term Site Management                                     The CSIRO sheets define both “normal” and “abnormal”
                                                               conditions.
This is the responsibility of the builder, and besides
ensuring that the site is handed over to the owner at          The significant (not necessarily in order) abnormal
completion in accordance with accepted practice, the           conditions that adversely affect the performance of AS
following should also be done:                                 2870-2011 type footings are:
§ Ensure all service trenches are back-filled as soon as       § Trees growing or allowed to grow within the critical
     possible in accordance with Clause 6.6 of AS 2870-              zone of influence of the footings.
     2011, including the clay plug where a service pipe        § Poor site drainage
     trench exits the building footprint.                      § Saturated service trenches (poor site drainage).
§ Ensure guttering is connected to the stormwater (via         § Leaking service pipes
     temporary pipes if necessary) as soon as the roof is      The builder, owner/occupier and engineer should take
     on.                                                       note that management of trees is the most difficult part of
§ Ensure that during construction and at the time of           the site management procedures and trees present the
     hand-over that the site is maintained as per Clause       greatest risk to the future poor performance of the footing
     5.2.1 of AS 2870-2011.                                    system. Trees (existing or proposed) must not be allowed
If any of these practices are not carried out, the site may    to grow without taking action to negate their effects within
develop “abnormal” moisture conditions, increasing the         the critical zone of the footing system.
risk of damage above the AS 2870-2011 criteria.                  Class           Normal ys      Critical Zone
Other Construction Issues                                        Class M         < 41mm         .75 times mature height
The builder must also ensure that other sub-trades such          Class H1        41-60mm        1.0 times mature height
as plumbers, drainers and swimming pool contractors
                                                                 Class H2        61-75mm        1.0 times mature height
don’t establish excavations within the critical zone of
influence of the footing system unless the footing is piered     Class E         76-100mm       1.5 times mature height
below the influence of these excavations. This critical          Class E         >100mm         2 times mature height
zone varies from 20° (1V:2H) to 45° (1V:1H), depending         These spacings must be increased for groups or rows of
on the nature of the strata. If this situation is considered   trees.
possible, then once the proposal is known we can offer         These distances are only a “rule of thumb” as the tree
further advice. These excavations include inground tanks.      species and their root systems play an equally important
Unless we have specifically given written approval, no         role. Refer Appendix H and/or CH or AS2870-2011.
inground tanks should be sited within 8 metres of any
structural footing.




AWT 77775 Site Classification Report
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