Reference Documents - MCU23 0070

Cambooya Pty Ltd

Drainage material behind the wall should be installed for the full height of the wall, for a width of at least
0.3 m. The material must be free draining and granular and have a perforated or slotted drainage pipe at the
heel of the wall to rapidly remove the water into the stormwater system. Alternatively, the wall will need to be
designed for the full hydrostatic pressure.

6.4     Drainage & Erosion Control
Site drainage should be designed to readily remove surface water and to prevent ponding of water.
Stormwater should be piped to an engineer-designed dissipation system. Concentrated surface water flows
(e.g., roof runoff) should be avoided.

7.0       STABILITY RISK ASSESSMENT
A qualitative slope stability risk assessment for the proposed structure has been carried out following the
AGS 2007 guidelines. The risk assessment relates to property. Relative levels of risk and their implications
are given in Table 2 below and the qualitative terminology (i.e., likelihood and consequence definitions) for
use in assessing risk to property are attached in Appendix C.
Table 2: Stability Risk Levels.
 Risk Level                     Example Implications(1)

                                    Unacceptable without treatment. Extensive detailed investigation and research,
                 VERY HIGH          planning and implementation of treatment options essential to reduce risk to
 VH
                 RISK               Low; may be too expensive and not practical. Work likely to cost more than
                                    value of property.
                                    Unacceptable without treatment. Detailed investigation, planning and
 H               HIGH RISK          implementation of treatment options required to reduce risk to Low. Work would
                                    cost a substantial sum in relation to the value of the property.
                                    May be tolerated in certain circumstances (subject to regulators’ approval) but
                 MODERATE           requires investigation, planning and implementation of treatment options to
 M
                 RISK               reduce risk to Low. Treatment options to reduce to Low risk should be
                                    implemented as soon as practicable.
 L               LOW RISK           Usually acceptable to regulators. Where treatment has been required to reduce
                                    the risk to this level, ongoing maintenance required.
                 VERY LOW
 VL                                 Acceptable. Manage by normal slope maintenance procedures.
                 RISK
Note: (1) The implications for a particular situation are to be determined by all parties to the risk assessment and may depend on the
nature of the property at risk; these are only given as a general guide.

Table 3: Qualitative Risk Assessment for Property (Based on AGS 2007).
                                                                 Assessed
          Hazard             Likelihood      Consequence                                           Comments
                                                                   Risk
                                                                                Shallow translational failure in the loose sands
      Shallow failure of                                                        is considered Rare, and if the
       soils above the                                                          recommendations in this report are
                                Rare         Insignificant       Very Low
     footing zone (< 2m                                                         implemented, the consequence to property is
            depth)                                                              assessed as Insignificant. The resulting
                                                                                assessed risk is Very Low.
                                                                                The likelihood of a deep failure through the
        Deeper failure                                                          dense (or denser) sand is assessed as Rare
     through soils below        Rare             Major              Low         based on the slope profile. Although the
        footing depth                                                           consequence of such a failure would likely be
                                                                                Major, the resultant risk is Low.
 Refer Appendix C, Qualitative Risk Analysis Matrix (Australian Geomechanics Vol 42 No 1 March 2007).

Subject to the implementation of the recommendations in this report, it is our opinion that there is a Very Low
to Low Risk of global instability of the remediated retaining structure assessed in accordance with the AGS
guidelines (March 2007).




J001873-001-R-Rev1                                                                                                      Page 8