Reference Document - MCU25 0060 (As Published)

Table 3: Details of Qualitative Risk Assessment for Property (AGS 2007)
                                                             Assessed
 Hazard                           Likelihood   Consequence
                                                             Risk
                                                                        Comments
 Failure through very loose to    Unlikely     Medium        Low        Given the moderate natural gradients through the
 loose natural sands above the                                          proposed building area and limited depth of loose or
 foundation depth                                                       very loose sands, it is considered Unlikely that a landslip
                                                                        would develop in these materials, subject to
                                                                        implementation of the recommendations in Section 4.
                                                                        Given a potential Medium impact from such instability
                                                                        the resultant risk would be Low as per AGS 2007.

 Deep failure through the         Rare         Major         Low        The likelihood of a deep failure through the medium
 medium dense (or denser)                                               dense (or denser) natural sand below the proposed
 sands below the foundation                                             foundation depth is assessed as Rare due to the lack of
 depth                                                                  precedence of such movements locally, no signs of any
                                                                        existing slope instability and a lack of groundwater.
                                                                        Although the consequence of such a failure would be
                                                                        Major, the resultant risk is Low as per AGS 2007.

 Temporary instability through    Rare         Major         Low        The likelihood of a slide/failure through any temporary
 temporary retention system, as                                         retention system (sheet pile wall, contiguous pile wall or
 discussed in Section 6.4.                                              similar) as outlined in Section 6.4, is assessed as Rare,
                                                                        subject to detailed design by a suitable qualified RPEQ
                                                                        engineer and construction by a specialist contractor
                                                                        which accounts for the required factors of safety against
                                                                        slope instability. Although the consequence of such a
                                                                        failure would be Major, the resultant risk is Low as per
                                                                        AGS2007.



The potential impacts on slope stability of the development components have been assessed, and the
measures recommended below in Section 4 have been designed to mitigate those impacts.

5.2.1          Quantitative Assessment
In order to estimate the factor of safety (FOS) against slope instability for the proposed development,
numerical analysis has been conducted using Slope/W including consideration of groundwater
conditions. As per the advice in the recommendations below, it is expected that footings would be taken
to found in the underlying medium dense (or denser) sands, and therefore a surcharge on the subgrade
would only occur where these materials are expected to daylight following bulk excavation. A surcharge
load of 10 kPa per residential storey has been adopted in these locations. A 5 kPa uniform surface has
been applied in all proposed external landscaped areas otherwise. Groundwater levels were assumed at
2 m BGL, which is noted to be conservative, given the sandy subsurface profile and the ground
conditions encountered during our investigation.
The approximate extent of the section line analysed as part of numerical analysis (Section A-A’) is
indicated in Figure 1. The key points from our analyses for the proposed development are summarised as
follows (given overleaf):




Proposed Residential Development
25 August 2025 | 25038-001-Rev0                                                                                                       11