SCG 0599 - Landslide Risk Assesment

    Measure of                     INSIGNIFICANT   INSIGNIFICANT           MAJOR                 CATASTROPHIC
    consequence                              5           5                     2                             1
    RISK LEVEL                        VERY LOW      VERY LOW             VERY LOW                         LOW
                                             VL         VL                    VL                             L
The small and large rotational failures through the loose sands of very low and low risk, respectively and are
unlikely to impact the property and people who live or spend time in the area, provided the following
recommendation are adhered too:

»     All temporary and permanent retaining walls and excavations shall be design in accordance with AS4678,
      and stability analysis be carried out by a geotechnical engineering ensuring minimum Factors of Safety
      (FOS) for temporary and permanent conditions of 1.3 and 1.5, respectively are achieved.
»     All foundations of the house to be extended to the medium dense sand, as a minimum.
»     The development shall adhere to good hill side practice. Examples of good and poor hill side practice for
      the construction of residential dwelling on slopes is presented in Appendix D, Practice Note Guidelines for
      landslide risk management 2007, from Australian Geomechanics Journal Vo 42, No. 1 dated March 2007.

Excavations up to 3.0 m depth could generally be designed with a safe 1.5H:1V temporary batter slope or
2H:1V for permanent batter slopes. This assumes that soils are not wet/saturated and groundwater is not
present, and is subject to the below recommendations:

»     All temporary batters should not have construction loads (i.e. plant, equipment or soil stockpiles) or
      people at the crest of the batters at a distance equal to the height of the slope,
»     Batters should be assessed to not effect neighbouring properties/dwellings,
»     Permanent batters (at a minimum) should be protected from erosion. Topsoiling and planting, or erosion
      matting should be applied to the batter as soon as possible,
»     Suitable drainage and stormwater provisions must be installed for the batters. Surface and stormwater
      runover must be directed away from batters and prevented from pooling at the base and crest. At a
      minimum, spoon drained should be installed at the crest and base of permanent batters,
»     Temporary batters should not remain open for extended periods of time.
»     Any batters or excavations exceeding this should be inspected by a suitably qualified geotechnical
      engineer to assess to the stability of the batter, and
»     Batters exceeding the heights or slopes stated above, or batters that contain buildings or surcharge loads
      within a distance equal to one batter height from the crest, should undergo detailed stability analysis to
      determine risk levels.
If temporary batters steeper than 1.5H:1V are proposed for the site these will require the design of a suitable
retention system.

We trust this information is satisfactory for your current needs. Should you have any questions, please feel
free to contact the undersigned.

Regards,

 PTG Consulting                                                                                        Reviewed By




 Luke Goodluck                                                                                          Justin Taing
 Branch Lead – Sunshine Coast Geotechnical                                   Regional Director – Geotechnical (RPEQ 30087)
 p | 07 5647 0457                                                                                         p | 07 5647 0411
 e | [email protected]                                              e | [email protected]




SCG Consulting Engineers                            Page 5 of 5                 SCG 0599          24 September 2025