Attachment C - Soil Survey Report · MCU18/0013

Project No. 1-20119                                                                                                        Page | 11
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach




TABLE 2                LIKELIHOOD RATING
          MacGregor and Taylor (2001)                                   Landslide Risk Management (2007c) Appendix C
                                                                                                   Adopted Indicative
 Relative Frequency                  Likelihood Rating                  Likelihood Descriptor       Value of Annual
                                                                                                       Probability
                                                                                                             -6
           < 0.2                           Very Low                         Barely Credible                10
                                                                                                         -5     -4
         0.2 to 0.6                          Low                            Rare to Unlikely           10 to 10
                                                                                                         -4     -3
         0.6 to 2.0                        Moderate                       Unlikely to Possible         10 to 10
                                                                                                         -3     -2
         2.0 to 6.0                          High                          Possible to Likely          10 to 10
                                                                                                             -1
           > 6.0                           Very High                        Almost Certain                 10
Note: 1. McGregor & Taylor (2001).
      2. Likelihood adopted based on Landslide Risk Management (2007c), Appendix C.

           5.4.3       Hazard A - Natural Shallow Landslide

The site was assessed using the parameters as described by MacGregor and Taylor (2001)
and the site features identified on the supplied information, observations made whilst on site
and where necessary worst case parameters.

Therefore, based on this assessment, natural shallow landslides on the site have been given
a likelihood hazard rating of Very Low for Area Ia and Low to Moderate for Area Ib (moderate
rating relates to eastern boundary slopes). These ratings translate to a Likelihood Descriptor of
Barely Credible for Area Ia and Unlikely for Area Ib.

           5.4.4       Hazard B - Proposed Cuts

Cuts are understood to be proposed within the site for the ground and first level floors. Given
the adjacent structures, these cuts are expected to abut parts of the northern, southern and
western boundaries. We understand from original drawings of the site to the north (dating back
to 2006) that the existing residence has a basement at approx. RL 20.0m for the full length of
adjoining boundary.

The existing sheet piles understood to be installed on the site are proposed to be utilised to
partly support the internal cuts, with areas of new sheet piles also to be installed along the
southern boundary and to extend the western boundary.

Given the above, we understand that all cuts will be supported temporary during construction by
sheet pile walls then permanently by construction of other retaining structures. To assess these
cuts, the method outlined by MacGregor & Taylor (2001) for the assessment of cuts has been
adopted. No batters are understood to be adopted for excavations.

The assessment has taken into account the proposed wall geometry (based on provided
drawings and site measurements), expected subsurface profile (from site investigation) and
proposed development (based on provided drawings).

Information in relation to the design parameters or structural elements of the wall is not
available at this stage. Therefore, the assessment has also assumed that all retaining walls
(both temporary and permanent) will be adequately engineer (RPEQ) designed and certified.

Assuming all cuts are adequately supported by retaining structures and that no evidence of
instability is noted in the cuts once completed, then a likelihood hazard rating of Low to
Moderate would apply to the temporary cuts. This translates to a Likelihood Descriptor of
Unlikely.