Reference Document - Geotech Report - MCU24 0094 · MCU24/0094

                               PROPOSED RESIDENCE
                               33 ROSS CRESCENT, SUNSHINE BEACH

4.4       Subsurface Conditions
Detailed descriptions of the subsurface conditions encountered in the boreholes are provided in the
borehole reports attached in Appendix A, along with definition sheets which describe terms and
abbreviations used on the reports. Subsurface conditions encountered in the boreholes are summarised
as below and are illustrated as a cross-section in Figure 2.

The boreholes and in situ test results indicate a subsurface profile of relatively poorly graded dune sands to
the maximum investigation depth of the borehole drilling and testing. Very loose and loose sands were
deepest in boreholes BH2 and BH3, at the dune crest, extending to about 2.7 m BGL.

Table 1 below provides a more detailed summary the subsurface profile encountered in each borehole
(noted in a west to east direction, Ross Crescent to high foredune toe).
Table 1: Summary of Subsurface Profiles
    Material / Test
                              BH1             BH2              BH3           DCP4          DCP5           DCP6
      Location
  Very Loose to Loose                                                                     *0.0 – 1.9
                            0.0 – 1.2       0.0 – 2.7      0.0 – 2.5       *0.0 – 2.4                    *0.0 – 2.3
         Sands                                                                            *2.4 – 3.0
                            1.2 – 1.5
    Medium Dense                            2.7 – 4.0      2.5 – 3.0                      *1.9 – 2.4
                            2.0 – 4.0                                      *2.4 – 2.7                    *2.3 – 3.8
       Sands                               *4.0 – 4.6      *3.0 – 3.4                     *3.0 – 3.4
                            *4.0 - 4.8
   Dense (or denser)      1.5 – 2.0
                                        *4.6 – 5.1 TD   *3.4 – 4.4TD      *2.7 – 2.8TD   *3.4 – 3.9TD   *3.8 – 3.9TD
        Sands           *4.8 – 5.5 TD
Notes: 1.       Depths noted in m BGL at time of investigation (3 April 2024)
       2.       TD denotes DCP test termination depth

       3.       * denotes materials inferred from DCP results

4.5       Groundwater
No signs of groundwater seepage (‘springs’) were observed at the ground surface during our walk-over. It is
expected that an unconfined groundwater table would exist at the toe of the dune, close to sea level, and
fluctuate with tidal and weather conditions.

Groundwater seepage may develop, particularly following periods of prolonged or heavy rainfall at various
levels through the dune profile. Based upon experience at other similar sites in the area, such seepage
would be expected to be transient and of relatively minor lateral extent.

4.6       Geotechnical Laboratory Test Results
PSD analysis on two sand samples selected from boreholes BH1 and BH2 indicates that the soils generally
comprise poorly graded, fine to medium grained sand (predominantly medium grained). The samples tested
had a very low proportion of silt fines at 4 % and 3%, respectively (i.e. the dune sands are relatively ‘clean’).
Full test results (laboratory certificates) are presented in Appendix B.

4.7       Surface Drainage
Surface drainage would be expected to follow natural surface contours to the east towards the beach. The
site has a relatively small catchment, with the majority of upslope run-off expected to be intercepted by the
kerb and channel drainage along Ross Crescent.

Given the sandy nature of the site, rainfall would normally be anticipated to infiltrate the ground surface
relatively quickly. However, as the proposed development will occupy a large part of the block, significant
run-off from hard surfaces will likely occur. Nevertheless, where directed into swales rather than pipes,
such run-off would be expected to infiltrate into the natural sands relatively rapidly. No significant surface
run-off features were noted across the allotment during our assessment (e.g. deep rilling or scour/wash out
scars).




18 June 2024
Report No. 24096-001-Rev0                                  8