ECM_22343520_v1_Geotechnical Investigation · 132000.200173.1

                                           PROPOSED RENOVATIONS
                                           2 ARAKOON CRESCENT, SUNSHINE BEACH

            4.4         Subsurface Conditions
            The ASI investigation comprised two boreholes (designated BH1 and BH2) along the eastern edge of the
            existing residence. These boreholes encountered consistent subsurface conditions, summarised as
            follows:

                     Fill – comprising loose gravelly sand and silty sand, with deleterious materials (i.e. rubbish) from
                      the ground surface to depths between 0.9 m and 2.1 m below ground level (BGL); then
                     Natural Sand – comprising loose silty sand to the borehole termination depths of 3 m BGL.

            ASI continued DCP testing below the borehole termination depths which indicated that the natural sands
            became medium dense below depths between 3 m and 3.6 m BGL to the DCP termination depths.

            Standalone DCP testing by Tectonic along the high dune face and near the dune toe indicated the
            following:

                     Very loose/loose sands to depths between 1.1 m and 2.3 m BGL; then
                     Medium dense sands to depths between 1.4 m and 4 m BGL; followed by
                     Dense to very dense sands with practical DCP refusal at depths between 1.6 m and 5.8 m BGL.

            4.5         Groundwater
            No signs of groundwater seepage (‘springs’) were observed at the ground surface during our walk-over. No
            groundwater was mentioned on the ASI borehole reports, with the soils described as ‘moist’.

            Groundwater conditions are expected to be reflective of prevailing weather conditions and seepage may
            develop, particularly following periods of prolonged or heavy rainfall at various points 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         Surface Drainage
            Surface drainage would be expected to follow natural surface gradients to the east towards the beach. The
            site has a relatively small catchment, with some run-off expected to enter the site from upslope along The
            Esplanade; however, most of which should be intercepted by the existing kerb along the frontage.

            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.

            A scour was observed in the south-eastern corner of the site, downslope of the existing residence. The
            scour was estimated to be between 1 m and 2 m deep with side scarps dipping between 40° and 50°. A
            coir log ‘silt sausage’ was observed above the head of the scour feature which was bulging with debris. A
            PVC outlet was also observed upslope of the area which discharged directly onto the ground surface, with a
            corresponding scour about 0.5 m deep. It appeared that concentrated stormwater runoff discharged into
            this area, resulting in the observed scour features.

            Anecdotal evidence by the owner suggests that stormwater previously discharged into the area including
            from the road surface above, with works undertaken to attempt to divert the water away from the area.
            Stormwater improvements are recommended in Section 6.4.

            No other significant surface run-off features were noted across the allotment during our assessment.




             24 February 2023
             Report No. 22484-001-Rev0                               8
Document Set ID: 22343520
Version: 1, Version Date: 16/03/2023