ECM_22343520_v1_Geotechnical Investigation

                                          PROPOSED RENOVATIONS
                                          2 ARAKOON CRESCENT, SUNSHINE BEACH

            Our analysis indicates that stability of the site hinges on the temporary and permanent retention systems.
            Provided that footings for the residence and structural walls are founded at least 1 m into medium dense (or
            denser) sands and the existing timber sleeper wall to the east of the residence is replaced with a new
            engineer designed and certified structure founded on shear piles, the required minimum FOS for long-term
            stability (i.e. 1.5) could be achieved.
            Our limit equilibrium modelling indicates that relatively conventional building piles could be adopted for the
            proposed development generally; however, piles socketed at least 1 m into medium dense (or denser) sand
            designed with an unfactored shear force resistance of 100 kN/m (or equivalent) will be required beneath the
            new retaining wall to the east of the residence. It should be noted that required shear and bending
            resistance of the piles and their depth should be determined by finite element analyses based on all relevant
            loads including from structures (not included in our Slope/W modelling) and all soil, fill and landscaping
            loads. To facilitate a larger level garden/grassed area to the east of the residence, the new retaining wall
            could be located further eastwards, however not beyond the current dune crest.

            The following additional recommendations are provided for the proposed development:
                     The residence and any ancillary structures (including retaining walls and pools) must be supported
                      by footings founded at least 1 m into medium dense (or denser) natural sands. Based on the results
                      of the investigation founding depths are anticipated to range between about 4 m and 5 m BGL
                      (existing ground levels). In some areas of deeper cut, high level footings may be adopted.
                      Elsewhere, piles would be required. Subsurface conditions should be confirmed by deeper borehole
                      drilling in the western part of the site following demolition of the existing structures.
                     Excavations close to site boundaries may necessitate the installation of temporary shoring prior to
                      excavation. Based upon our experience with similar projects in proximity, shoring could comprise
                      sheet piles or contiguous piles.
                     Surcharge loads across the high dune crest (i.e. east of the residence) should be limited to no more
                      than 5 kPa, unless assessed and approved by Tectonic.
                     Ground vibrations during construction should be minimised and monitored. Where excessive
                      vibrations occur, alterations to construction techniques may be required. It is recommended that a
                      dilapidation survey of adjoining structures be completed prior to construction.
                     Revegetation of bare slopes around the development area should be undertaken as soon as
                      possible following construction. Similarly, improvements to the vegetation (i.e. with endemic native
                      species) on the natural high dune face downslope of the residence would also aid in restricting the
                      development of initial surficial failures.
                     All collected roof water should be directed by pipes to the council stormwater system along The
                      Esplanade (e.g. through the use of a ‘wet’ or ‘charged’ drainage system) or, where not physically
                      possible, surface water should be directed to infiltrate into the ground around the edges of hard
                      surfaces. Infiltration areas should be set back as far as possible from the crest of the dune slope.
                      Hydraulic design should be such that under no circumstances are uncontrolled stormwater flows
                      permitted over the dune face; where channelised erosion and scour features could develop.
                     The scour in the south-eastern corner of the site should be reinstated with a cellular confinement
                      system and rock fill (gabions, reno mattress or similar) designed by a civil RPEQ.
            Based on the findings of our assessment it is considered that a Low Risk of slope instability could be
            achieved for the proposed development, subject to the following:

                     Implementation of the recommendations given in this report in preparing the preliminary design;
                     Review of the preliminary detailed design by Tectonic to confirm compliance with the
                      recommendations herein; and
                     Installing a new engineer designed and certified retaining structure supported on piles founded at
                      least 1 m into medium dense (or denser) sand, designed to accommodate an unfactored shear
                      resistance of 100 kN/m, along the eastern edge of the level area to the east of the residence.




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