Reference Document - Geotechnical Investigation Report - DBW24/0090 & RAP24/0025

                Rebecca Stead                                                                                     20248-001-Rev0
                                                                                                                3 September 2020

                and testing of fill are given in Australian Standard AS 3798-2007 Guidelines on Earthworks for Commercial
                and Residential Developments.

                Fill embankment edges must be over-filled by 0.5 m (horizontally) and then trimmed back to well compacted
                material.

                4.2.3         Excavations
                Excavations through the existing soils should be achievable using conventional earthmoving plant (e.g. small
                to medium excavators in the 4 tonne to 12 tonne range). Unsurcharged temporary cuts in the very loose to
                loose sands could be formed at 1V:2H, for batters up to 2 m in height. If groundwater seepage is encountered,
                flatter batters may be required. Deeper cuts, if required, should be specifically assessed by Tectonic. All
                permanent cut/fill batters must be supported by engineer designed retaining walls.

                If the above temporary batter slopes cannot be achieved, due to spatial restraints, temporary shoring will be
                required. Excavations in close proximity to existing footings will need to be specifically designed to prevent
                undermining. It is recommended that footing exposures or confirmation of foundations via certified building
                plans be undertaken to assess the possibility of undermining. If undermining is a potential issue the existing
                structures may need to be underpinned or the excavation may require temporary shoring such as sheet
                piles.
                The advice of a suitably qualified and experienced RPEQ structural engineer must be sought regarding any
                potential undermining and design and construction of any underpins/temporary shoring (if required).

                The above recommendations do not supersede any existing safety regulations or legislation applicable to
                excavations (e.g. limits on personnel entry into trenches).

                Due to the highly permeable nature of the sands at this site, stormwater is expected to rapidly infiltrate the
                ground, making un-sealed surface drainage ineffective for the control of flows. Any sealed areas should be
                graded to ensure free drainage of stormwater away from construction areas, and to a control point(s).

                4.3     Footings
                Due to the very loose to loose density of the upper sands, moderate slope of the site and slope stability
                constraints, the site is classified Class P in accordance with AS2870-2011. However, the natural soil
                profile at the site would exhibit the characteristics of a Class S site with an approximate characteristic
                surface movement (ys) of up to 20 mm.

                No design loadings were available at the time of reporting, however it is noted that a suspended first floor
                slab is proposed, and in some areas structure loads may be relatively high. Footings for the proposed
                extensions and carport (including retaining walls and pool) must penetrate through any fill and unsuitable
                soils to be founded at least 1 m into medium dense (or denser) sands and be founded a minimum of 3 m
                BGL (existing ground levels). Steel screw piles would be a suitable footing option for this site.
                It was noted that the eastern side of the residence appeared to have settled previously with cracking and
                vertical separation noted in the blockwork. Based on this evidence it is recommended that the existing
                footings should not be re-used for additional loads imposed by the extensions. Furthermore, it is also
                recommended that the eastern edge of the residence be underpinned using screw piles founded at least 1 m
                into medium dense (or denser) natural sand. Any new internal footings within the existing structure footprint
                (i.e. for new columns, etc.), will need to extend below the existing concrete slab to be founded at least 0.5 m
                into medium dense (or denser) sands at about 2 m depth. Screw piles so founded may be designed using an
                allowable end bearing pressure of 300 kPa.

                Due to the presence of loose sands, together with the close proximity of adjacent structures, open bored
                piles or driven piles are not considered to be suitable for this site. The advice of a specialist piling contractor
                must be sought regarding feasibility, design and installation of the piling system for this site, including an
                assessment of potential vibration effects on nearby structures, and monitoring requirements.

                All footings should be founded such that they are not adversely affected by any adjacent excavations, batter
                slopes, trenches, retaining walls, or in ground structures (e.g. swimming pool) that are not designed to
                support building loads. Footings should be founded at least below a plane extending 1 m horizontally from




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Document Set ID: 23080488
Version: 1, Version Date: 27/06/2024