Reference Documents - RAL22/0032

                Contour Consulting Engineers                                                                    23038-001-Rev0
                                                                                                                  6 March 2023

                4.0       RECOMMENDATIONS
                General recommendations to help maintain the stability of the site are given in the document Some
                Guidelines for Hillside Construction, which is attached.

                4.1     Site Layout and Development Limitations
                The planned extents of the proposed driveway alignment as described in Section 1.1 are acceptable from a
                slope stability viewpoint. Should any revisions be made to the proposed extent of the development, Tectonic
                must review these prior to construction to assess if there are any impacts on slope stability.

                4.2     Earthworks
                Provided sections indicate that the driveway will primarily be cut into the slope, requiring excavations up to
                about 1 m deep, with filling <0.5 m high required for the crossover. Should proposed earthworks exceed
                these quantities, Tectonic must assess the impacts on slope stability before construction.

                4.2.1 Site Preparation and Trafficability
                Any organic rich topsoil, uncontrolled fill, firm/loose (or weaker) soils and overly wet materials must be
                stripped and removed from the construction area. Topsoil materials must not be used in structural fill;
                however, may be placed across landscaping areas. It is recommended that the subgrade should be proof
                rolled using a minimum 4 tonne pad foot roller to identify any ‘soft spots’. Any such soft spots should be
                excavated and replaced with select fill material, constructed as recommended in Section 4.2.3.

                The subgrade materials exposed after site stripping and excavations are expected to comprise stiff (or stiffer)
                clays. The clayey soils could be subject to strength loss from repetitive vehicle loading (particularly from
                rubber tyred plant) or if they become wet. Due to the potential for poor trafficability during and after wet
                periods, placement of a minimum 150 mm thick granular working platform may be required, particularly along
                access ways and any laydown areas.

                The site should be graded to shed surface water runoff away from construction areas. It should be noted
                that during wet weather, the natural soils may cause turbid stormwater run-off. Appropriate erosion and
                sediment control measures must be installed prior to commencement of earthworks at this site.

                4.2.2 Excavations
                Excavations should be achievable using small to medium sized conventional earthmoving plant
                (e.g. 5 to 14 tonne excavators) with toothed buckets, or ripper attachments.

                Temporary, non-surcharged batter slopes may be formed at 1V:1H in the stiff/medium dense (or stronger)
                soils, provided groundwater seepage is not encountered. Flatter batters may be required if groundwater
                seepage is encountered, or if earthworks are undertaken during a period of heavy rainfall. Permanent non-
                surcharged batters in stiff/medium dense (or stronger) natural soils and controlled fill up to 1 m in height must
                be formed no steeper than 1V:2.5H. We note that the design specifies maximum batters of 1V:4H which
                would enable vehicular access, such as for mowing. Where such battering is not possible, temporary and/or
                permanent retention will be required. Any permanent soil and fill batters will require erosion protection (e.g.
                revegetation or surface protection).
                Any excavation required adjacent to existing structures will need to be specifically designed to ensure that
                the structures are not undermined.

                Care should be taken to ensure excavations do not cause excessive ground vibrations that could result in
                damage to existing nearby structures. Should vibratory excavation or construction techniques be adopted,
                ground vibrations should be monitored, and excavation methods may need to be altered should adverse
                impacts be anticipated or encountered. It would be prudent to conduct a dilapidation survey of nearby
                structures before commencement of construction.

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




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Document Set ID: 22374434
Version: 1, Version Date: 14/04/2023