Reference Documents

                                          PROPOSED SUBDIVISION
                                          41 TALLOWWOOD PLACE, BLACK MOUNTAIN

            6.2         Earthworks
            6.2.1         Site Preparation and Trafficability

            Following clearing of vegetation (where required), tree stumps and large roots must be ‘grubbed out’ and any
            organic rich topsoil, firm/loose (or weaker) soils, colluvium/slopewash, overly wet materials and any
            uncontrolled fill must be stripped and removed from the proposed development area. Topsoil materials must
            not be used in structural fill; however, may be placed across landscaping or effluent disposal areas (if
            required). It is recommended that, following removal of unsuitable materials, all building/pavement
            subgrades should be proof rolled using a minimum 4 tonne roller in the presence of a civil/geotechnical
            RPEQ to identify any ‘soft spots’. Materials in any such soft spots should be excavated and replaced with
            select fill material, constructed as recommended in Section 6.2.4.
            Based on the results of the investigation, it is likely that excavation depths up to about 0.3 m will be required
            to remove the existing topsoil; however, deeper pockets may be present across the building envelope.

            After stripping, the subgrade is expected to comprise mostly very stiff residual clays of high plasticity, tending
            towards clayey silt, grading to weathered phyllite in areas of deeper excavations. The cohesive (clay/silt)
            materials would be subject to strength loss from repetitive vehicle loading (particularly from rubber tyred
            plant) or if they become overly 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 laydown areas.

            Wherever possible, due to the potential loss of strength under elevated moisture content and sensitivity of
            the natural subgrades, light construction equipment should be utilised and trafficking of subgrades should be
            minimised. Subgrades should be graded and ‘sealed off’ at the end of each working day using a smooth
            drum roller to prevent ponding of water and aid shedding of runoff, so that the risk of subgrade softening is
            minimised. Earthworks would likely be particularly prone to disruption due to wet weather, which should be
            considered accordingly during project planning.

            The site should be graded to shed surface water runoff away from all construction areas. Swale drains
            should be constructed along the toes of any cuts, and above cuts where possible, with the drains graded to
            discharge collected waters to a control point away from any effluent disposal area before release off-site.
            Appropriate erosion and sediment control measures must be installed prior to commencement of earthworks
            at this site.

            Specific design would need to be carried out to determine working platform requirements for any heavy plant
            (e.g. mobile cranes and piling rigs), and a thicker rock fill platform may be required than suggested above.

            6.2.2           Excavations
            Excavations in the natural soils and very low to low strength phyllite to the test pit termination depths should
            be achievable using conventional earthmoving plant, such as medium to large (8 to 20 tonne) excavators
            with toothed buckets and/or ripper attachments (i.e. the material is rippable).

            As indicated by toothed bucket refusal and very slow digging at depths of about 1.7 m and 2.3 m BGL, low
            strength (or stronger) phyllite would be expected in deeper excavations. Excavations into any low strength
            (or stronger) weathered phyllite may require the use of ripper and/or hydraulic rock breaking attachments
            with large equipment (e.g. 20 to 40 tonne excavator(s)), particularly in any confined excavations (e.g. service
            trenching). If high strength (or stronger) weathered phyllite requires excavation, other specialised excavation
            methods (e.g. pre-splitting the rock using ‘Nonex’) may be required.

            Excavations will need to be carefully monitored and managed so that excessive ground vibrations do not
            cause damage to neighbouring structures.

            Should groundwater seepage be encountered during construction, such seepage should be readily
            removable using gravity drainage at a low point in the excavation.




             22 May 2023
             Report No. 23099-001-Rev0                              14

Document Set ID: 22826802
Version: 1, Version Date: 23/02/2024