Attachment 4 - Geotech Report · MCU23/0030

                              50 NOOSA PARADE, NOOSA HEADS
                              PROPOSED RESIDENCE

6.1.3        Material Re-Use

Materials excavated for the basement are expected to comprise mostly sands, with some sandy clays. These
materials should generally be suitable for re-use as structural fill, subject to appropriate moisture adjustment
for the placement of such materials, and treatment of ASS where necessary. Internal dewatering prior to bulk
excavation (within a perimeter wall system) would be prudent to enable easier handling of excavated sand
materials for off-site transport and re-use, particularly if groundwater is shallow at the time of construction. It
is estimated that the sands would have CBR values of 7 % or higher once compacted to at least 95 %
Standard density.

6.1.4        Trafficability

After stripping and excavation to the design levels, the basement subgrade is expected to consist of loose to
medium dense natural sands; with the remainder of the site subgrade in near surface areas (following
stripping) expected to feature loose sands (historic fill). Following site preparation, and bulk excavation for
the basement, the subgrade must be inspected by a suitably qualified and experienced geotechnical RPEQ
to determine whether any over-excavation is required to achieve a stable subgrade for construction activities,
and a suitable subgrade for the preferred foundation solution (Ref. Section 6.3).
Where poorly graded, fine grained sands and/or high silt contents are encountered in the subgrade
materials, they could be subject to strength loss from repetitive vehicle loading or if they are left / become
saturated. Thus, the measures outlined below are recommended:
       Grade the base of the excavation (minimum 1V:100H) to achieve positive drainage to a dewatering
        point(s) (e.g. sump-pump), with collected waters then pumped to a suitable discharge outlet (after
        treatment to a suitable quality). Adequate internal dewatering will need to be maintained to achieve
        trafficability.
       Place non-woven geosynthetic filter fabric (e.g. Bidim or equivalent) across the subgrade to prevent
        ‘pumping’ of ‘fines’ (silt materials) into the rock fill working platform. The grade of geosynthetic to be
        used will be dependent upon the particle size of the selected granular material used (see below).
       Construct a minimum 150 mm thick granular working platform to the design subgrade level. We
        suggest the use of 75 mm to 150 mm rock fill with a thin capping layer of CBR 15 % material to
        provide a smooth working surface.
Specific design will need to be carried out to determine working platform requirements for any heavy plant
(e.g. mobile cranes or piling rigs), and a thicker rock fill platform may be required than recommended above.

6.1.5        Filling

Based on the supplied architectural drawings, and the proposed construction methodologies, minimal
structural filling works are anticipated as part of the development. To achieve non-worsening of the global
stability of the rock revetment along the river to the north, filling should not exceed 0.5 m high above the
existing ground surface unless assessed and approved by a geotechnical RPEQ prior to construction.
It is recommended that any imported fill for the project comprise good quality, low reactivity materials (e.g.
non-descript crushed rock, ‘clean’ sands, or similar), that comply with the following:
       Minimum CBR of 10 %
       Maximum plasticity index of 15 %
       Shrink-swell index ≤ 1 %
       Maximum particle size of 100 mm
Fill material should be placed in 200 mm thick (loose thickness) layers and be compacted by repeated rolling
using a minimum 4 tonne roller (vibration on if safe to do so) to achieve a dry density ratio of at least 95 % of
the maximum Dry Density Ratio (DDR), based upon the Standard Compaction method, or a Dry Density
Index of at least 70 %. Confirmatory compaction testing must be carried out at regular intervals. A minimum
of two tests per vertical lift is recommended where structural fill heights are to exceed 300 mm. Further



2 February 2023
Report No. 22500-001-Rev0                                8