Reference Document - Geotech Report - MCU24 0094 · MCU24/0094

                              PROPOSED RESIDENCE
                              33 ROSS CRESCENT, SUNSHINE BEACH

(e.g. sheet piles) or propping will be required as per the recommendations in Section 6.3 below.
Excavations in close proximity to existing structures and infrastructure, including on neighbouring properties
and the road corridor, will need to be specifically designed to prevent undermining. If undermining is a
potential issue the existing structures may need to be underpinned or excavations may require temporary
shoring.
The advice of a suitably qualified and experienced structural RPEQ 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).

6.1.3       Filling
The natural sandy soils where free of deleterious materials (e.g. vegetation, organics etc.) may be reused as
structural fill (retained under the building), subject to appropriate moisture adjustment. It should be noted
that compaction of such relatively ‘clean’ sands as structural fill requires the addition of substantial volumes
of water (‘flooding’) combined with the use of vibratory compaction equipment (typically a smooth drum roller
or heavy vibrating plate). Should importation of fill be required, it is recommended that such fill should
comply with the following:

       Minimum CBR of 10 %
       Maximum plasticity index of 15 %
       Shrink-swell index ≤ 1 %
       Maximum particle size of 100 mm

The primary recommendation would be to re-use site won material, or use a similar granular soil where
import is required. In compliance with above, cohesive soils may be tolerated, however their use should be
limited to lower layers in fill (at least 1 m below surface) and impacts on site classification (Ref. Section
6.2.1) must be assessed by designers.

Any fill should be compacted at moisture contents within the range of ±2 % of optimum moisture content for
Standard Compaction. Fill material should be placed in 250 mm thick (loose thickness) layers and be
compacted by repeated rolling using a minimum 4 tonne smooth drum roller (or equivalent, with 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 details for control
and testing of fill are given in Australian Standard AS 3798-2007 Guidelines on Earthworks for Commercial
and Residential Developments.

6.2       Building Foundations
6.2.1       Indicative Site Classification
Site classification for footing design is determined in accordance with AS 2870-2011 Residential Slabs and
Footings, and depend on the depth of cut / fill undertaken at a site, variations in the natural soil profile, and the
reactivity of the in situ soil and any imported fill materials.

Based on the results of the investigation, the site is classified as Class P in accordance with AS 2870-2011
Residential Slabs and Footings, due to the presence of poor bearing capacity soils at shallow depths, and
trees. If not for these factors, the site would have the characteristics of Class S, with the estimated
characteristic surface movements (‘ys’) ranging up to about 20 mm. However, due to the potential variability
in subgrade density a site classification of Class M is recommended in relation to assessment of flexibility
requirements for ground slabs, footing and plumbing design.




18 June 2024
Report No. 24096-001-Rev0                                15