Geotechnical Report (1) · MCU21/0212

                             PROPOSED RESIDENCE
                             66 SEAVIEW TERRACE, SUNSHINE BEACH

about 0.2 m and 0.5 m deep; however, deeper areas of unsuitable materials may be present across the site.
Topsoil materials must not be used in structural fill; however, may be placed across landscaping areas.
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 vibrating plate). Care must be taken with the use of vibratory equipment (e.g. compactors or sheet piling)
to ensure that there are no adverse impacts on surrounding structures. The impacts from ground vibration
must be closely monitored and managed during construction. It would be prudent to conduct a dilapidation
survey of neighbouring structures prior to commencement of construction, including underground services
and the stairs to the north.

The exposed natural subgrade following excavations will likely be in a loose condition and must be
compacted by several passes of a vibrating plate or minimum 4 tonne vibrating smooth drum roller, in
conjunction with surface application of ample water, to achieve the required compaction.

Due to the potential for development of poor trafficability during construction, placement of a minimum
150 mm thick granular working platform may be required across laydown areas. Specific platform design
would be required prior to mobilisation and trafficking of any heavy mobile plant on the site (e.g. mobile
cranes, concrete pumps or piling rigs).

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).

6.1.2       Excavations
Excavations through the soils should be achievable using conventional earthmoving plant (e.g. small or
larger excavators with toothed buckets). Temporary unsurcharged cuts in the very loose to loose sand could
be formed at 1V:2H, and at 1V:1.5H in medium dense (or denser) sand, for batters up to 3.5 m in height.
Flatter batters or temporary retention may be required if groundwater seepage is encountered or if sloughing
of dry sand occurs at the batter surface. Deeper cuts, if required, will require temporary shoring, unless
assessed and approved by Tectonic during construction.

Permanent cuts or fills greater than 1 m must be retained. Permanent cut and fill batters up to 1 m high shall
not exceed 1V:2.5H (as was the maximum natural slope present above the main high dune face, around 22°).
Any permanent soil and fill batters will require erosion protection (e.g. revegetation or surface protection).
Similarly, improvements to the vegetation (i.e. with site appropriate natural species) on the natural high dune
face downslope of the residence would aid in restricting the development initial surficial failures.

It is likely that the above temporary batter slopes will not be able to be achieved at least along the western
boundary, due to spatial restraints, and so temporary shoring may be required (e.g. sheet piles) as per the
recommendations in Section 6.3 below. Excavations in close proximity to existing structures and
infrastructure (e.g. sewer main along the western boundary), including on neighbouring properties, will need
to be specifically designed to prevent undermining. It is recommended that footing exposures or
confirmation of existing 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
excavations may require temporary shoring.
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).




23 November 2021
Report No. 21370-001-Rev0                              16