Reference Document - MCU25 0060 (As Published)

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


6.1          Development Limitations
It is anticipated that the main bulk earthworks feature would be the cutting across the site to place the
lower level of the main residence on. This is anticipated to be in the order of 3 m to 3.5 m below existing
levels, and possibly slightly deeper to allow for footings, slab beams and underground services/drainage.
Filling for the ground level is expected to range up to about 1.5 m height on the downslope side (to be
battered); with earthworks elsewhere for localised levelling and landscaping not expected to exceed
0.5 m depth/height.
Should bulk earthworks, or the proposed methodology/extent of works change, Tectonic should be
consulted to re-assess the recommendations given in this report.


6.2          Earthworks
6.2.1        Site Preparation and Trafficability
Following removal of the existing buildings and associated construction elements (e.g. footings, services,
etc.), any tree stumps and large roots should be ‘grubbed out’. Any organic rich topsoil should then be
stripped and set aside. Based on site observations and boreholes, topsoil stripping depths should
generally range between 0.1 m and 0.2 m BGL. It is noted that deeper pockets of topsoil may exist.
Topsoil materials must not be used in structural fill; however, may be placed across landscaping areas.
Unsuitable natural material such as any saturated, loose or soft materials encountered should also be
removed during subgrade preparation for bulk earthworks.
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.
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 poor trafficability during placement of a minimum 150 mm thick granular
working platform may be required on soil subgrades along haul roads and across laydown areas.
Specific platform design would be required prior to mobilisation and trafficking of any heavy mobile
plant on the site (e.g. cranes, concrete pumps or piling rigs).
Construction areas and surrounds should be graded to shed surface water runoff. Swale drains should
be constructed along the crest and toe of any cuts, and above fill batters, where possible. Drains are to
be graded to discharge collected waters to a control point(s) before release into existing stormwater
infrastructure.

Proposed Residential Development
25 August 2025 | 25038-001-Rev0                                                                             13