Appendix E - Geotechnical Report

                              PROPOSED RECONFIGURATION OF A LOT
                              216 BLACK MOUNTAIN ROAD, BLACK MOUNTAIN

7.0      ENGINEERING ASSESSMENT
7.1      Earthworks
Preparatory cut and fill activities have not been indicated by Murray or the client in advance of the
geotechnical investigation. However, based on the building envelope given, and the assumed likely building
position being towards the south (upslope side) of the envelope, cut/fill depths/heights in the order of 1 m
would be permitted from a slope stability point of view. Should future cut/fill exceed this, the
recommendations contained in this report must be reviewed by Tectonic.

7.1.1        Site Preparation and Trafficability
Organic rich topsoil and any uncontrolled fill (e.g. over the proposed driveway alignment) should be stripped
from future construction and filling areas and be set aside. Based on the test pit results stripping depths
across the proposed building envelope to remove organic rich topsoil should be in the order of 0.2 m BGL
however, deeper pockets of topsoil may be present across the site. Organic rich topsoils must not be re-
used as structural fill, however may be retained on site for later use across landscaping areas, if required.
Following clearing and topsoil stripping, the exposed subgrade materials are expected to comprise mostly
stiff (or stiffer), high plasticity, silty clays. Residual and extremely weathered clay materials, such as those
found on site, are subject to strength loss from repetitive vehicle loading, particularly from rubber tyred plant,
or if they become 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 across laydown areas and
site access tracks.

The stripped subgrade in proposed fill areas should be inspected by an experienced engineer prior to
placement of fill. All subgrade areas should be proof rolled by a minimum 4 tonne roller to identify any
soft/loose material. Any soft/loose material should be over-excavated to expose a stiff (or stiffer) foundation
and then backfilled with compacted select material as recommended in Section 7.1.4.

The site should be graded to shed surface water runoff away from proposed building envelopes. Swale
drains should be constructed along the toes of any cuts, and along the upslope extents of construction areas
to intercept runoff from upslope. The drains should be graded to discharge collected waters to a control
point before being released to a suitable area on-site e.g. natural gullies/drainage lines away from the
construction area.

Appropriate erosion and sediment control measures must be installed prior to commencement of earthworks.

7.1.2        Excavations
Excavations could extend to depths of up to 1 m for earthworks cut activities, and possibly deeper subject to
construction requirements. Subsurface conditions are anticipated to be within the excavation limits of small
to medium sized excavators with toothed buckets (i.e. 6 tonne to 12 tonne). Should excavations extend more
than 0.5 m in to the phyllite bedrock, ripping or pneumatic breaking attachments, together with larger
equipment, may be required.

7.1.3        Batter Slopes
Temporary cuts in the natural stiff (or stiffer) silty clay should be formed no steeper than 1V:1H. Flatter
temporary batters may be required if groundwater seepage is encountered, or if earthworks are undertaken
during a period of heavy rainfall. Permanent cuts in natural stiff (or stiffer) materials and controlled fill batters
may be formed at 1V:2H. Cuts in weathered phyllite (rock) may be constructed at 1.5V:1H (subject to
confirmation be a qualified geotechnical engineer). Alternatively, cuts/fills could be retained by engineer
designed retaining walls.

The above recommendations do not supersede any existing safety regulations or legislation applicable to
excavations e.g. limits on personnel entry into trenches.

Batter faces must be protected from erosion (e.g. vegetation or geosynthetic erosion matting).




19 June 2018
Report No. 17427-001-Rev0                                 9