Approved Plan - OPW21-0279

Anthony Kelly                                                                                      21354-001-Rev0
                                                                                                17 September 2021

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

4.1       Site Layout and Geotechnical Constraints
The earthworks undertaken at the site have been minimal in scope, and largely exploit existing features,
aided by the topographical position close to the crest of a well rounded ridgeline. We understand that the
driveway extension, southern cleared area, and formalised trackway may be asphalted at surface in the
future, which would be acceptable from a slope stability perspective.

The below recommendations have been made as a minimum from a slope stability perspective, and it is
noted that the works extant are in general accordance.

4.2       Earthworks
No further cutting (with the exception for remediation works) or filling is anticipated within the scope of the
earthworks. If further significant earthworks are planned Tectonic must review potential impacts on slope
stability.

Ground surfaces should be graded to shed surface water runoff away from construction areas.
Permanent batter slopes in natural soil consisting of stiff (or stiffer) clays should be constructed at a
maximum grade of 1V:2H.

Although trafficability should generally be good in ‘dry’ conditions, the soils could be 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 along access ways. The existing roadbase materials present
should be sufficient from a trafficability perspective.

4.3       Drainage and Maintenance
Apart from the general advice provided above, implementation of the following specific risk minimisation
measures is recommended to maintain a Very Low Risk to property with regards the earthworks undertaken
at this site.

          Ensure that the finished driveway surface has a cross-fall ‘into’ the hillside such that stormwater is
           not allowed to flow in an uncontrolled manner onto the down slope.
          Form a v-notch swale above the crest of the driveway cutting to divert stormwater away from the cut
           batters to a point(s) where the collected stormwater may be transferred down the cut batter and into
           the roadside table drain in a controlled manner (e.g. using a prefabricated or rock-lined chute[s]).
          Install drainage to transfer stormwater flows from the driveway into the natural gully to the east, or in
           the direction of Six Mile Creek to the west.
          Protect approaches to, and any culvert inlets/outlets, from erosion by placement of geofabric and
           rock fill, or similar.
          Regularly inspect and clean out culvert inlets to prevent blockage by leaf litter, soil, vegetation, etc.
          Revegetate any bare soil exposed by the works. Hydromulch has already been placed on soils
           exposed in batters.

It is noted that measures in place at the site at the time of our inspection largely cover the above points,
however, attention to cambering the finished road surface approaching sealing should be considered. The
cleared southern and northern areas should also include a cross-fall (or sections of grading), at no less than
1V:100H to direct surface water to existing fringe drainage and minimise ponding of water at surface.




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