271117 Techtonic GeoTech Cooroy Mtn Rd

Mr Ken Freeman                                                                                  17385-001-Rev0
                                                                                              27 November 2017

All footings should be founded such that they are not adversely affected by any adjacent excavations, batter
slopes, trenches, or retaining walls that are not designed to support building loads. Footings should found at
least below a plane extending 1 m horizontally from the base of trenches/batter slopes/excavations/retaining
walls, then rising up at 1V:1H, as illustrated in the following Text Figure 8.




                            Text Figure 8: Footing depth required to prevent undermining

Footing bases must be cleaned following mechanical excavation to expose undisturbed materials over the
full base area.

If any soil conditions encountered during construction are found to differ from those noted above, Tectonic
must be notified immediately and an inspection carried out to determine if changes to footing design are
required.

5.5   Drainage
The garage extension, carport, and porte cochere should not add significantly to the stormwater catchment
on site, and provided there is capacity, run-off could be directed to the existing provisions on site. If the two
storey extension is to be constructed, then adequate site drainage must be installed to ensure that
stormwater runoff is directed away from the proposed structure and discharged at least 10 m downslope. It
is recommended that surface drainage be installed around the entirety of the house, e.g., swales, or grated
channel drains, to divert any run-off away from the building walls and footings.

Subsurface drainage must also be installed behind all retaining walls to prevent development of hydrostatic
pressure.

For the proposed filling works north of the existing house, a specific arrangement is recommended. It is
understood the existing pool structure will not be demolished, but is to be in-filled. To prevent saturation of
the pool backfill, it is recommended that the front (northern) wall of the pool is broken out, and a 150 mm
thick layer of drainage gravel placed in the base of the pool with an overlying layer of geofabric. The water
should be piped from a collection pit to the extremities of the fill embankment (discharging away from fill
batters), or through weep holes/outlets through the retaining walls. The pool should not be drained through
the bottom as this may saturate underlying foundation soils.
All excess stormwater collected from the site, must be directed by pipes or rock-lined channels to a natural
drainage line at least 10 m down slope of the proposed house. The drainage outlet should be protected by a
stacked or grouted rock weir, or similar, to dissipate stormwater flows. Subsurface disposal of stormwater
must not be undertaken.




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