Slope Stability Report-21190-001-Rev0 Pomona Kin Kin Rd

Phil Brierley                                                                                    21190-001-Rev0
C/- NDD Constructions Pty Ltd                                                                       21 June 2021

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.

4.4       Retaining Walls
Retaining structures must be founded as described in Section 4.3 above. Engineer design and certification
of retaining walls is required where such walls:

          Exceed 1 m height.
          Are subjected to surcharge loads (e.g. from backslope, adjacent structures, etc.).
          Are located within close proximity to existing structures.

Retaining structures should be engineer designed in accordance with AS4678-2002 Earth-retaining
structures. We suggest the following parameters may be adopted for retaining wall design:

          Friction Angle:                          25° (clay soils)           35° (weathered rock)
          Active Earth Pressure Coefficient:       0.41 (clay soils)          0.27 (weathered rock)
          Passive Earth Pressure Coefficient:      2.46 (clay soils)          3.7 (weathered rock)
          Unit Weight:                             18 kN/m³ (clay soils)      21 kN/m³ (weathered rock)

These parameters do not include allowance for surcharge above the wall, or additional loads imposed by
sloping ground.

4.5       Drainage
Adequate site drainage shall be installed to ensure that stormwater is directed away from the footings of the
proposed shed and workshop.

It should be ensured that guttering and downpipes around the proposed shed are sufficiently scaled to
minimise overflow on to the building pad and slope below. In addition, diversion drainage should be installed
above the crest of all cut/fill batters. Adequate site drainage must be installed to ensure that stormwater
runoff is directed away from building walls and footings (e.g. positive gradients and/or channel drains), and
also not allowed to flow over fill embankments. Uncontrolled flow of stormwater over cut or fill batters (e.g.
from gutter overflow during high intensity storms) has the potential to saturate and weaken the batter
materials, potentially leading to slumping failure. Future building and landscaping must be carried out to
maintain good drainage.

Specific drainage recommendations are as follows:

          Install diversion drainage along the cut sides of the building platforms. The platforms should be
           graded at a minimum 1V:100H to drain into the diversion drainage system.
          Install/formalise diversion drainage (e.g. swale drain) along the upslope side of the existing driveway.
          Install water bars at regular intervals along the gravel driveway to direct surface water into the swale
           drain along the upslope side of the driveway.
          All areas exposing erosion features (e.g. rill erosion, scours etc.) must be reinstated with select fill
           material, constructed as recommended in Section 4.2.3 and erosion protected.

Subsurface drainage must be installed behind any retaining walls (e.g. slotted ‘aggi’ pipe wrapped in filter
‘sock’ placed in gravel backfill). Depending on matters such as the extent of drainage installed and site-
specific groundwater conditions, the designer must make an assessment of hydrostatic pressure to be
accounted for in the design of the retaining structure.

All collected waters (including overflow from rainwater tanks, etc.) must be directed by pipes or rock-lined
channels to discharge at least 5 m downslope from any structure or embankment. A surface dissipation
device such as rock weir or rock lined contour drain should be installed at the stormwater outlet(s).

Subsurface disposal of stormwater must not be undertaken (including infiltration pits).




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