Attachment 5 - Slope Stability Assessment · RAL20/0005

Mr Peter Loxton                                                                               16162-001-Rev0
                                                                                                 22 July 2016

Any bared areas must be revegetated with similar native shrubs and trees, and ground cover.

Due to the close proximity of a tennis court on the neighbouring property to the north, it is essential that
earthworks be carried out in a fashion to minimise ground vibrations. No vibratory equipment should be used.
It would be prudent to conduct a dilapidation survey of nearby structures prior to construction in order to
establish a ‘baseline’ of structural condition.

4.2       Footing Design
We concur with the structural design in that the proposed residence and any associated structures should be
supported on a piled footing system, with screw piles the preferred method given the ground conditions,
access, etc. Such piles must penetrate through any loose sands to found into medium dense (or denser)
natural sand. Based on the CSI boreholes, a minimum founding depth for piles of 3 m is recommended,
however care will need to be taken during installation to ensure that piles are not over extended. Footings
so founded may be designed using an allowable end bearing capacity of 300 kPa. Given the proposed loads
on the piles, to confirm pile toe levels for design, it would be prudent to conduct more detailed geotechnical
investigation (e.g. mechanical augering to greater depth) once vehicle access to the building site is available.

All footings must also found 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 diagram.




                            Text Figure 11: Footing depth required to prevent undermining


4.3       Retaining Structures
We recommend the following parameters may be adopted for retaining wall design:

          Soil type                                Loose sand
          Friction Angle:                          27°
          Active Earth Pressure Coefficient:       0.4
          Passive Earth Pressure Coefficient:      2.6
          Unit Weight:                             18 kN/m³

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




                                                         9/10