RFI - Attachment D - Geotechnical Investigation Report · MCU25/0053

                                                                                                                              PTG/01608 – 0001 – Rev0

Table 7: Ultimate Geotechnical Design Parameters for Bored or Driven Piles
                Material Type                               Ultimate Skin Friction (kPa)                        Ultimate Base Bearing (kPa)
           Loose sand/silty sand                                  Not Recommended                                   Not Recommended
     Medium dense sand/silty sand                                              2                                           500
           Dense sand/silty sand                                               4                                           1000
Notes: Assuming pile is founded to a minimum depth of 1.5 m and top 1 m of pile is ignored for skin friction.

As with the high-level foundations, bearing capacity in sands increases with depth. If bearing capacities at deeper
depths are required, they can be provided.

The above parameters are only suitable where the excavation of piled foundations are supervised and at a minimum
inspected by a suitably qualified geotechnical engineer to confirm the founding conditions and materials encountered
in the side walls.

The design of piled foundations should be undertaken in accordance with:
» AS 2159-2009: Piling - Design and installation;
» Any other relevant design standards (Australian or international); and
» Engineering Principles.

The piled foundation design should also consider:
» Piles should be founded a minimum of two pile diameters into the nominated strata and have a minimum pile
    length of four times the pile diameter;
» The upper 1 m of pile length should be ignored due to pile load development and shrink swell effects; and
» Settlement of properly designed and constructed footings should be less than 1% to 2% of the pile diameter.

To calculate the design geotechnical strength (Rd,g), the ultimate geotechnical strength should be multiplied by a
suitable geotechnical strength reduction factor (фg) as per Section 4 of AS 2159–2009. The geotechnical strength
reduction factor (фg) is based on:
» фgb = The basic geotechnical strength reduction factor, calculated using a risk assessment procedure;
» фtf = Intrinsic testing factor, based on the type of pile testing adopted; and
» K = The testing benefit factor, based on a percentage of the piles that are tested.

Typically, where no pile testing is undertaken and the piles have a low redundancy, the assessed risk rating would be
high and a фg value of 0.45 would apply. It should be noted this assessment has been undertaken by PTG to assist
with the design of the foundations, however as assessment of each risk rating and factors must be undertaken by the
designer of the piles for the final design.

Specialist piling contractors should be consulted when selecting and installing piles.


            RETAINING WALL PARAMETERS
It is understood that retaining walls will be required for the development. Retaining wall type and height are unknown
at the time of writing this report.

Any retaining structures at the site should be designed in accordance with AS4678-2002 ‘Earth Retaining Structures’.
Retaining wall design should consider the below:
» The distance from the crest and magnitude of any surcharge loads (ie buildings, roads);
» Whether the selected wall type is suitable for the proposed loading conditions;
» Wall geometry and the presence of any slopes at the crest or toe of the wall; and
» Type of backfill to be used behind the wall, and whether compaction will exert additional forces onto the wall.

Table 8: Geotechnical Parameters for Retaining Wall Design
                                                  Bulk Unit Weight                       Drained Cohesion              Effective Friction Angle
           Material Type
                                                        (kN/m )   3
                                                                                                (c’ kPa)                         (φ’ °)
      Loose sand/silty sand                                  17                                     0                             28
    Medium dense sand/silty
                                                             18                                     0                             30
            sand
      Dense sand/silty sand                                  19                                     0                             32
  Very dense sand/silty sand                                 20                                     0                             35

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