J001701-006-R-Rev1_Medihub_Geo

Stockwell



Ancillary or isolated structures not part of the basement structure could be supported on high-level strip or
pad footings, with maximum 25 mm settlement, as follows:
        Stiff natural clay:          100 kPa ABP
        Very stiff natural clay:     200 kPa ABP
        Hard natural clay:           300 kPa ABP

    6.3.3 Piled Footings
If settlements/stresses are found to be excessive below peak loads in parts of the raft slab (e.g. under
columns or lift cores), piles may be required below peak loads. The proposed building design may also
require tension piles at selected locations outside of the building superstructure envelope to resist
hydrostatic/uplift pressures and overturning forces, or piles for ancillary structures.
Bored concrete or continuous flight auger (CFA) piles could be considered. Driven piles may not be suitable
due to vibration impacts on adjacent structures.
Indicative pile design parameters are provided in Table 1. Settlement of the piled footings is expected to be
in the order of 0.5% of the pile width. Ultimate geotechnical capacities (Rd,ug) determined from the
parameters provided must be multiplied by a geotechnical strength reduction factor (øg) in accordance with
Section 4 of AS 2159-2009 Piling – Design and installation to determine the design geotechnical strength
(Rd,g). The geotechnical strength reduction factor should be determined in accordance with AS 2159-2009
and is expected to be in the range of 0.45 to 0.55. An upper bound value may be adopted if supervision and
certification of pile construction is carried out by a geotechnical engineer. Ultimate (unfactored) geotechnical
parameters for pile design are shown below in Table 1.
For temporary basement retention (if required), the lateral capacity of a pile is provided by the passive
resistance of the surrounding soil. The soils to a depth 1.5 times the pile diameter below the excavated
surface should be ignored in the assessment of lateral capacity. The lateral capacity of piles may be
determined using various methods, and which generally require an estimation of the Young’s modulus (Es) of
the founding stratum.
Specialist piling contractors should be consulted regarding selection of suitable pile types, detailed design of
piles, the potential vibration effects caused by pile driving and suitable dynamic pile testing methods and
testing frequency.
Table 1: Recommended values for raft or pile design.
                                       Unit                                                         Ultimate        Ultimate
                                                  Undrained         Elastic
                                     weight                                        Poisson’s          skin            base
            Material type                         Cohesion         Modulus
                                        Ƴ                                            Ratio          friction       resistance
                                                  (Cu) (kPa)        (MPa)
                                     (kN/m3)                                                         (kPa)            (kPa)

 Stiff Clay                             18            50              8-20                              20              NR
 Very Stiff Clay                        19            100            15-40           0.2-0.3            50              NR
 Hard Clay/EW Sandstone                 20            200            40-70                              80            1,800
Notes:
    1)   NR – Not recommended
    2)   Skin friction should be discounted for sections of pile shafts where liners are in place.
    3)   Indicative modulus values taken from published paper, Site Characterisation, Terence Wiesner, Australian Geomechanics –
         Dec 1999 and ‘Foundation Analysis & Design (Bowles, 4th Edition)
    4)   Below the groundwater level the submerged unit weight of the soil should be adopted.

    6.3.4 Footings - General
To achieve the design parameters, founding materials must be dry and cleaned of any loose, disturbed or
saturated materials prior to pouring concrete. If any soil conditions encountered during footing excavation are
found to differ from those noted in the geotechnical investigation, Core should be notified immediately, and
further assessment carried out to determine if changes to footing design are required. The footings
excavations should be assessed by a geotechnical RPEQ to confirm founding material.




J001701-006-R-Rev1                                                                                                  Page 7