geotech report · MCU15/0087

Slope Stability and Geotechnical Assessment
1 Natasha Avenue, Noosa Heads




Table 1: Retaining Wall Design Parameters


                                              Friction
                              Effective                    Unit       Active                    Passive
                                              Angle,                               *At Rest
                              Cohesion                    Weight     Pressure                   Pressure
        Description
                                                 (’             3                     Ko
                               (c’, kPa)                 ( kN/m )       Ka                         Kp
                                              degrees)


   Controlled Sand Fill            0            33          19          0.3           0.5           3.3

  Alluvium Sand - Loose            0            28          18          0.36          0.5           2.8

Alluvium Sand – Medium             0            33          19          0.3           0.5           3.3
         Dense

Alluvium Sand – Dense to           0            35          20          0.27          0.5           3.7
       Very Dense

* These are modified rather than in-situ Ko values, assuming that at least a small amount of wall
movement (say about 0.1 to 0.3% of the wall height) could occur.

6.8. Piled Footings
Should piled footings be adopted, it is recommended that all piles be designed in accordance with the
requirements of AS2159 – 2009. Using methods described in Woodward and Boitono (1961) and
Zhang and Einstein (1998), the geotechnical parameters recommended for the pile design are shown
in Table 2.

It is likely that bored piles (non-displacement type) will be adopted on the site. The parameters
assume that the pile base is clear of debris. If seepage occurs in the pile base, dewatering should be
conducted prior to pouring concrete.

Vibrations associated with driven piles could cause instability in the dune escarpment. They should
only be adopted in consideration of all risks. Coffey should be consulted for advice on the use of
driven piles if this option is to be considered.

Screw piers may also be suitable providing they are able to meet the load requirements, that they
have the structural capacity and that they can met the design life requirements.

It should be noted that unit stress design values will vary for different pile diameters and founding
depths, and different values may be applied depending on the type of pile adopted, founding depth,
installation method, level of supervision, static load and pull-out testing (depending on the design
philosophy i.e. pile spacing and whether uplift is the critical load). Pile design should be checked for
serviceability, and for lateral loading that may potentially occur.




Coffey
GEOTKPAR02068AA/A                                                                                          4
12 August 2015