Geotech Report - Initial Findings

Essence of Peregian
215-219 David Low Way, Peregian Beach
Project No. 007-160A,
27 April 2010



       It is suggested that an experienced engineer inspect all footing excavations prior to casting to ensure bearing
       capacity at foundation level is adequate, as there is potential for ‘softer/looser’ materials to be present on
       site. Care should be exercised in the selection of footing founding depths where excavations or natural
       slopes exist (or will exist in the future).

       All footing excavations should be clean, dry and free of loose/softened materials immediately prior to casting.

       5.6.2         Pile Foundations

       Maximum working bearing stress that could be adopted for preliminary design of single axial compression
       loads for piles, founding in sands are given in Table 6. These pressures must be confirmed by testing during
       installation. Potential ‘interaction’ effects must be carefully assessed where piles are closely spaced. It will
       be necessary to carefully consider the effects on foundation performance if soil of lesser strength is located
       below founding level.
       Table 6: Maximum Working Bearing Pressures for Pile Design

                                                                                                                                       (1)
                                                                                                    Maximum Working Bearing Pressure
                            Material                                   Strength
                                                                                                                 (kPa)


                                                                  medium dense                                     600
               Sand/Silty Sand/Indurated Sand
                                                              dense/weakly cemented                               1,000

       (1)
             For a pile length to base diameter ratio greater than 4.0 and no ‘softer’ underlying layers


       If screw piles are considered for support of buildings, it should be noted that they would not be expected to
       provide significant lateral capacity unless significantly ‘raked’.

       The installation of driven piles will involve noise and vibration, and it will be necessary to properly assess any
       potential adverse effects that noise and vibration may have on surrounding structures, existing in-ground
       services etc.

       5.6.3         Raft Foundation

       For the preliminary assessment of the performance of a stiffened raft foundation, the soil parameters
       presented in Table 7 could be used. The parameters have been based on the results of the investigation,
       past experience and published correlations. Detailed analysis will be required if a raft option appears
       feasible.
       Table 7: Soil Settlement Modulus Values

                           Material                                 Strength                       Settlement Modulus
         Controlled fill (Level 1, see Section 5.3)                      -                                 10 – 20
                                                                                                            (MPa)
                                                                             (1)
                                                                   very loose       Vibration sensitive – not possible to reliably predict
                                                                                                                 (2)
                                                                      loose                               7 – 15
                Sand/Silty Sand/Indurated Sand
                                                                  medium dense                             20 – 50
                                                              dense/weakly cemented                        40 – 80
                                        Poisons Ratio ( )                                                        0.3
       (1)
              Not recommended for settlement sensitive structures. Very loose sands will be sensitive to vibration and liquefaction
              effects. Liquefaction potential should be checked as part of detailed design.
       (2)
              Difficult to reliably predict and sensitive to vibration



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