Geotech Report - Initial Findings

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




       It will be essential to ensure that all services connecting into the site that are to be terminated are properly
       sealed off (including trench backfill) to prevent them becoming water conduits to the site and causing water
       pressure surcharging of excavation support works.

       5.5         Site Settlement

       Provided the subgrade is prepared in accordance with Section 5.3 and no soft/firm clays exist, it is
       preliminarily estimated that subgrade settlement induced by fill placement could be in the range 10mm to
       30mm per metre depth of fill placed, under the weight of the fill alone (i.e. no structure loads applied to the
       fill). Some (additional) settlement will also occur within the fill due to self-weight and these settlements could
       be of the order of 1mm to 3mm per metre of properly compacted fill placed.

       5.6         Foundations

       The site is underlain to approximately 0.8m by fill and/or to approximately 1.2m to 3.9m depth by ‘low
       bearing capacity’ and potentially highly variable, very loose to loose sands, with a reasonably high
       groundwater level. It is therefore considered strip and pad foundations should be extended to found in the
       medium dense sands or the indurated sands. If this is not possible, then buildings could be supported on a
       (preferably non-vibratory) pile system, founding in the medium dense to dense sand and dense, weakly
       cemented indurated sand. Bored piles would be expected to encounter severe construction difficulties and
       their use is not recommended.

       It should be noted that a strength inversions were encountered in the bores and that detailed consideration
       must be given to the presence of the inversion in the selection of foundation bearing pressure and founding
       depth.

       5.6.1       Strip and Pad Footing

       Working bearing capacities that could be used for preliminary design of strip and pad footings are presented
       in Table 5. Footing design will also need to consider footing settlement, which would need to be assessed in
       detail once footing sizes, loadings, layouts and locations are known.
       Table 5: Working Bearing Capacity for Design of Shallow Foundations in Natural Soils
                                                                                                                        (1)
                                                                                              Working Bearing Capacity
                          Material                              Strength
                                                                                                        (kPa)
                        Controlled Fill                          Level 1                                  100
                                                                                                             (2)
                                                             medium dense                                250
                            Sand                                                                             (2)
                                                         dense/weakly cemented                           400
       (1)   Not underlain by ‘softer’ material
       (2)   Given as a guide only and should be assessed before finalising design - dependent upon footing width and
             founding depth

       It is considered that variations in fill, soil strength are likely to occur over the site at founding level and that a
       ‘flexible’ approach would best be adopted to foundation design and construction methodology, so that footing
       sizes/founding depths can be readily adjusted as required during construction, without cost/time penalties
       being incurred. It should also be noted that ‘strength inversions’ were encountered in the bores (i.e. lower
       strength material underlying higher strength material), for example in Bore 11 a layer of loose sand was
       encountered at 6.2m depth underlying medium dense sand.



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