Geotech Report - Initial Findings

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



       It is expected that some variability in material properties will occur across the site, however it is considered
       that they should generally be within the range noted. Despite this variability, it would be generally expected
       that the ‘higher’ modulus values are more likely to be applicable for short-term, transient loads (e.g. wheel
       loads) whilst the ‘lower’ modulus values are more likely to apply to long-term loads.

       5.7         Retaining Walls

       Where sands are retained, non anchored retaining wall pressures could be based on the lateral earth
       pressure coefficients given in Table 8, where a horizontal ground surface is retained in conjunction with a
       triangular pressure distribution, provided the excavation is not surcharged by adjacent buildings/services and
       some movement tolerance exists.
       Table 8: Lateral Earth Pressure Coefficients
                                                                             Unit          Lateral Earth Pressure
                        Material                          Strength          Weight              Coefficient (K)
                                                                                 3
                                                                            (t/m )        Cantilever         Propped
                                                      very loose to loose     1.8           0.40                0.60
        Sand/Silty Sand/Indurated Sand                  medium dense          2.0           0.30                0.50
                                                    dense/weakly cemented     2.1           0.25                0.40


       Where retaining walls are located on (or close behind) slopes, global stability of the overall slope must also
       be checked (i.e. check for potential instability of materials occurring beneath the wall footing). Careful
       consideration will also need to be given to wall and/or structure detailing, where settlement sensitive
       structures/features are located ‘close’ to the top of ‘flexible’ retaining walls.

       Prop loads for unsurcharged propped shoring walls could be designed based on a uniform pressure
       distribution with depth, equivalent to 5H (kPa) where H is the depth of the excavation.

       Even if a drainage system is installed behind retaining walls, it would still be prudent to allow for elevated
       water pressures to act on the walls as elevated groundwater levels may occur due to blocked drainage
       systems.

       5.8         On-Ground Slabs and Pavements

       Subgrade properties will vary across the site following earthworks, and detailed assessment/testing will be
       required at the time of construction in order to confirm design values. Preliminary design of on-ground slabs
       and pavements, cast over a natural soil, or controlled fill subgrade, could be based on the parameters
       presented in Table 9. The values presented in Table 9 are based on the assumption that the subgrade is
       prepared in accordance with Section 5.3.
       Table 9: Subgrade Design Parameters
                                                                                                            (1)
                                                                             Modulus of Subgrade Reaction
                        Subgrade Type                      CBR (%)
                                                                                        (kPa/mm)
              Silty Sand (natural or controlled fill)       5 – 10                       30 – 50
                 Sand (natural or controlled fill)          8 – 10                       40 – 50
       (1)
             For transient loading only




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