Attachment 12 - Geotechnical Investigation Report

                                    PROPOSED RETIREMENT DEVELOPMENT
                                    MYALL STREET, COOROY

All footings should found such that they are not adversely affected by any adjacent excavations, batter
slopes, trenches, or retaining walls that are not designed to support loads. To minimise the potential for any
adverse interaction effects, footings should found at least below a plane extending 1 m horizontally from the
base of trenches/excavations/retaining walls, then rising up at 1V:1H. This requirement is illustrated in Text
Figure 9 below.




                        Text Figure 9: Footing depth required to minimise risk of undermining

6.3 Retaining Structures
Recent preliminary bulk earthworks and civil proposals supplied to us show that retaining structures of
between about 3 m and 5 m height are intended to the north and south of the site.

We have provided the following parameters, given in Table 4 below, to enable furthering of preliminary
design options. Once a specific arrangement has been proposed, this should be verified from a global
stability perspective. This would be particularly important for the retaining structure proposed to the north-
west of the site, above the existing creek bank.

Design for retaining walls could be carried out using a triangular pressure distribution applicable to the wall
type. The values in Table 4 assume that the walls are fully drained, and no allowance is included for
hydrostatic pressures, construction loading, up-slope footing loadings, the effects of sloping ground and
backfill compaction stresses.
Table 4: Retaining Structure Design Parameters
                             Unit                                   Lateral earth pressure coefficients
                                           Friction
                            weight
 Retained material                        angle, Ø’
                            (kN/m3                               Ka                      Ko
                                         (Degrees)                                                        Kp
                               )                          (Cantilever wall)      (Non-yielding wall)


   Natural Very Stiff
                              1.8            28                  0.36                    0.53             2.77
   (or stiffer) Clays


         Controlled
                              1.8            26                  0.39                    0.56             2.56
        Level 1 Fill*


   Very Low Strength
                              2.1            35                  0.27                    0.43             3.69
  (or stronger) Rock**

Note:     *         depends on fill material type and level of compaction.
          **        subject to confirmation during further site investigation (Ref. Section 6.6)




17 May 2019
Report No. 19071-001-Rev0                                      12