Appendix E - Geotechnical Report

                                 PROPOSED RECONFIGURATION OF A LOT
                                 216 BLACK MOUNTAIN ROAD, BLACK MOUNTAIN

base of trenches/excavations/retaining walls, then rising up at 1V:1H. This requirement is illustrated in Text
Figure 9.




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

7.3            Retaining Structures
Design for retaining structures could be carried out using a triangular pressure distribution applicable to the
wall type and based on the parameters listed in Table 4. 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
                                                                      Lateral earth pressure coefficients
                               Unit
                                          Friction
 Retained material            weight
                                          angle (°)            Ka                        Ko
                              (t/m3)                                                                        Kp
                                                        (Cantilever wall)        (Non-yielding wall)
 Residual Material
 comprising very stiff to       1.9           27               0.38                     0.55                2.66
 hard silty clays
 EW Material comprising
 stiff to very stiff silty      1.8           25               0.41                     0.58                2.46
 clays
 Future fill                     *            *                   *                       *                  *
Note:     * Depends on fill material type and level of compaction.


7.4            Pavement Design Parameters
Based on the general nature of the material encountered during the investigation, design of pavements may
be based upon an indicative CBR value of 3 % for the expected silty clay subgrades.

In general, proposed pavement subgrades must be ‘proof rolled’ and visually assessed by an experienced
engineer to ensure no heaving or unacceptable subgrade deflection occurs. Should heaving or deflection
occur, excavation of ‘soft spots’ may be required, followed by reinstatement with compacted select granular
fill.

The recommended design CBR value is applicable to properly drained subgrades only, and must be
confirmed by subgrade inspection and testing by an experienced engineer following earthworks. ‘Properly
drained subgrades’ require open graded drains, site grades that shed water and prevent ponding, and
subsurface drains adjacent to pavements.




19 June 2018
Report No. 17427-001-Rev0                                    11