Appendix B - Global Stability Assessment Report

                                                    - 11 -
                                                                                        Job No: ME21/032


The global stability analyses indicate that:

Cut Batter

         The existing extremely weathered rock cut batter which is 5.5m high and cut an angle of
          approximately 380 does not achieve a FOS of 1.5 and treatment is required
         To achieve a FOS >1.5, the existing cut batter is required to be:
              o Supported by a 3m high retaining wall (e.g ‘block’ type with steel reinforcement) with
                  controlled filling behind the retaining wall at no steeper than 2.5H:2V, and no higher
                  than 3m above the crest of the retaining wall; or
              o Benched where the existing cut batter height exceeds 4m. The lower batter is to be no
                  higher than 4m and the upper batter is to be no higher than 3.5m. Both batters are to
                  be no steeper than 380 in slope angle, and are to be separated by a bench with a
                  minimum width of 2m.

Fill Batter

         The existing fill batter comprising clay based soils of high plasticity, which is 4.5m high and
          graded at an angle of approximately 350 does not achieve a FOS of 1.5 and treatment is
          required
         To achieve a FOS >1.5, the existing fill batter is required to be flattened to 2.5H:1V, or
          supported by 3m high retaining wall with 7m deep pile embedment in the natural stiff clay of
          high plasticity (‘extremely weathered granite’). Where a retaining wall is constructed, additional
          filling will be required behind the retaining wall to create a slope no steeper than 150 and no
          higher than 1.5m above the crest of the retaining wall.

The analysis information in this section is based on:

         The ground models used in the assessments accurately reflecting the conditions at the batter
          locations.
         The recommendations presented in Section 9.0 being carried out onsite.

9.0       RECOMMENDATIONS

To reduce the potential for future degradation, erosion and general instability, the attached Guidelines
for Hillside Construction (Appendix G) and the following recommendations must be carried out and
maintained:

         Adequate erosion and sediment control must be installed prior to any further earthworks.
          Further advice must be sought from a qualified and competent RPEQ engineer or Certified
          Professional in Erosion and Sediment Control. At a minimum, surface drains must be installed
          upslope of earthworks areas, and discharge in a manner which doesn’t increase the erosion,
          sediment or slope instability risk either at the Site or adjacent to the Site.
         Water must not enter the cut and fill batters or retaining wall areas, and all surface water must
          be diverted behind the crest of the batters and retaining walls to a suitable discharge point, to
          be approved by Council. Water run-off onto or over the batters is not allowed. It is noted that
          the global stability modelling has been carried out assuming that no water infiltrates the batter
          materials, and that the long term groundwater level will be well below the base of the batters
          and retaining walls at all times and over the long term. In addition to suitable drainage behind
          the batter and retaining wall crests, suitably designed drains must be installed at the toes of the
          batters and retaining walls. Surface drains are to have a concrete liner or similar to as to reduce
          erosion and seepage into and below the ground surface in these areas. All drains are to be
          designed by a qualified and competent engineer.
         Subsurface drainage must be provided behind any proposed retaining walls to prevent the
          build-up of groundwater pressures, and must discharge by piped conduits well downslope of
          the retaining wall areas.
         Surface and subsurface drains must discharge in a manner which doesn’t increase the erosion,
          sediment or slope instability risk either at the Site or adjacent to the Site.
         All drainage systems are to be approved by Council.

Ref: 27222-rev 1                                                               MORRISON GEOTECHNIC
Mr Geoff Hussin