Our Ref:9049 7 March 2022 Page 2 File: 9049 Appendix - 7 Mar.docx regolith, very strong (VS) andesite, very weak (VW) andesite, strong (S) andesite and weak (W) rhyolite. The model base extends down to RL-300m from RL340m. The parameters summarised in Table A4 have been adopted for SIGMA/W deformation analyses from the dewatering of the vent shaft at WUG. TABLE A4 Material Deformation Parameters for Shaft 2 Material Layer Unit Weight (kN/m3) Young's Modulus (MPa) Poisson's Ratio Regolith 18 30 0.2 Very Strong Andesite 27 8,700 0.2 Very Weak Andesite 27 1,000 0.2 Strong Andesite 27 8,700 0.2 Weak Rhyolite 25 8,700 0.2 A3.3 Wharekirauponga (WUG) Mine Figure A7 provides the model geometry and the associated boundary conditions for the mine assessment base condition (i.e. before dewatering). The SIGMA/W deformation model was applied as four different stiffness layers. From the surface these layers were: regolith, rhyolite pyroclastics, rhyolite flow and andesite flow. The model base extends down to RL600m from RL200m. The parameters summarised in Table A5 have been adopted for SIGMA/W deformation analyses for the depressurisation at WUG. TABLE A5 Material Deformation Parameters for WUG Mine settlement estimate Material Layer Unit Weight (kN/m3) Young's Modulus (MPa) Poisson's Ratio Regolith 18 30 0.2 Rhyolite Pyroclastics 25 1,000 0.2 Rhyolite Flow 27 8,700 0.2 Andesite Flow 27 8,700 0.2 A4.0 MODELLING AND RESULTS Decoupled seepage and deformation analyses using SEEP/W and SIGMA/W have been undertaken for both the vent shafts at (Willows and WUG) dewatering and the tunnel section (at Willows Road Farm). The SEEP/W model calculates the change in pressure associated with dewatering and depressurisation. The SIGMA/W model then calculates the ground deformation that is caused by the change in pressure. Four separate geometries were used to model ground deformations, Vent Shaft 1, Vent Shaft 2, tunnel section at Willows Road Farm and the WUG mine (simplified 1d profile). The vent shaft geometry was modelled for drawdown caused from potential seepage into the vent shafts. The tunnel section modelled local depressurisation into the andesite. The WUG mine geometry is simplified and replicates geology at the mine to estimate the settlement caused from full drawdown to RL-180m.
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