File: 9049 Appendix.docx Memorandum Ground settlement and tilt estimates for GOP cross vein and Wharekirauponga Access Tunnel dewatering A1.0 INTRODUCTION This memorandum summarises the assumptions and results of two-dimensional (2D) seepage and deformation numerical modelling of GOP cross vein and Wharekirauponga Access Tunnel dewatering. The modelling was undertaken to enable estimates of settlements due to dewatering. The analyses have been undertaken using Geostudio 2D finite element analysis (FEA) programs, SEEP/W and SIGMA/W (Refs. 1 and 2). The SEEP/W model of the ground and groundwater parameters for GOP cross vein assessment were provided by GHD (Ref. 4). The Wharekirauponga Access Tunnel model is based on work undertaken by EGL for MUG and MOP4 (Ref. 3). A2.0 SCOPE OF WORK The scope of work has included: i. Modelling of seepage and drawdown associated with dewatering of deep groundwater systems from the depressurisation around the Wharekirauponga Access Tunnel using SEEP/W. ii. Modelling of seepage and drawdown associated with cross vein dewatering caused by the Gladstone Open Pit excavation as modelled by GHD (Ref. 37) iii. Deformation analyses using SIGMA/Wwith changes in stress due to vein dewatering and tunnel depressurisation estimated by the SEEP/W modelling. A3.0 SOIL PROFILE AND GROUND MODEL Figure A1a and Figure A1b provides the model geometry and the associated boundary conditions for the Wharekirauponga Access Tunnel assessment base condition (i.e. before tunnelling). The model was constructed as four layers. From the surface these layers were: younger volcanic rocks, weathered andesite, and undisturbed andesite comprising higher permeability (K) andesite and lower K andesite. The higher K and lower K andesite are both referred to as undisturbed andesite rock mass in this document. The model base extends down to RL255. Figure A4a and A4b provides the model geometry for settlement estimations caused by the Gladstone Open Pit excavation dewatering of the veins. The model was constructed as three layers. From the surface these layers were: younger volcanic rocks, weathered andesite, and undisturbed andesite. The model base extends down to RL900.
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