The second model was used to assess the additional inflow resulting from the driving of a second tunnel in close proximity to another. The results of the model were used to factor the results of the analytical model inflows (Attachment B) to replicated the dual tunnels. The model section is 1 km in width and is 600 m deep with a 5 m x 5 m grid spacing. Figure D6 shows the dual tunnel model setup. Figure D6 Dual Tunnel Inflow Model Setup Material Properties The model permeability values adopted were andesite rock (K= 2.5x10-8 m/s), andesite tuff (K=1.0x10-7 m/s) and for a faulted zone (K=1.0x10-5 m/s). The fault was assumed to have a Storativity of 0.01 and the rockmass to be 0.001. Boundary Conditions The surface effects model boundary conditions assigned were as follows: - LHS Constant head = 300 m RL - RHS Constant head = 240 m RL - Rainfall Recharge = 10% - Tunnel = Seepage review - Waiharakeke Stream = Seepage review The dual tunnel inflow model was assigned constant head conditions set at a ground elevation of 485 mRL to represent the highest head conditions along the alignment. Model Results The results of the surface effects model indicate no discernible loss of groundwater to surface waters would occur as a result of the tunnel. This assumes free draining conditions for a period of up to 30 days. In reality, any inflows from high permeability zones would be grouted of earlier than this or in advance of the tunnel actually reaching a structure.
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