A Quantitative Criterion-based Methodology for Selecting Appropriate Domain Size for Numerical Modeling of Groundwater Inflow into Tunnel

Selecting the appropriate model size is a challenging issue in the numerical modelling of groundwater inflow into underground excavation. This issue was studied in this paper by presenting a methodology for selecting appropriate domain size for numerical modeling of groundwater inflow into tunnel that is excavated inside of semi-infinite aquifer. To reach this goal, first, a dimensionless factor, so-called normalized rate of inflow variation (NRIV), was defined in cooperation with its limit value, so-called acceptable level of variation (ALV). Then, the appropriate or suitable domain size (SDS) of numerical model was determined based on the NRIV and ALV. The applicability of suggested methodology was evaluated for the results of wide range geometrical parameter of tunnel (including different tunnel radiuses and depths) and different flow domain sizes. The results of this study indicate that the required domain size for numerical modelling of groundwater inflow into tunnel increase nonlinearly for larger and deeper tunnels. Moreover, the required domain size increases to 1.8 times by decreasing the level of ALV from 0.0005 to 0.0001, where the relative accuracy of results has only increased up to 4%. Since the larger domain size requires much computational difficulties and insignificant accuracy, the ALV in the level of 0.0005 is suggested for practical numerical modelling of groundwater inflow into tunnels.