Numerical analysis of steady-state groundwater inflow into Tabriz line 2 metro tunnel, northwestern Iran, with special consideration of model dimensions

In order to prevent problems like casualties, delays in tunneling procedure, and increasing tunneling costs, predicting groundwater inflow into tunnels and designing an efficient drainage system are necessary. Several analytical solutions exist in the literature, but they cannot accurately estimate groundwater inflow due to simplifying assumptions. Numerical methods, however, are increasingly used to predict groundwater inflow with higher accuracy. This study is aimed at predicting the steady state groundwater ingress into Tabriz line 2 metro tunnel (TML2: a shallow urban tunnel) by considering model dimensions as critical factors in the numerical analysis process. A 2-D numerical finite element analysis of steady state groundwater inflow was performed along the tunnel based on geological and geotechnical investigations. Water inflow into TML2 was then estimated based on optimum model dimensions. The total amount of groundwater inflow into TML2 was estimated to be 7013.6 l/min. The maximum cumulative water inflow into the tunnel was also predicted to occur between 15.55 and 16.25 km in the tunnel with a 4754 l/min inflow rate, which demands an effective drainage program. Finally, for validation of the methodology groundwater inflow values obtained through 2D finite element analysis were compared to those calculated with a well-known inflow evaluation method (Raymer solution).