One of the critical problems in tunneling practices is the inflow of water into tunnels. The most significant difficulties resulted from water inflow to tunnels, include reduction of rock mass stability around the tunnel, the imposition of extra pressure on temporary and permanent supporting systems, and creating life and financial problems. Analytical and empirical methods by means of hydraulic analysis and regardless of existing discontinuities encounter great uncertainties in estimating the accurate groundwater inflow. Therefore, numerical models are preferred due to their capability in solving complex hydrogeological problems. The model dimension has an important role in the prediction of the inflow rate in numerical modeling. In other words, the distance between the model boundary and the tunnel border can greatly influence the inflow rate prediction. For example, if the distance is small, the inflow rate will be overestimated. Therefore, the objective of this study is to investigate the effect of model dimension on tunnel inflow assessment in numerical modeling. To this end, UDEC for DEM and Seep/W for FEM modeling were used and the impact of different model parameters, such as tunnel radius, joint spacing/equivalent permeability, horizontal and vertical model domain extent has been evaluated and the obtained results from each modeling method were compared together.

1. Introduction

One of the main hazards during tunnel construction is the water seepage into the tunnel which causes several problems in operation progress such as tunnel stability reduction, extra pressures on a support system, disastrous impact on environmental and geomaterial condition, deceleration in the implement operation, and finally, the emergence of financial issues. Due to the presence of complex geological variables and their effect on the water inflow into the tunnel, accurate prediction of seepage amount into the tunnel is very difficult (Cesano et al. 2003, Farhadian et al. 2012, 2013, 2017a, Butscher et al. 2017, Maleki et al. 2021).

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