A comparative study on evaluation of steady-state groundwater inflow into a circular shallow tunnel

The objective of this study is to make a comparison among different methods used for evaluation of steady state groundwater inflow to a shallow circular cross section tunnel. These methods include: analytical solutions, empirical methods and numerical modelling. Analytical formulas provide an estimation of inflow rate based on some simplifying assumptions which are somehow unrealistic. Therefore, their results are over/underestimated. Empirical methods are presented based on the experiences of different tunnel projects and they mostly provide an appropriate qualitative estimation; while, their quantitative predictions are not desirable. Despite analytical and empirical approaches, numerical modelling is a suitable tool for solving complex geomechanical and hydrogeological conditions. Hence, their results are more reliable and precise for designation of efficient drainage systems. In this study, groundwater inflow into Tabriz Metro-Line 2 (TML2) is evaluated by means of these methods and their results were compared. The results indicated that all of the methods provide consistent results, however, it is inferred that in the absence of sufficient data, Raymer equation can provide more reliable estimation of inflow rate for shallow tunnels in comparison to other analytical and empirical solutions due to its higher correlation with numerical results.