Study on analytical calculation method of water inflow in the tunnel of oblique crossing layered aquifer structure

Due to the complicated geological environment and karst hydrogeological conditions, water-inrush accidents often occur in the construction of tunnels in southwestern China. At present, there are many methods to predict tunnel water inflow, including analytic method and conventional hydrodynamic research method. There is a big discrepancy between calculated water inflow value and actual situation. Our research focused on the layered aquifer medium characteristics of water-bearing structure and movement characteristics. On the basis of existing tunnel gushing water inrush characteristics, the crossing relationships between tunnel and layered aquifer structure are divided into three categories, (I) tunnel longitudinal through layered aquifer structure, (II) tunnel through layered aquifer structure, and (III) tunnel obliquely crossing the layered aquifer structure. The revised formula of tunnel water inflow theory and experience in this study is inferred from steady-flow formula considering the boundary conditions. Inhomogeneous layered aquifer structure is considered as homogeneous structure, calculated by theory and experience formula. Next to the heterogeneity on one side of heterogeneity interface, the permeability coefficient of different strata can be fitted for a unified Kv; when crossing the layered water-bearing structure laterally, it is still calculated according to the original formula. When oblique crossing a layered water-bearing structure, the total flow rate is decomposed into two directions: transverse crossing and longitudinal crossing. The flow rates in the two directions are calculated respectively, and then superposed into the flow rates in oblique crossing.