Water inflow forecasting for tunnel considering nonlinear variation of permeability coefficient

To assess the water inflow which is more suitable to the actual conditions of tunnel, an empirical correlation about the permeability coefficient changing with depth is introduced. Supposing that the surrounding rock is heterogeneous isotropy, the formula for calculating water inflow of tunnel with the nonlinear variation of permeability coefficient is deduced. By the contrast analysis with the existing formulas, the presented method has the similar value to them; moreover, the presented method has more simple form and easy to use. Due to parameter analysis, the water inflow decreases after considering the nonlinear variation of permeability coefficient. When the attenuation coefficient a>0, the water inflow increases first till reaches the maximum at a certain depth, then decreases and is close to 0 finally if deep enough. Thus, it is better to keep away from the certain depth where it is with the maximum water inflow for safe operation and economical construction, and reduce the water damage. Based on the analysis, the radius of tunnel has less impact on the amount of water inflow, and the water inflow just increases by 6.7% when the radius of tunnel increases by 1 m.