A new combined analytical-numerical method for evaluating the inflow rate into a tunnel excavated in a fractured rock mass

Abstract

Abstract A new method combining analytical and numerical tools is developed for evaluating the inflow rate to an underground tunnel that is excavated in a fractured rock mass. The method is comprised of a series of analytical formulas based on Darcy's and Cubic laws and assumes the rock mass to be impermeable except for the discontinuities which are considered to be the main pathways for groundwater flow. The geometrical and spatial characteristics of the discontinuities, the depth of the tunnel below the water table and the dimension and orientation of the tunnel are the effective parameters for calculating the groundwater inflow rate. The proposed method includes a new semi-numerical equation developed to determine the hydraulic gradient at the wall of the tunnel, using empirical input parameters derived from numerical simulations. The inflow rate to the tunnel is calculated from the general expression of Darcy's law, using the hydraulic conductivity calculated using the Cubic law and factoring the hydraulic gradient defined by a newly developed equation, taking into account the pertinent flow surface. In order to determine the inflow rate using this proposed method, the data required are the orientation, hydraulic aperture and spacing of the joint sets, the level of the water table, and the depth and diameter of the tunnel.