Modelling of tunnel inflow with combination of discrete fractures and continuum

Abstract

Fitting a water inflow into excavations can provide model parameters of the water flow and transport. The combination of 2D discrete fractures and 3D equivalent continuum is a suitable tool for an inhomogeneity modeling without an excessive computational effort. We demonstrate a tunnel inflow fitting with the combination of fractures and continuum on two examples of a field measurement. The problem dealt here is also an adjustment of 3D discretization onto a complex of subdomains cut by discrete fractures and a tunnel. We had to make a compromise between the geometrical accuracy and the mesh size but we kept the model problem relevant to real conditions and we concerned both the geometry and the calculated water inflow at the same time. We used the software Flow123D (which had been developed at our institute) which is based on the mixed-hybrid finite element method applied onto the multidimensional model the numerical scheme that is convenient for the velocity/flux field evaluation together with a mass balance and also a connection between discrete unknowns of 1D, 2D, and 3D subdomains.