A coupled fluid-mechanical interaction model for controlled gas migration mechanism by dilatancy effect in saturated bentonite

Abstract

A gas breakthrough in saturated bentonite is relevant to the safety of high-level radioactive waste repositories. The study of gas transport mechanisms in saturated bentonite is very important for the safety assessment of repositories. This paper proposed a coupled fluid-mechanical interaction model for predicting and simulating the path of gas transport and gas breakthrough in saturated Gaomiaozi bentonite. The model considered the effect of deformation and damage of bentonite on its permeability and introduced pore pressure into the deformation equation of bentonite. The damage coefficient was also introduced into the permeability evolution equation by combining the Mohr–Coulomb criterion, the maximum tensile stress criterion and the damage evolution. In addition, considering the heterogeneity of the soil, the Weibull distribution function was introduced to assign differential values to material parameters of the cells in the model. The numerical simulation of the bentonite stress field and seepage field was realized by the joint MATLAB and COMSOL secondary development, and the evolution law of the pore path in bentonite was explored under a flexible boundary. The gas breakthrough pressure and permeability pressures were calculated at various gas injection from a gas injection experiment into bentonite with flexible boundaries. Finally, the rationality and applicability of the model were verified by comparing the numerically calculated gas breakthrough pressure and permeability with experimental values.