Numerical study on 3D water-air two-phase seepage characteristics of undisturbed granite residual soil at REV scale

Abstract

To reveal the dynamic seepage mechanism of water-gas two-phase in soil, the undisturbed granite residual soil in Fuzhou was selected as the research object. Based on the computer tomography(CT) image and AVIZO-COMSOL interactive docking technology, the Level Set method was used to study the 3D water-gas two-phase seepage characteristics of the undisturbed granite residual soil at the REV scale. The results show that the residual gas in the pores is mainly distributed in blocks on the pore edges, dead corners and sudden changes of pore throats. Among the numerous pores of the REV model, there are only a few major seepage pores, which are generally characterized by wide and straight pores. In different seepage stages, the velocity distribution is different. In general, the flow velocity increases first, then decreases, and then gradually increases. The maximum velocity growth rate and decrease rate are 61.04% and 40.60%. With the increase of seepage time, the saturation of the water phase shows a sharp upward trend, and the saturation of the gas phase shows a sharp downward trend, they both occur in the initial stage of seepage, and then gradually tend to be stable. Finally, the saturation of the water phase and the residual gas phase tend to 91.86% and 8.14% respectively.