Research on gas migration properties in a saturated bentonite/sand mixture under flexible boundary conditions

Gas migration/breakthrough in saturated bentonite is an important issue for the evolution of the sealing ability of the engineered barrier in deep geological repositories. The main contribution of our study is to provide insights into the water and gas transport properties in a compacted bentonite/sand mixture, which was wrapped by a flexible Viton™ membrane directly before being put into a triaxial cell. The experimental results indicate that the water permeability is very low and the magnitude is in the order of 10−20 m2. Gas breakthrough tests show that no continuous gas flow was detected during the entire gas breakthrough test (until the gas pressure of 10 MPa), which indicates that the compacted bentonite/sand mixture has a good sealing ability after full saturation. Another important finding is that the gas migration properties are closely related to the stress state around the sample, the internal pore fluid pressure, and the creep effects caused by the two factors.