Investigation of the swelling behaviour of compacted bentonite–sand mixture by mock-up tests

Two small-scale mock-up tests were carried out on a compacted mixture of bentonite and sand, one with saturation from the bottom only and the other with saturation from the top and bottom. Swelling pressure was monitored at different positions of the soil sample in both axial and radial directions. Results showed that the two-side saturation accelerates the swelling pressure kinetics by a factor of 4. The radial swelling pressure kinetics depends on the soil swelling, soil collapse, and interaction between the soil layers. Further analysis based on the relative humidity measurements in an infiltration test performed previously showed that the variations of swelling pressure with suction are similar to those found in literature, and that threshold points exist indicating the initiation of soil collapse. These threshold points appeared at higher suction when the soil was farther from the wetting face. The failure of the axial confining elements in the storage galleries was also simulated by releasing the piston and allowing a limited axial swelling of 20%. The radial swelling pressures decreased sharply upon the piston release and during the free axial swelling. A swelling pressure gradient was found from the bottom to the top with a higher value at the bottom. The density gradient was estimated based on the swelling pressure profile.