Swelling behavior of compacted bentonite with the presence of rock fracture

Abstract

In this study, the influence of rock fracture on the swelling behavior of compacted bentonite was investigated experimentally with bentonite compacted inside a hollow cylinder of fractured Beishan granite from China. During the test, hydration was allowed by letting water flowing into the compacted bentonite from the base plate, and air being expelled from the top plate. Along the sample, swelling pressure and relative humidity were monitored at different positions. Results showed that the presence of rock fracture significantly changed the hydration process of compacted bentonite. The evolutions of swelling pressure were directly related to the relative position to the rock fracture. At the same height, for the position closer to the rock fracture, a larger decrease in local dry density occurred, resulting in a larger loss in swelling pressure. This suggests that in field conditions of radioactive waste repository involving bentonite and rock, local filling of rock fracture by bentonite may occur, and the resulted bentonite swelling pressure decrease must be accounted for in the safety evaluation of the whole storage system.