Experimental and numerical study on homogenisation of BCV bentonite using dual density samples

Abstract

Homogenisation of bentonite materials is an essential feature for its sealing function in radioactive waste repositories. Presented study is focused on the laboratory investigation of the homogenisation of Czech BCV bentonite (Ca/Mg type). The experimental program included measurementof the swelling pressures of single-density and dual-density samples of the compacted bentonite, where dualdensity sample is composed of two layers compacted to two different dry densities. Tests were performed in constant volume cells, which allowed measurement of swelling pressure evolution. Dual-density tests included two identical samples saturated from different sides. Homogenisation was investigated through the determination of the final density distribution in a vertical profile from the post-mortem analysis. Further,the laboratory experiments were simulated by means of a thermo-hydro-mechanical hypoplastic model for bentonite implemented in the SIFEL coupled finite element code. It was found that swelling pressures developed by dual-density samples corresponded well to swelling pressures developed by single densitysamples of equivalent dry densities, while its time-evolution was different. Dual density samples also revealed very good level of density homogenisation after the test. The first observation (swelling pressure along with its temporal evolution) was predicted well by the model, which however underestimated the level of dry density homogenisation.