The effects of technological voids on the hydro-mechanical behaviour of compacted bentonite-sand mixture

International audienceCompacted bentonite-based materials are often used as buffer materials in radioactive waste disposal. A good understanding of their hydro-mechanical behaviour is essential to ensure the disposal safety. In this study, a mixture of MX80 bentonite and sand was characterized in the laboratory in terms of water retention property, swelling pressure, compressibility and hydraulic conductivity. The effects of the technological voids or the voids inside the soil were investigated. The technological voids are referred to as the macro-pores related to different interfaces involving the buffer material, whereas the voids inside the soil is referred to as the common macro-pores within the compacted bentonite/sand mixture. The results obtained show that at high suctions, the amount of water absorbed in the soil depends solely on suction, whereas at low suctions it depends on both suction and bentonite void ratio. There is a unique relationship between the swelling pressure and the bentonite void ratio, regardless of the sample nature (homogeneous or not) and sand fraction. However, at the same bentonite void ratio, a higher hydraulic conductivity was obtained on the samples with technological voids. The effect of sand fraction was evidenced in the mechanical yield behaviour: at the same bentonite void ratio, the bentonite-sand mixture yielded at a higher pre-consolidation stress