Swelling characteristics of compacted bentonite with gaps filling by sands

Gaps, also known as technical voids, are considered inevitable during the installation of bentonite buffer material in the deep geological disposal project. The presence of the gaps is a matter of concern because it may lead to the outflow of buffer material. As a countermeasure, the use of sands to fill the gaps are considered. To investigate the effect of gap filling sands on the swelling characteristics of bentonite, one-dimensional swelling pressure tests were conducted on specimens composed of a compacted bentonite layer, and sand layer in which water was infiltrated from the sand. Three silica sands (V3, V5, V7) with different median particle sizes ( D 50 = 1.3, 0.58, 0.16 mm) were used, and the sand layer was made of different dry densities ( ρ ds ). The slice in which the penetration could be observed was cut out, and the penetration thickness ( H p ) and penetrated bentonite mass ( M pb ) was obtained. Gap filling sands were found to have significant effects on the first peak pressure ( p p1 ), while it had insignificant effects on the valley pressure ( p v ) and equilibrium pressure ( p eq ). H p and M pb were found to be strongly influenced by D 50 and ρ ds , showing positive correlations with D 50 and negative correlations with ρ ds . With the results, the effects of gap filling sands to p p1 , p v , p eq and the penetration were discussed.