Набухание и проницаемость компактированных бентонитов при высоком солесодержании в условиях изменения давления раствора

Abstract

This study presents results of two series of permeameter experiments with 15 bentonites compacted to a bulk density of 1.6 g/cm3 before and after one-year contact with a model clay porewater with a salinity of 155 g/l. For four original bentonites, a double-peak pattern of swelling pressure evolution was revealed, which was observed previously only at much lower salinities. For 80 % of bentonites, swelling pressure and permeability were in the range of 0.8—4.8 MPa and 7·10−20—3·10−18 m2 (for original ones) as well as 0.5—2.2 MPa and 4·10−19—6·10−18 m² (for ones after one-year contact). A fl uid pressure surge of 12.6 MPa caused no hydraulic fracturing of original bentonites. This observation challenges the validity of threshold values of a few MPa for onset of hydraulic fracturing in compacted bentonites proposed earlier using an alternative experimental method. Yet, this fl uid pressure surge and a moderate one of 0.3 MPa caused a decrease of swelling pressure by up to 66 % — an effect, which need to be accounted for when designing and assessing the performance of bentonite-based barriers in a geological repository.