Microstructure and Permeability of Bentonite-Modified Loess after Wetting–Drying Cycles

Abstract

In this study, scanning electron microscopy, mercury intrusion porosimetry, and flexible-wall permeability tests were performed on the remolded loess (RL) and the 15% bentonite-modified loess (BML) after wetting–drying cycles. Crack propagation, microstructure damage, pore-size distribution, and saturated permeability were evaluated as a response to wetting–drying cycles. The cracks grow in three stages: crack initiation, rapid crack development, and attenuation. The loess is dominated by linked aerial pores and intergranular pores. With wetting–drying cycles, the number and diameter of intergranular pores grow, and additional aerial pores are generated from intergranular pores. When bentonite is added to the loess, the pore-size distribution curves shift from a trimodal to a bimodal shape. The porosity of samples grows in a declining increment that corresponds well to the increase in the permeability coefficient. Because of the swelling and filling effect of bentonite particles, as well as pore compression at higher confining pressures, the seepage channels are blocked. The permeability of BML after multiple wetting–drying cycles meets the antiseepage requirement of compacted clay liner of landfill that the permeability coefficient should be less than 10−9 m/s.