Experimental study on the 1-D free swelling of compacted bentonite

Abstract

This paper presents a new designed 1-D free swelling test of compacted bentonite in glass tubes to simulate the process by which the bentonite cushion in the nuclear waste disposal reservoir swells and squeezes into the crack after absorbing the fissure water from surrounding rock. Deionized water and NaCl, Na2SO4, CaCl2 solutions with different concentrations were used as soaking solutions, and the change of the specimen height with time was recorded until the swelling completed. The effects of initial dry density, initial water content, and soaking solution concentration and type on the swelling deformation of bentonite were analyzed. Results show that the maximum swelling strain, almost independent from initial water content, increases with the initial dry density. The increase in the concentration of the salt solution reduces the free swelling deformation, and the degree of inhibition is related to the type of the salt solution. The effect of the concentration and type of the salt solution on swelling property can be uniformly reflected by the osmotic suction that acts as an additional stress applied on bentonite and is quantified as osmotic pressure item of the total effective stress proposed previously that controls the swelling strain of compacted bentonite. Then, the maximum swelling strains of the compacted bentonite under different soaking solutions in 1-D free swelling test can be predicted by a uniform power-law relationship with the total effective stress.