Effect of pore water chemistry on the behaviour of a kaolin–bentonite mixture during drying and wetting cycles

The behaviour of a kaolin–bentonite mixture with different pore water chemistry, i.e. distilled water, NaCl and CaCl2 solutions, was investigated through a number of cyclic drying and wetting tests. Experimental tests were carried out on compacted samples of the expansive soil (i.e. mixture of 80% kaolin and 20% bentonite) in a modified oedometer with different pore water chemistry under a surcharge pressure of 10 kPa. The vertical and radial deformations of the samples were determined during different stages of drying and wetting. In addition, the soil–water characteristic curve was established by the filter paper technique for samples with different pore water chemistry. The results indicate that the shrinking–swelling deformation was nearly the same when the equilibrium condition was attained. Furthermore, the paths of drying and wetting converged to an S-shaped curve at equilibrium condition. This curve consists of one linear and two curvilinear portions, and the majority of the deformation occurred in the linear section. The hysteresis phenomenon was also studied through the void ratio and suction, and the results indicated that the hysteresis is gradually diminished with increasing the number of drying and wetting cycles