Experimental study of swelling characteristics of bentonite-sand mixture

A series of experimental researches of swelling pressure and swelling strain of bentonite-sand mixture are conducted by using self-developed swelling apparatus. Based on the experimental data obtained, the relationships between swelling pressure and time, vertical and horizontal swelling pressures, swelling strain and time, and swelling strain and water-absorbing volume are analyzed. The results show that the maximum swelling pressure and the maximum swelling strain of bentonite-sand mixture depend on the initial dry density and bentonite content of mixture, and increase with the increasing of these two factors. The increase of the dry density results in the decrease of the ratio of horizontal and vertical swelling pressures, and a linear relationship can be obtained between them. For bentonite-sand mixture with different bentonite contents, a hyperbolic relationship is obtained between swelling strain and time, and an approximate S-curve relationship is obtained between swelling strain and water-absorbing volume. Furthermore, the maximum swelling strain and bentonite content of bentonite-sand mixture demonstrate an exponential relationship. The experimental results are of reference value for design of buffer and back-filling materials in high-level radioactive repositories.