Effect of Sand Particle Size on Hydraulic-Mechanical Behavior of Bentonite-Sand Mixtures

Bentonite-sand mixtures can be used as the base material of engineered barriers in deep high-level radioactive waste geological repositories. Swelling, compression, and permeability tests were conducted out on bentonite-sand mixtures with 30%, 50%, 70% and 85% sand content. Influence of sand content and particle size on the deformation and permeability characteristics of bentonite-sand mixtures were analyzed. The sand particle size affects the deformation characteristics by influencing the vertical stress required to form a sand skeleton, and the skeleton’s stability. When the sand content is less than the critical sand content, bentonite-sand mixtures cannot form a sand skeleton, and particle size has no effect on their characteristics. When the sand content is greater than the critical sand content and the vertical stress exceeds the initial deviation stress, a sand skeleton forms. In this case, smaller the sand particle size, lesser will be the vertical stress required to form a sand skeleton, and more the swelling of bentonite-sand mixtures. Further, more uniform particle size, more stable will be its structure and lesser the compressibility of bentonite-sand mixtures. The hydraulic conductivity is related to the flow area and the seepage path length, and particle size has no obvious effect on either with the same sand content. Therefore, the sand particle size has no obvious effect on mixtures’ permeability.