Effects of rubber content on macro- and meso-scopic shear characteristics of geogrid-rubber sand interface

A large-scale direct shear apparatus is used to study the interface shear properties of the geogrid-reinforced rubber-sand mixture. The variations of shear stress with shear displacement and volume deformation characteristics are analyzed under different rubber contents, relative densities and normal stresses. Based on the indoor experiments, direct shear models for sand and rubber-sand mixture on PFC^3D are established to reveal the meso-mechanical mechanism of geogrid-reinforced rubber-sand mixture in the direct shear process. The results show that the shear strength of rubber-sand mixture rises first and then drops with the increase of rubber content under the same compaction. The optimal rubber content is 10%. The looser the mixture is, the greater the difference is in shear strength (|τ₀-τ₅₀|) caused by the rubber content. Adding some rubber particles in sand can increase its apparent cohesion and interface friction angle, but the shear strength is mainly affected by the latter. The relative thickness of the shear band becomes smaller in view of the entry of rubber particles. The rubber particles inhibit the rotation of the sand particles, making the porosity change of the rubber-sand mixture smaller than that of the sand. The fabric distribution of the rubber-sand mixture can reflect the distribution of contact force, and the number of touch points among particles is a little more than that of the sand. The normal contact force and tangential contact force of the mixture are smaller than those of sand. The addition of rubber particles increases the damping energy consumption of the system and improves the elasticity of the mixture.