Cyclic and Dynamic Behavior of Sand-Rubber and Clay-Rubber Mixtures

In this paper, the possibility of using fine scrap tyre rubber to improve the mechanical properties of soil subjected to cyclic loading is addressed. Ground rubber (0.1-0.8 mm) in various proportions (0, 9, 33% and 100% by weight) was mixed with a uniform river sand and a lean clay. Cyclic triaxial tests with bender elements were executed to observe the behaviour of the materials and also to determine damping and shear stiffness parameters. The results have shown that the addition of rubber has significantly decreased the density and shear stiffness of both types of soils, which favours mitigation of vibrations. The shear stiffness degradation at shear strains higher than 10(-3) was lower in specimens containing more rubber. Within this strain range, addition of rubber decreased the damping ratio, but increased the normalized accumulated absolute strain energy absorbed by the material. Higher rubber content in sandy specimens resulted in more elastic behaviour, with lower strain accumulation in each loading cycle, eventually resulting in a higher number of loading cycles before failure. The positive effect of rubber presence was not observed in compacted clay-rubber mixture, which sustained less loading cycles than clay alone. The influence of rubber addition in the p '-q stress space was expressed in the form of lower pore pressure generation which shifted the stress path further from the failure envelope.