Shear wave velocity in sand-rubber mixtures from bender element tests

Scrap tyre rubber alone and/or mixed with sand makes an effective and sustainable material that can be used in geotechnical seismic isolation systems to mitigate vibrations. Sand, rubber and sand-rubber mixtures containing 1/3, 1/2 and 2/3 rubber content by volume were investigated in this study. A series of bender element tests under triaxial stress conditions were carried out to assess shear wave velocity in these materials. Different approaches to determining the appropriate travel time have been considered. The frequency at which the shear wave velocities using the start-to-start and peak-to-peak approaches are equal yields values that satisfy available recommendations and are in very good agreement with the results of our own resonant column tests on the same type of material. The test series with various sequences of loading/unloading/reloading showed that an increase in the overconsolidation ratio from 1 to 8.5 causes a negligible change in the shear wave velocity of up to 5% in sand and rubber, and a decrease by 10% to 15% in sand-rubber mixtures. Equations describing the relations between the shear wave velocity, confining stress and rubber content, which can be used in practice, are derived.