A sand-rubber deformable granular layer as a low-cost seismic isolation strategy in developing countries: Experimental investigation

This paper presents experimental investigations on the feasibility of using a sand-rubber deformable granular layer as a low-cost seismic isolation strategy for developing countries. The mechanical characteristics of a potential failure mechanism inside the sand-rubber layer are investigated. Direct shear testing is performed to quantify the angle of friction of three different sand-rubber mixtures subjected to different vertical stress levels. The experimentally derived mechanical characteristics are compared to the corresponding values for pure rubber and pure sand samples. The frictional characteristics of sliding between a sand-rubber layer and a timber interface are identified. Direct shear testing is performed to quantify the quasi-static friction of the same sand rubber mixtures against a timber interface, that is part of the foundation casting, subjected to alternative vertical stresses. The effect of the shear rate and the saturation of the sand-rubber mixture on the aforementioned mechanical characteristics is presented. A uniaxial shaking table experimental setup is used for the investigation of the dynamics of a rigid sliding block and the quantification of the kinetic friction of different sliding interfaces against two different sand-rubber mixtures for two different sand-rubber layer heights. The rigid sliding block designed to slide against the sand-rubber layer is subjected to both a harmonic ramp loading and earthquake ground motion excitation. The design outcome of this static and dynamic experimental investigation is the determination of the optimum grain size ratio and the height of the sand-rubber layer, that corresponds to the lower (and more favourable from a seismic isolation view point) friction coefficient between the sand-rubber layer and the foundation. The quantification of these fundamental parameters paves the way for a holistic design of a response modification strategy for mitigating seismic damage in developing countries.