Depending on the frequency, type and number of cycles of the loads emanating from earthquakes, machine foundations or ocean waves, special testing devices capable of controlling stress or strain are needed for the determination of relevant engineering parameters at the geosynthetic interface for design. A multipurpose large size direct shear test device has been developed capable of applying monotonic and cyclic loads both with stress and strain control. An upper box of 300 mm width and 300 mm length slides over the lower box with 900 mm length. The normal stress on the upper box is applied by pneumatic rubber muscle actuators attached to sliding cars moving on rails placed parallel to the bottom box. This way the normality of the force is always sustained even under large horizontal displacements. Strain control is provided by a linear actuator driven by a step motor. The stress control is achieved by antagonistic pneumatic rubber muscle actuators which can apply monotonic and cyclic stress at the interface. The interface behavior of crushed stone and a smooth and a textured geomembrane is investigated under low normal stress and large horizontal displacement. The large dimensions of the box allowed testing of the crushed stone with its actual size which is very critical for the stress concentrations. A special film was used to map the stress distribution at the the interface of crushed stone and the two membranes. At large horizontal displacements, the interface shear strength of the smooth geomembrane increased slightly.
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