Combination of water head control and axis translation techniques in new unsaturated cyclic simple shear tests

A cyclic simple shear device was modified for testing coarse-grained soils at unsaturated conditions. A combined methodology of controlling suction for the practical range of coarse-grained soil water retention curves was adopted. Water head control method was used to accurately control suction within capillary and transition zones of such soils. The axis translation technique, on the other hand, was employed as a complementary approach to reach higher suction values within residual zone. In order to evaluate the performance of the new setup, independent cyclic tests were carried out at various initial suctions including all key points and zones along the primary drying path. The analyses of cyclic stress-strain curves revealed an S-shaped trend of shear modulus against suction, where the peak occurs after residual suction. The merit and necessity of recent modifications were highlighted through comparing shear modulus obtained from constant-suction tests with that of constant-water content experiments.