Characterization of a soil-rough structure interface using direct shear tests with varying cyclic amplitude and loading sequences under a large cyclic testing cycle condition

This paper aims to investigate the effects of cyclic shear amplitudes and loading sequences on a soil–structure interface using direct shear tests under a large number of loading cycles. A series of cyclic direct shear tests were performed on a granular soil-rough interface under the constant normal load (CNL) condition. Initially, monotonic interface direct shear tests were carried out as benchmarks to specify test boundaries and proper ranges of assigned cyclic amplitudes. Dry standard Fontainebleau sand in dense and loose conditions and a modified rough surface material were utilized to represent a soil-rough structure interface. A series of CNL cyclic interface direct shear tests was then conducted by varying the applied cyclic shear stress amplitudes and the cyclic loading sequence (small-to-large and large-to-small patterns) with a large number of testing cycles (104). Immediately after the cyclic shear tests were completed, monotonic interface direct shear tests were again performed to examine the post-cyclic behaviour of the soil-rough interface. Test results yielded that the applied cyclic shear stress amplitudes did affect the soil-rough interface by inducing a gradual contraction and an expansion in shear displacement accumulation. The maximum stress ratio could notably influence the volumetric behaviour and shear displacements. The accumulation of mean cyclic displacements was independent of the change in cyclic shear stress amplitudes between two consecutive cyclic loading sequences. The post-cyclic behaviour showed that changing the shear stress cycles between two consecutive packages did not influence the peak stress ratio.