Cyclic behavior of gravel-steel interface under varying rotational shear paths

Cyclic rotational behavior of a soil-structure interface is imperative for understanding the three-dimensional behavior; this requires testing the interface under systematically varying rotational shear paths. A series of cyclic tests were conducted on the gravel-steel interface along linear, elliptical, and circular shear paths by systematically varying the orthogonal amplitude shear displacement ratio. The resultant peak shear stress was observed to be independent of the shear direction and dependent on the shear path. The interface demonstrates a coupling response among the orthogonal shear directions during the rotational shear, which governs the three-dimensional shear mechanism. Owing to such coupling, during the cyclic shear, the unloading extent from the resultant peak loading state at different quarters of a shear cycle diminishes as the shear path changes toward a circle; this leads to the monotonous shear proceeding in a circular route with an insignificant change in the shear direction. Significant dilatancy is induced by rotational shear, which can be divided into irreversible and reversible components. The final compression of the irreversible dilatancy increases as the area under the rotational shear path increases. The reversible dilatancy diminishes as the shear path becomes a circle. The interface evenly demonstrates aeolotropy under the rotational shear condition.