Role of Tangential Displacement Amplitude in 3D Cyclic Simple Shear Behavior of Gravel–Steel Interface

The tangential displacement amplitude determines the mobilization of shear strength and the deforming and sliding displacements of soil–structure interfaces, and therefore plays a crucial role in the interface behavior. A series of three-dimensional (3D) simple-shear interface tests were conducted between gravel and steel to investigate the influence of tangential displacement amplitude on the tangential deformation, volumetric change, and shear strength. Test results show that deforming and sliding displacements are distinctly induced by shearing. The deforming displacement migrates toward the initial shear direction, caused by the shear orientation effect, and the migration becomes magnified and then stabilizes with cyclic shearing. The shear strength would not be mobilized when the tangential displacement amplitude is relatively small. It behaves in an anisotropic manner if mobilized and gradually degrades as cyclic shearing continues, attributed to the dominant particle crushing over the shear densification effect. Two critical tangential displacement amplitudes are found for the mobilization of shear strength, and determine whether the shear strength could be mobilized during cyclic shearing and whether it is immediately mobilized at initial shearing, respectively. The tangential displacement amplitude primarily affects deforming and sliding amplitudes and their migration, shear stiffness, irreversible and peak reversible normal displacements, peak and residual cyclic shear strength, and anisotropy extent, instead of their relationship patterns. An increased tangential displacement amplitude results in magnified sliding amplitude, decreased deforming weight, accelerated degradation of deforming amplitude, and magnified migration of deforming and sliding displacements. Additionally, large tangential displacement amplitude leads to large irreversible and peak reversible normal displacements, small shear stiffness, and small peak and residual cyclic shear strength. The peak reversible normal displacement is determined by and has a linear relationship with the deforming displacement, and the irreversible normal displacement presents perfect consistency behavior against shear work density, regardless of tangential displacement amplitude. The consistency behavior could be well described using a hyperbolic model, which significantly simplifies the 3D constitutive modeling of the interface.