Applied with a new professional apparatus

the 3D cycle mechanical behavior of a gravel-structure interface is investigated considering initial static shear stress. The tangential displacement in the direction of initial static shear stress is obviously observed due to the cyclic shear application; it has a linear relationship with its perpendicular shear distance. The angle between the line and the initial static shear stress behaves in quadratic polynomial manner with initial static shear stress level. The magnitude of initial static shear stress has little influence on the shear strength and the relation pattern between tangential shear stress and strain

but has significant effect on the peak perpendicular shear stress

volumetric change and the relationship between volumetric change and tangential displacement of the interface. As the initial static shear stress increases

the peak perpendicular shear stress and the corresponding tangential displacement of the interface decrease

the interface becomes more hardened due to cyclic shear application

and dilates more at the beginning of shear application while less during subsequent cyclic shearing.