Three-dimensional monotonic and cyclic behavior of a gravel-steel interface from large-scale simple-shear tests

Gravel-structure interfaces are involved in many large-scale geotechnical applications and play a vital role in the performance of soil-structure interaction systems. A large-scale simple-shear device was professionally developed and used to investigate three-dimensional (3-D) monotonic and cyclic shear behavior of a gravel-steel interface in two-way beeline, cross, and circular shear paths. The soil deformation was measured and was used to determine the interface thickness. The deforming and sliding displacements of the interface were quantified and separated from the total tangential displacement. Results show that the interface thickness is about 6-7 times the mean grain size, D-50, independent of the normal stress and shear path. Under 3-D loading conditions, the shear stress vs. tangential displacement hysteretic response exhibits notably 3-D features. The interface becomes stiffer because of the hardening behavior of the gravel during cyclic shearing. The total normal displacement can be divided into irreversible and reversible components, which present different responses. The peak shear strength is mobilized when the interface dilatancy rate reaches the maximum at a sliding displacement of about 0.5D(50), and behaves in an anisotropic manner caused by the shear orientation effect. The normal stress and shear paths have significant influences on the 3-D interface behavior.