The cyclic simple-shear behavior of soil-structure interfaces under different normal stresses is of great significance in theoretical analysis and engineering practices. A series of interface tests between gravel and steel was conducted under different normal stresses using a 3D large-scale simple-shear apparatus

and the influence of normal stress on the cyclic simple-shear behavior of the interface was explored in detail. The normal stress plays a crucial role in the magnitudes of the shear behavior of the interface

including deforming and sliding displacements

shear stress

reversible and irreversible normal displacement

and cyclic shear strength

while it has slight influence on the relationship pattern of shear behavior. Increased normal stress leads to increased deforming displacement at the first few shear cycles

accelerated reduction and decreased stabilized amplitude of deforming displacement. Enhanced normal stress also results in increased shear modulus

decreased shear modulus coefficient at the first few shear cycles

increased stabilized shear stress and cyclic shear strength of the interface. In addition

larger normal stress results in larger irreversible normal displacement

smaller peak reversible normal displacement

smaller transition tangential displacement and transition stress ratio of the interface. The cyclic shear strength behaves well in accordance with Mohr-Coulomb criteria

regardless of normal stress. Perfect consistency exists in the stress ratio versus tangential displacement response and irreversible normal displacement versus shear work density response

independent of normal stress

and can be described using hyperbolic models. These consistency characteristics will significantly simplify the constitutive modelling of soil-structure interfaces.