Abstract: Systematic tests were conducted to investigate constitutive rule of the interface between structure and coarse grained soil. Based on macro- and micro-observation, five essential constitutive rules could be induced to characterize the monotonic and cyclic behavior of such interface. The constitutive rules includes: (1) the shear strength is nearly proportional to normal stress; (2) the shear stress would increase and tend to a stable value with the development of shear strain due to a monotonic stress path application under constant normal stress condition; (3) the volumetric strain due to dilatancy is composed of a reversible and an irreversible dilatancy component. The reversible dilatancy component obviously exhibits anisotropical behavior. The shear strain component related to the volumetric strain due to dilatancy exhibits a variable proportion in total shear strain during shear application; (4) the compressibility decreases with the increase of normal stress; (5) the physical state and mechanical behavior evolve and tend to be stable during shear application.