The monotonic and cyclic behavior of the interfacebetween structure and coarse grained soil was investigated through teststudy in both macroscopic and microscopic way. The internal relationshipbetween micro-physical state change and macro-mechanical response isdiscovered through analyzing the observationresults of the interface. The concept of damage is therefore extended tocharacterize the evolution of the physical states as well as resultingevolution of the behavior of the interface between structure and coarsegrained soil, which develops continuously from the initial state to theultimate state. The evolution of the physical statesmainly consists of the crushing and compression of soil particles near thestructure. The volumetric strain due to dilatancy of the interface could bedivided into reversible and irreversible dilatancy component, in which theirreversible dilatancy component could essentially indicate the evolution ofthe physical states as well as the behavior of the interface. Theirreversible volumetric strain due to dilatancy is then demonstrated as ameasurement of the damage extent of the interface, which could be normalizedas damage variable. Finally, a new scheme is presented to constitute adamage model of the interface between structure and coarse grained soil.