Clay material can be considered as a collection of aggregates,which interact with each other mainly through mechanical forces.From this point of view,clay can be modeled by analogy to granular material.Then,an elastoplastic stress-strain relationship for clay was derived by using the granular mechanics approach developed in previous studies for sand.However,unlike sand,clay deformation is generated not only by the mobilizing but also by compressing aggregates.Thus,in addition to the Coulombs plastic shear sliding and a dilatancy type flow rule,a plastic normal deformation has been modeled for two aggregates in compression.The overall stress-strain relationship can then be obtained from the mobilization and compressing of aggregates through a static hypothesis of the macro-micro relations.