Rock is characterised as the elastoplastic coupling

which means its elastic parameters change with the variation of plastic deformation beyond the threshold of yield. Based on current classification

definition and constitutive function of strain

the following work was conducted under the framework of elastoplastic coupling. Firstly

through compressive tests

the evolution of elastic parameters was analysed from the aspects of the damage and plastic deformation. The strain was mainly studied under the condition of loading incremental step. It was suggested that the strain increment corresponding to the loading increment could be decomposed into elastic strain increment

elastic strain increment and plastic strain increment respectively. Furthermore

was following the generalised Hooke’s law

while was against Hooke’s law. The elastic relationship was constituted with elastic parameters after loading incremental step. Constitutive functions were then formulated in strain and stress spaces under loading

neutral loading and unloading conditions

respectively. The discussion was made on the internal variable increment reflecting the microstructure change. In general

the classification and definition of strain are explicit in concept and suitable for strain hardening and softening sections. Moreover

the elastoplastic coupling constitutive function considers the influences of different loading conditions on the changing rates of elastic parameters. Overall

the strain definition and constitutive function are in accordance with rock elastoplastic coupling characters.