Abstract: Under the condition of no cubic strain, the loading-deformation relational expressions of wall rock are obtained according to simple loading characteristics of wall rock of tunnel. The relational expressions are simultaneously related with triaxial stress ( and ) and triaxial strain ( and ) in wall rock, and they are expressed by equivalent stress, , and equivalent strain, . The stress or strain state of elastic zone, hardening zone, softening zone and flowing zone of wall rock of tunnel are respectively corresponded with the stress or strain state of different stages of equivalent stress-strain curve, and they have strictly been demonstrated. Supposing equivalent stress, , and equivalent strain, , are regarded as middle variables, can the elastic and plastic analysis of surrounding rock be simplified, and can the calculation expression of deviatoric stress-strain energy generation of tunnel surrounding rock is written forthright. Equivalent shearing stress, , is the most shearing stress, , in wall rock. Equivalent shearing stress unit is acted on by the direct stress and shearing stress, but it only has shearing strain. This emphasizes an essence that the deformation and fracture of wall rock of tunnel are resulted from the most shearing stress and biased stress-strain energy. The determined slipping line based on equivalent shearing stress conception can be applied to strain hardening and softening stages of the materials and needn’t require the supposition condition of rigidity-plasticity.

Key words: simple loading, equivalent stress, equivalent strain, deviatoric stress-strain energy, slipping line