Abstract: Surrounding rock energy is released in company with tunnel excavation; and in the meantime deviatoric stress is brought in surrounding rock. Surrounding rock stress is the superposition of stress in virgin rock mass and deviatoric stress. The deviatoric stress or its strain energy dominates the breakage of rock mass. On condition that the hydrostatic pressure and the volumetric strain of rock mass is equal to zero, by using the stress distribution expressions of surrounding rock which are educed on base of the constitutive model that its elastic and nonlinear softening segment linked glossily in paper [1], and using multiple integral, the strain energy of deviatoric stress, , is calculated in the elastic and softened zones of surrounding rock. It is proved that can be deduced concisely by way of integrating the ground stress with respect to the displacement of tunnel wall , and multiplying by perimeter of tunnel wall, and the principle of the calculation approach of is expatiated. The energy released by surrounding rock in the process of tunnel excavation is equal to the product of perimeter of tunnel wall and the integral of the surrounding rock pressure with respect to . Thereby, the circumstances of deviatoric stress energy and the released elastic energy in surrounding rock in response to can be expressed by the geometrical form that the area enclosed by the curves - and - . The acquired findings can deepen the understanding of mechanical response of surrounding rock owing to tunnel excavation and operating condition of surrounding rock after tunnel excavation.

Key words: tunnel, displacement of tunnel wall, surrounding rock pressure, energy release of surrounding rock, strain energy of deviatoric stress