关键词: 软岩洞室, 广义SMP准则, 中间主应力, 最优支护力, 允许最大位移

Abstract: The existing optimal designs of tunnel support are all based on the Mohr-Coulomb (M-C) criterion, which cannot truly reflect the effect of the intermediate principal stress on rock strength and the three-dimensional unequal stress state of surrounding rock. Theoretical solutions for both the optimal support pressure of soft rock tunnel and the allowable maximum displacement of surrounding rock are derived based on the steady creep criterion expressed by the third invariant of deviatoric stress. The generalized spatially mobilized plane (SMP) criterion is employed to evaluate the strengthening effect of intermediate principal stress on rock strength. The obtained solutions in this study can be well generalized to the M-C criterion and the circumscribed Drucker-Prager (D-P) criterion, meanwhile they can be validated by an engineering instance. It is shown through parametric study that the differences among these three strength criteria actually reflect different considerations on the effect of the intermediate principal stress; the results of the M-C criterion and the circumscribed D-P criterion represent the two extremes, and then the results of the generalized SMP criterion is recommended; long-term rock strength is a key parameter for the optimal design of tunnel support, and the effects of surrounding rock cohesion and its internal friction angle are also significant, so that the rock strength parameters must be properly determined and their variabilities should be fully taken into account.

Key words: soft rock cavern, generalized SMP criterion, intermediate principal stress, optimal support pressure, allowable maximum displacement