基于统一强度理论和稳定蠕变准则的软岩巷道最优支护

巷道最优支护可以实现新奥法安全经济的最佳支护状态，本文根据软岩流变控制原则和统一强度理论，合理考虑中间主应力与强度准则选取的影响，推导两种稳定蠕变准则下巷道最优支护力和围岩允许最大位移的理论解答，给出公式适用条件、应用步骤，并进行两个工程实例验证，分析中间主应力、岩石长期强度以及围岩抗剪强度参数等对巷道最优支护力与围岩允许最大位移的影响规律。研究结果表明：本文理论解答可退化为文献已有结果，具有较好的可比性；所得公式表达简洁、参数易于确定，具有良好的工程应用前景；两种稳定蠕变准则的巷道最优支护参数的变化规律一致且整体差异较小，但应力偏张量第三不变量准则相应解答的适用范围更广；中间主应力效应和强度准则选取对巷道最优支护参数的影响显著，Mohr-Coulomb准则的结果过于保守，难以发挥围岩的强度潜力；岩石长期强度是巷道最优支护设计的关键参数，围岩黏聚力相比内摩擦角对巷道最优支护参数的影响更为明显，应充分考虑岩石强度参数的变异性。所得结果可为软岩巷道的最优支护设计与施工提供理论指导和建议。

Optimal Support in Soft Rock Tunnel Based on the Unified Strength Theory and Steady Creep Guideline

The optimal support of tunnel could achieve the best supporting state with both safety and economy as suggested by New Austrian Tunnelling Method (NATM). Theoretical solutions for the optimal support pressure of tunnel and the allowable maximum displacement of surrounding rock under two steady creep guidelines were presented on the basis of the controlling principle of soft rock rheology. The unified strength theory was adopted to reasonably consider the influences of intermediate principal stress and choosing strength criteria. Then, the applicable conditions and application steps about the proposed solutions were provided. Finally, these theoretical solutions were validated by two engineering cases, and the influences of a wide range of variation of parameters like intermediate principal stress, long-term strength of rock as well as shear strength of surrounding rock have been discussed on the optimal support pressure of tunnel and the allowable maximum displacement of surrounding rock. It is found that: the obtained theoretical solutions in this study have good comparability and can degenerate into the available results from the literature; the expressions of the obtained theoretical solutions are concise, and more the parameters involved are easy to been determined, thus the proposed theoretical solutions have a good prospect of engineering applications; generally speaking, the optimal parameters of tunnel support under two steady creep guidelines change similarly and have litter differences, however the result according to the third invariant guideline of deviator stress tensor has broader applicable scope; the influences of intermediate principal stress and choosing strength criteria on the optimal parameters of tunnel support are significant, and the result of Mohr-Coulomb criterion is too conservative to make use of potential rock strength; long-term strength of rock is a key parameter for the optimal design of tunnel support, and the influence of surrounding rock cohesion is more pronounced compared to its internal friction angle, therefore it should take full account of the variability of rock strength parameters. The obtained results can provide a theoretical guidance to the design and construction of the optimal support in soft rock tunnel.