This paper investigates tunnel face stability in soft rock masses via coupled limit and reliability analyses. Specifically, a 3D face collapse mechanism was first constructed. Then the Hoek–Brown failure criterion was introduced into the limit analysis via the tangential technique. Taking the variability of rock mass parameters and loads into consideration, a reliability model was established. The collapse pressure and failure range of tunnel faces were determined. In addition, the required factor of safety (FS) and supporting pressure under three safety levels were obtained, and the corresponding safety level graphs for support design were presented. Comparison of the obtained results with previous work demonstrates the rationality of the 3D collapse mechanism and the validity of the results. A decrease in the geological strength index, Hoek–Brown parameter m_i, and uniaxial compressive strength or an increase in the disturbance factor results in a nonlinear increase of the collapse pressure and an enlargement of the failure zone. Such changes also lead to a nonlinear increase of the required support pressure under a certain safety level. By contrast, the FS does not exhibit any obvious change when these parameters vary. Therefore, when a rock mass is of poor quality or heavily disturbed, the advance support should be enlarged from upper front to right above the tunnel face. Moreover, as the safety level increases, both the required FS and supporting pressure of the tunnel face increase nonlinearly at a higher rate.

中文翻译：

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基于Hoek-Brown破坏准则的软岩体三维隧道面稳定性概率分析

本文通过耦合极限和可靠度分析研究了软岩体中的隧道面稳定性。具体而言，首先构造了3D人脸塌陷机制。然后，通过切线技术将Hoek-Brown破坏准则引入极限分析。考虑岩体参数和载荷的变化性，建立了可靠性模型。确定了隧道工作面的坍塌压力和破坏范围。此外，还获得了三个安全等级下的所需安全系数（FS）和支撑压力，并给出了相应的支撑设计安全等级图。将获得的结果与以前的工作进行比较，证明了3D塌陷机制的合理性和结果的有效性。地质强度指数下降，中号_我，和单轴抗压强度或坍塌压力的非线性增加和故障区的放大的增加干扰因素的结果。这种变化还导致在一定的安全水平下所需支撑压力的非线性增加。相反，当这些参数变化时，FS不会显示任何明显的变化。因此，当岩体质量较差或受到严重干扰时，应从隧道的前上方到右上方扩大前进支护。此外，随着安全等级的提高，所需的FS和隧道面的支撑压力都以较高的速率非线性增加。