基于Hoek-Brown准则的隧道围岩改进单元安全度分析

为了建立基于应变软化Hoek-Brown强度准则的围岩安全性评价方法，首先推导了Hoek-Brown准则与Mohr-Coulomb准则之间的关系，求得等效内摩擦角和黏聚力。其次将屈服接近度和破坏接近度进行变换统一到单元安全度量体系，进而总结了由Hoek-Brown应变软化参数表征的改进单元安全度（Zone Safety Index，ZSI）公式，实现了对单元的弹性、屈服和破坏状态的表达，并基于FLAC3D中FISH语言进行二次开发，编译了ZSI计算程序。随后，通过FLAC3D软件建立三维隧道模型，对该方法进行验证，并研究了Hoek-Brown准则参数对ZSI的影响规律。最后针对甄峰岭隧道大变形段的锚杆加固效果进行研究，利用ZSI法对大变形段不同长度锚杆加固方案进行安全稳定性对比分析，确定了较为合理的加固支护措施。研究结果表明：①ZSI小于1的区域与MIDAS的有效塑性应变区域基本一致，验证了ZSI程序的正确性，且ZSI可对岩体的弹性、屈服、破坏区域进行量化评价。②ZSI随地质强度指标GSI增加而增大，采用三次多项式进行拟合精度较高；随着单轴抗压强度σ_ci增大，ZSI呈指数方程增加，具有较高的相关性，扰动越大，单元安全度越小，表征围岩稳定性越差，ZSI随扰动因数D呈双曲线递减趋势变化；③ZSI法能够作为隧道初期支护方案优化和安全性评价的参考指标，对相关隧道的优化结果显示，3 m长注浆锚杆，同时加强其他支护结构能有效控制事故区的大变形，且安全性较好。

Analysis of Improved Zone Safety Index of Tunnel Surrounding Rock Based on Hoek-Brown Criterion

To establish a safety evaluation method for surrounding rock based on the strain-softening Hoek-Brown strength criterion, the relationship between the Hoek-Brown criterion and Mohr-Coulomb criterion was derived and the equivalent internal friction angle and cohesion force were obtained. Then, the yield approach index and the failure approach index were transformed into a unit safety evaluation system. Furthermore, the ZSI (Zone Safety Index) formula characterized by Hoek-Brown's strain-softening parameters was summarized; the expressions of the elasticity, yielding, and destruction of the unit were realized; the FLAC3D FISH language was redeveloped, and the ZSI calculation program was compiled. Subsequently, a three-dimensional tunnel model was established by FLAC3D software and the method was verified. The influence of Hoek-Brown criterion parameters on ZSI was also studied. Finally, the bolt reinforcement effect of the large deformation section of the Zhenfengling tunnel was studied. The ZSI method was used to compare the strengthening effect of the bolts with different lengths in the large deformation section and reasonable reinforcement measures were determined. The results show that:① The areas of ZSI less than 1 is essentially consistent with the effective plastic strain zone in MIDAS, which verifies the correctness of the ZSI program. Furthermore, ZSI can quantitatively evaluate the elastic, yielding, and failure regions of the rock mass; ② ZSI increases with increasing GSI and the cubic polynomial is used for higher fitting accuracy. As σ_ci increases, ZSI increases exponentially with a high correlation; the larger the disturbance, the smaller the unit safety and the worse the stability of surrounding rock is characterized. The ZSI changes with the hyperbolic curve of D; ③ The ZSI method can be used as a reference index for the optimization and safety evaluation of the initial support scheme of the tunnel. For the specific tunnel study, the optimization results show that the 3 m long grouting anchor and other supporting structures can effectively control the large deformation of the accident area, thus improving safety.