穿越破碎带隧道掌子面力学模型及最小安全厚度研究

隧道穿越断层破碎带的稳定性及安全防护问题是目前隧道建设的难点。针对隧道掌子面前方存在破碎带松散岩土体的典型工况，基于隧道围岩以及掌子面的力学特性，采用理论计算、数值模拟、工程实践相结合的手段，提出了掌子面稳定岩体的最小安全厚度计算方法，并对隧道掌子面前方破碎带的预加固及处治方案进行了探讨。首先，建立了破碎带-岩板力学模型，将掌子面的岩体等效为受荷载作用的岩板，对受破碎带压力的岩板最小安全厚度展开计算分析，得到了岩板厚度与岩层倾角、破碎带有效高度的关系表达式，并对帷幕注浆处理参数进行了优化；随后基于理论计算结果，与某隧道穿越破碎带施工中因未控制掌子面岩体厚度而导致隧道失稳的典型案例展开对比分析；最后结合Comsol Multiphysics软件开展数值仿真模拟，分析了不同岩层倾角、隧道埋深、注浆预处理参数等因素对掌子面岩板最小安全厚度的影响。结果表明：理论计算、工程实际与数值模拟结果具有较好的一致性；正常施工时掌子面最小安全岩板厚度随破碎带有效高度的增大而增大，随岩层倾角增大而减小，故应在达到安全厚度之前对破碎带进行预支护；在选用帷幕注浆方法对破碎带进行预处理时，最小安全岩板厚度随着岩层倾角的增大而减小，此时在注浆过程中需要保留较大的安全厚度，同时控制注浆压力。

Mechanics Model to Determine the Minimum Safe Thickness of Tunnel-face Rock Slab at a Fracture Zone

The stability and safety of tunnels passing through fault fracture zones are the difficulties in tunnel construction today. Typical working conditions in fracture zones with loose soil masses are constraints in tunnel construction. Considering these conditions and the mechanical properties of surrounding rock, and using theoretical calculation, numerical simulation, and engineering practices, a method to calculate the minimum safe thickness of tunnel-face rock for rock mass stability was developed. Further, fracture zone pre-reinforcement and suitable treatment schemes were explored in this study. First, a fracture zone-rock slab mechanics model was established, in which the rock mass equivalent for rock slab loads was the constraint. This model calculated the pressure on a fracture zone due to rock slab minimum safe thickness and obtained an effective equation for the calculation of the relationship between rock slab thickness, strata dip angle, and fracture zone height. Further, the curtain grouting processing parameters were optimized in this model. Then, based on the results of this theoretical analysis, a comparison was done between a typical case of construction of a tunnel through an unstable fracture zone where the thickness of the rock mass on the tunnel-face was not controlled and one where the thickness was controlled. Finally, the Comsol Multiphysics software was used to perform numerical simulations, and the effects of various rock dips, tunnel depths, and grouting pretreatment parameters on the minimum safe thickness of a tunnel-face rock slab were analyzed. The results show that:the results of the theoretical calculation, engineering practice, and numerical simulation are in good agreement. During normal construction, the minimum safe rock slab thickness of the tunnel face increases with increase in the effective height of the crushing zone and decreases with increase in the dip angle of the rock layer. When the curtain grouting method is used for pretreatment of the fracture zone, the minimum safe rock slab thickness decreases with increase in the rock dip angle. Thus, large minimum safe thicknesses should be reserved in the grouting process while controlling the grouting pressure.