地应力方向对地下隧道围岩破坏特征的影响

Influence of in Situ Stress Direction on the Failure Characteristics of Surrounding Rock of Underground Tunnels

地应力方向是影响地下隧道围岩破坏特性的重要因素。为研究地应力方向对地下隧道破坏特征的影响以及硬岩隧道周围板裂破坏的形成机制,首先对含有倒U形孔洞的花岗岩试样进行了一系列单轴压缩试验。然后利用颗粒流程序(PFC)建立了二维数值模型,进一步研究孔洞的主应力方向和高宽比对双轴压缩下试样断裂特性的影响。结果表明:孔洞的存在会显著降低花岗岩试样的单轴抗压强度和弹性模量;当最大主应力的方向与孔洞直边墙平行或成小角度时,孔洞直边墙上会出现明显的板裂破坏,表明在这种情况下,地下隧道直边墙应采用更坚固的支护结构。此外,孔洞高宽比越大,板裂破坏越明显,岩石损伤也越严重。

The direction of in situ stress is an important factor influencing the failure characteristics of the surrounding rock of underground tunnels.In this study,to investigate the influence of the principal stress direction on the fracture characteristics of underground tunnels and the formation mechanism of spalling failure around hard rock tunnels,a series of uniaxial compression tests were first carried out on granite specimens containing an inverted U-shaped cavity.Then,a two-dimensional numerical model was constructed by particle flow code(PFC)to further investigate the influence of the principal stress direction and aspect ratio of the cavity on the fracture characteristics of the specimens under biaxial compression.The results show that the uniaxial compressive strength and elastic modulus of granite specimens with an inverted U-shaped cavity are significantly lower than those of the intact specimen.When the direction of the maximum principal stress is parallel to or at a small angle to the straight sidewall of the cavity,obvious spalling failure occurs at the cavity’s straight sidewall,indicating that stronger support structures should be applied to the straight sidewalls of underground tunnels in this situation.Moreover,the specimens containing a cavity with a larger aspect ratio show more obvious spalling failure and experience more severe damage.