深埋隧洞开挖卸荷引起的围岩开裂特征及影响因素

通过理论分析和数值计算研究深埋地下隧洞开挖卸荷引起的围岩开裂，并分别对准静态和瞬态开挖缷荷引起的围岩开裂机制与开裂特征进行分析。采用双向受压条件下的压剪裂纹扩展模型和应力强度因子计算公式，分析了开挖面上岩体应力瞬态释放和围岩应力瞬态调整对围岩开裂过程的影响，并分别对准静态和瞬态卸荷引起的围岩开裂机制及影响因素进行探讨。研究结果表明，围岩开挖缷荷是深埋隧洞围岩发生开裂的重要原因之一，高地应力条件下围岩以剪切型断裂破坏为主；瞬态卸荷存在动态拉应力效应，开挖卸荷时间越短，引起的拉应力区及围岩开裂范围越大；围岩开裂深度及范围随着侧压力系数增加而增大，且开裂区近似成V型。深埋隧洞围岩开裂特征及影响因素研究，对进一步认识围岩开挖破坏的力学机制具有重要的意义。

Cracking characteristics and influential factors of surrounding rocks induced by excavation unloading in deep tunnel

Through the theoretical analysis and numerical calculation, cracking of surrounding rocks in deep tunnel induced by excavation unloading is studied. The cracking mechanisms and their characteristics of quasi-static and transient unloading under high in-situ stress are discussed respectively. For a case of deep circular tunnel the effect of this transient process on cracking of surrounding rocks is investigated by adopting an initiation model of crack under biaxial compression, and revised stress intensity factor is taken as cracking criterion. The analysis results show that the stress of unloading is a significant cause of surrounding rock cracking; the tensile stress zone exists under transient unloading; and the tensile stress plays an important role in the surrounding rock cracking under high in-situ stress; the less the duration of excavation unloading is, the larger the tensile zone and cracking range will be. The cracking depth and range increase with increasing lateral pressure coefficient; and the cracking region is approximately in V-shape. This study may be of great significance for further understanding the failure mechanism of surrounding rocks.