岩溶隧道断续节理掌子面突水判据及灾变过程

为了给岩溶区隧道掌子面突水灾害的预警与防治提供理论支持，针对岩溶隧道掌子面断续节理防突岩体，从断裂力学角度分析了地应力和岩溶水压力等自然营造力作用下断续裂纹的压剪起裂属性以及分支裂纹尖端应力强度因子随水压和支裂纹扩展长度的变化规律，推导了断续节理岩体发生轴向张拉贯通破坏突水的临界水压力。运用两带理论和推导的临界水压力公式，建立了基于最小安全厚度的岩溶隧道掌子面断续节理防突层失稳突水判据，并分析了掌子面前伏岩溶水压力、断续主裂纹长度、断续裂纹排距及裂纹与最大主应力夹角等对防突层最小安全厚度的影响规律。采用可考虑流固耦合效应和岩体结构特征的三维离散元数值分析方法，研究了岩溶隧道近接前方高压富水溶腔顺序开挖中掌子面防突层岩体位移场、渗流场等演化规律及其临突特征。数值模拟结果表明：随着岩溶掌子面的不断推进，掌子面防突层岩体挤出位移逐渐由单一卸荷引起向卸荷和前伏岩溶水压共同影响过渡；掌子面各测点位移及位移增加幅度均持续增大；掌子面挤出位移和掌子面水流速度在突水通道即将形成时出现激增和突升现象，具有明显的突水前兆特征。

Water Inrush Criterion and Catastrophe Process of a Karst Tunnel Face with Non-persistent Joints

This study aims to provide theoretical support for early warning and prevention for water inrush of a karst tunnel face. As to the water-resistant rock mass with non-persistent joints ahead of a karst tunnel face, the compressive shear cracking property of non-persistent cracks and the changing law of stress intensity factor at the branch crack tip with water pressure and its extended length were analyzed under karst water pressure and geo-stress from the perspective of fracture mechanics. The critical water pressure of a rock mass with non-persistent joints under axis-tension coalescence mode was deduced. The water inrush and instability criterion of water-resistant strata with non-persistent joints ahead of a karst tunnel face, based on the minimum safety thickness, was established by using the two-band theory and the deduced formula of critical water pressure. The influence of the karst water pressure, length of non-persistent cracks, array pitch of non-persistent cracks, and angle between the crack and the maximum principal stress on the minimum safe thickness of water-resistant strata was discussed. A 3D DEM, considering the fluid-solid coupling effect and structural characteristics of the rock mass, was adopted to study the evolution rule of displacement and seepage fields in the water-resistant rock mass ahead of the tunnel face. The precursory features in sequential excavation of the tunnel working face close to the high pressurized karst cave before it. Based on the results of numerical simulation, the transition from the single effect of unloading on the extrusion displacement of the karst tunnel face to the combined action of unloading and karst water pressure occurs when the karst tunnel face advances. The displacement and its amplitude at each measuring point in the water-resistant strata continue to increase in the excavation process. The extrusion displacement and water flow velocity in the tunnel face suddenly increase when the water inrush pathway is about to form, and this is important precursory information for preventing a water inrush disaster.