隐伏溶洞影响下隧道开挖稳定性数值模拟

隐伏溶洞是引起隧道围岩失稳甚至塌方的常见不良地质之一,为分析其对隧道开挖稳定性的影响,采用FLAC3D有限差分法和现场监测手段,探讨了隐伏溶洞尺寸、溶洞与隧道净距及溶洞位置对隧道开挖过程中围岩应力场、应变场及隧道变形的影响规律。研究表明：①围岩最大剪应力与最大剪应变增量均随溶洞尺寸增大而增大（随净距增大而减小）,塑性区集中于隧道-溶洞中间岩柱;②隧道变形时程曲线呈“S”形,隧道变形随溶洞尺寸增大而增大（随净距增大而减小）;③当溶洞直径大于0.6倍隧道宽度,且与隧道净距小于0.6倍隧道宽度时,隐伏溶洞对围岩塑性区和隧道变形具有明显影响,且隧道侧部溶洞对隧道稳定性最为不利;④建议岩溶隧道工程采用动态化设计、施工及监测,并采用综合超前地质预报探明实时地质情况。

Numerical Analysis on Influence of Concealed Karst Cave on Tunnel Excavation Stability

Concealed karst cave is one of the common harmful geology which causes the instability and even collapse of tunnel surrounding rock. To analyze the influence of concealed karst cave on the stability of tunnel excavation, the influence of the size of the concealed karst cave, the net cave-tunnel distance, and the location of the karst cave on the stress field, strain field and deformation of the surrounding rock during tunnel excavation was discussed using FLAC3D finite difference method and field monitoring method. Research shows that: (1) Both the maximum shear stress and the maximum shear strain increment increase with the increase of the cave size (decrease with the increase of the net cave-tunnel distance), and the plastic zone concentrates on the rock pillar between the tunnel and karst cave. (2) The time history curve of tunnel deformation is in the shape of "S". The tunnel deformation increase with the increase of cave size (decrease with the increase of net distance). (3) When the diameter of the cave is greater than 0.6 times the tunnel width, and the net distance is less than 0.6 times the tunnel width, the concealed cave has obvious influence on the plastic zone of surrounding rock and the tunnel deformation. Furthermore, the karst cave lateral to the tunnel has the most unfavorable effect on the tunnel stability. (4) It is suggested that dynamic design, construction and monitoring should be adopted in karst tunnel engineering, and comprehensive advanced geological prediction should be adopted to explore the real-time geological conditions.