超大断面分岔隧道施工力学特性模拟及监测分析

Simulation and Monitoring Analysis of Mechanical Characteristics of a Super-large Cross-section Bifurcated Tunnel During Construction

采用数值模拟与现场监测相结合的方式,结合工程实例,分析了超大断面隧道围岩应力分布的特点及施工力学特性。研究结果表明Ⅲ级围岩超大断面隧道单侧壁导坑法开挖时,受拉破坏区域均存在于台阶处,上部导坑掌子面未发生受拉破坏,塑性破坏分布于开挖台阶两侧;上部导坑若一次性开挖,面积过大,掌子面出现较大范围塑性屈服破坏区域,需采用上下台阶法开挖上部导坑。本文工程隧道拱顶最大下沉量、钢拱架所受最大拉应力和最大压应力、拱顶处围岩压力均处于安全状态;现场监测与数值模拟计算结果较为吻合,验证了超大断面隧道采用单侧壁上下导洞法开挖的安全可行性。

In this paper,methods of numerical simulation and on-site monitoring are used to analyze the stress distribution and mechanical characteristics of surrounding rock during construction of an actual super-large cross-section tunnel.The study results show that when the single-side guide pit method is used to excavate a tunnel in grade Ⅲ surrounding rock,there is a tensile failure zone at the step,and no tensile failure occurs at the upper guide tunnel face,and the plastic failure is distributed on both sides of the excavation step.If the upper guide pit is excavated at one time and the area is too large,there will be an area of plastic yielding failure at the tunnel face.Thus,the upper guide pit needs to be excavated by the upper and lower steps method.The maximum settlement of the tunnel vault,the maximum tensile stress and compressive stress of the steel arch,and the surrounding rock pressure at the vault are all in a safe state.The field monitoring results are consistent with the numerical simulation results,which verifies the safety and feasibility of the single-side upper and lower pilot tunnel method to excavate the super-large cross-section bifurcated tunnels.