管棚预支护条件下水下隧道开挖面三维稳定性分析

Three-Dimensional Face Stability Analysis of Underwater Tunnel with Pipe Roof Reinforcement

基于塑性极限分析理论,建立了考虑渗流力的管棚预支护条件下隧道开挖面三维稳定性分析模型,由此确定开挖面的极限支护压力。结合深圳地铁实际工程,采用该方法计算得到的开挖面极限支护压力与流固耦合数值计算结果吻合较好,验证了该方法的合理性,进而研究了管棚预支护对隧道开挖面渗流力的影响,分析了地下水位和管棚剩余长度与开挖面渗流力的关系。分析结果表明:渗流力对隧道开挖面稳定性有显著的影响,而且渗流力与地下水位呈线性关系,当隧道在富水地层施工时,必须考虑渗流力对隧道开挖面稳定性的影响;采用管棚预支护可以显著地减小隧道开挖面处的渗流力,但当开挖面前方管棚剩余长度超过2倍洞径时,再增加管棚长度对减小开挖面渗流力的效果不明显。

Based on the kinematic method of limit analysis, the three-dimensional model for expressing the face stability of underwater tunnel with pipe roof reinforcement is established. The proposed approach is employed to define the support pressure of tunnel face. For a certain tunnel excavation, the solutions computed by the proposed approach are compared with the results given by hydraulic-mechanical coupled analysis to verify the reasonability of the method. The proposed approach is also employed to study how the water level and length of pipe affect the seepage pressure. The analytical results reveal that the exist- ence of groundwater may seriously affect the face stability, and the linear formula is able to account for the influence of water level on seepage pressure. There is a relatively large reduction in the seepage pressure by adopting the pipe roof reinforcement technique. However, the studies also revealed that if the pipe length ahead tunnel face is longer than 2 times of tunnel diameter, the effect of pipe roof reinforcement on redu-cing seepage pressure is not significant.