上覆流沙层隧道开挖面稳定性分析与数值试验研究

为解决上覆流沙层隧道开挖面极易发生坍塌破坏的技术难题，以典型该地质条件下的青岛地铁M2号线啤苗区间（啤酒城站至苗岭路站）为研究对象，基于开挖面的实际破坏特征建立了开挖面失稳破坏力学模型，从功能转化平衡角度，进行了隧道开挖面稳定性上限分析，并利用强度折减与重力加载两种方式，提出了隧道开挖面安全系数，得到了不同开挖面土体黏聚力、摩擦角、重度、隔水层厚度及隧道开挖高度下的临界土体破裂范围及破裂模式。理论研究表明：随着开挖面土体黏聚力、摩擦角、隔水层厚度等参数的增加，开挖面安全系数不断增大，稳定性不断提高；随着土体重度、隧道开挖高度增加，开挖面安全系数不断减小，稳定性不断降低。通过建立不同工况的数值模型验证了理论研究的正确性，得到了上覆流沙层地质条件下开挖面的典型破坏模式和临界参数，并提出了相应工程建议。研究成果为青岛地铁M2号线的顺利贯通及该类地质条件下的隧道施工提供了理论指导和科学对策。

Stability analysis and numerical experiment study of excavation face for tunnels overlaid by quicksand stratum

In order to resolve the technical problem of tunnel face collapse in the tunnel which is overlaid by quicksand stratum, a typical tunnel below the dynamic water-rich and weakened sand stratum of Qingdao metro No.2 line (the section of Pi-Miao), was taken as a research model, and a failure mechanical model was established according to the actual destructive characteristics. Based on transformation equilibrium from work to energy, the upper bound analysis of tunnel face stability was conducted. By the upper bound analysis and the strength reduction/gravity loading method, the tunnel face safety factor was obtained, and the critical soil rupture range given different soil cohesions, frictional angles, densities, water-resisting layer thicknesses and tunnel excavation heights were obtained as well. The theoretical research showed that tunnel face safety factor increased and stability was enhanced with the increase of cohesion, frictional angle and water-resisting layer thickness, and safety factor and face stability decreased with the increase of density and tunnel excavation height. A series of numerical calculation models was established to verify the accuracy of theoretical research, which obtained typical failure modes and critical parameters of tunnel face overlaid by quicksand stratum. Results from this research provide theoretical guidance and scientific solutions to the transfixion of Qingdao No.2 metro line and other cases with similar geological conditions.