富水砂层大断面暗挖隧道施工地层演化

对于施工环境复杂的暗挖隧道工程,科学合理掌握施工地层演化过程是安全施工的前提.以北京地铁12号线光熙门站—西坝河站区间富水砂层大断面暗挖隧道工程为研究背景,借助FLAC3D有限差分软件,对工程设计施工方案进行模拟,得到了施工过程中地层孔隙水压力、地层沉降损失演化过程,并与现场监测数据进行对比验证,为工程施工规避风险源提供参考.结果 表明:施工掌子面孔隙水压力集中位置主要在暗挖隧道上方注浆形成的"注浆拱"拱顶以及断面未注浆范围;隧道施工过程中,沿施工掘进方向在施工掌子面前、后10 m到掌子面位置范围内,是发生涌水关键位置;地层沉降值经历了由沿中轴线对称分布到集中在中轴线位置处的变化过程,最后沉降值沿中轴线对称分布,导洞1施工掌子面处地表沉降值稳定在12 mm左右;初期支护拱顶沉降以及拱脚水平收敛均分别在45、30 d达到稳定;现场反馈的施工信息与模型计算地层演化过程相吻合,计算结果可为富水砂层大断面暗挖隧道施工方案的选择提供参考.

Study on the Stratigraphic Evolution of Large Section Bored Tunnel Construction in Water-rich Sand Layers

Under the condition of complex construction environment, it is the premise of safe construction to scientifically and reasonably grasp the evolution process of construction strata for the subsurface excavation tunnel. In this paper, Guangximen Station to Xiba River Station of Beijing Metro Line 12 was taken as the research background. According to the Finite difference software FLAC 3D, the engineering design and construction scheme was simulated. Specifically, the evolution process of formation pore water pressure and formation settlement loss during construction was obtained. Moreover, the simulation data and on-site monitoring data were used for comparative verification, providing a reference for engineering construction to avoid risk sources. The results show that: 1) The pore water pressure on the tunnel heading is mainly concentrated in the " grouting arch " vault above the dark excavation tunnel and the ungrouting range of the section. Besides, during tunnel construction, the key position of water gushing appears in 10 m in front of or behind the tunnel heading along the construction tunnelling direction; 2) The settlement value of formation changes from symmetrical distribution along the central axis to concentrated at the central axis position, and Finally, the settlement value has been symmetrically distributed along the central axis, and the final settlement value is symmetrically distributed along the central axis. Additionally, the surface subsidence value at tunnel heading in pilot tunnel 1 is stable about 12 mm. The settlement of arch roof and the horizontal convergence of arch foot are stable in 45 days and 30 days respectively. 3) The construction information of field feedback is consistent with the model calculation of formation evolution, and the calculation results can provide references for selection of the construction scheme of large section subsurface excavation tunnel in water rich sand layer.