盾构下穿北京地下国铁直径线分阶段变形响应分析

Stage Deformation Response Analysis of Shield Tunneling through Beijing Underground National Railway Line

盾构穿越既有隧道的施工风险控制一直是城市地铁建设面临的难题也是研究的热点。针对盾构下穿既有大直径隧道工程施工风险控制难题,以北京地铁8号线王府井站—前门站区间盾构下穿国铁直径线为工程背景,建立了三维数值模型,采用FLAC3D有限元差分软件进行计算,并将既有隧道的变形分为5个阶段,对每个阶段的沉降影响进行了评估,最后将模拟数据与实测数据进行对比分析,以此验证该模型的有效性。研究结果表明:不同下穿阶段中,阶段3对既有隧道变形影响最为显著,受刀盘开挖、盾体通过、盾尾脱出三重因素的影响,该阶段内既有隧道的沉降占比最大;竖直方向上,既有隧道拱顶呈“V”型沉降槽,拱底呈“W”型沉降槽;水平方向上,下穿段正上方既有隧道发生向隧道内侧收敛的现象,并距新建隧道轴线越远,收敛现象逐渐减弱。

The risk control of shield tunnel through existing tunnels has always been a difficult problem and research hotspots in urban subway construction.In view of construction risk control problems during the shield tunnel crossing the existing large diameter tunnel engineering,the shield tunnel from Wangfujing Station to Qianmen Station of Beijing metro line 8 crossing Beijing Underground National Railway Line is taken as the engineering background.A3D numerical model is established and calculated by FLAC3D differential software.The deformation of the existing tunnel is divided into five stages.The settlement influence of each stage is evaluated.Finally,the results are compared with the measured data to verify the validity of the model.The results show that stage 3 has the most significant influence on the deformation of the existing tunnel,and the settlement ratio is the largest due to three factors of cutter head excavation,shield body passing and shield tail protrusion.In the vertical direction,the existing tunnel vault is V-shaped settlement groove,the arch bottom is W-shaped;In the horizontal direction,the existing tunnel directly above the down-crossing section converges towards the inside of the tunnel,and the further away it is from the axis of the new tunnel,the weaker the convergence.