城市地铁盾构施工地层变形三维数值模拟分析

Three-dimensional Numerical Simulation Analysis of Stratum Deformation Induced by Subway Shield Construction

富水砂层条件下,盾构施工问题多、风险大、施工变形难控制。以南昌地铁某区间盾构隧道工程为研究背景,采用有限差分软件FLAC3D建立了三维盾构施工力学模型,对富水砂层条件下的盾构施工过程进行动态数值模拟,并结合现场实测数据分析了盾构施工引起的地表沉降规律。结果表明:盾构施工引起的横向地表沉降呈"V"形,最大地表沉降发生在隧道中心正上方,最终形成的沉降槽宽度约为6倍隧道外径;盾构施工引起的纵向地表沉降呈"S"形,盾构开挖面前方表现为隆起,开挖面后表现为沉降,在开挖面后一定距离逐渐趋于稳定;开挖面支护力对稳定开挖面土体及减小地表沉降有较大影响;盾构进洞与出洞施工中存在较大风险,应采取相应的工程措施以保证盾构施工安全进行。所得结论可供南昌地铁区间盾构隧道设计与施工参考。

There are many problems,great danger,and great difficulty in controlling deformation when constructing a shield tunnel in water-rich sandy stratum.On the basis of a case study of the shield tunnel of Nanchang Subway,adopting the finite difference software（FDM）FLAC to establish three-dimensional mechanical model to simulate the dynamic process of shield construction in water-rich sandy stratum condition and combining with the actual measurement date,we analyzed the ground settlement caused by shield tunnel construction.The analysis results indicate that transversal ground settlement induced by shield construction was assumed as a V-shaped curve,the location of maximum ground settlement was situated above the tunnel center,and the width of the settlement tank was about 6D.Longitudinal ground settlement induced by shield construction was assumed as an S-shaped curve.The ground in front of the excavation surface uplifted and behind excavation surface settled.The ground deformation behind excavation surface decreases gradually with the increase of distance from the excavation surface.The supporting force has significant influence on soil stability on excavation surface and ground settlement reduction.There are high risks when the shield settles in and draw out.So we should take corresponding measures in practical engineering to ensure construction safety.The conclusion can provide useful reference for design and construction of subway tunnels in Nanchang.