Considering the unloading stress due to excavation at the bottom and sides of a foundation pit and the shielding effect of the retaining structure at the bottom,a semi-analytical and semi-empirical method is proposed based on the Mindlin formula.A calculation formula for the displacement of an existing metro tunnel caused by ex-cavation of an adjacent foundation pit is deduced,and effects of the foundation pit size,change of relative position to the tunnel and reinforcement measures on existing metro tunnel displacements are analyzed.Results show that the horizontal and vertical displacements of a tunnel increase with an increase of the tunnel overburden, and the dis-placement increases obviously with a decrease of the clear distance between the foundation pit and the tunnel.In-creasing the excavation length of the foundation pit has little effect on tunnel displacement, while the excavation width and depth of the foundation pit have an obvious effect on tunnel displacement.Finally,the effect of reinforce-ment and control measures could be considered;and the maximum horizontal displacement of the tunnel decreases linearly with a decrease of the stress loss ratio of the retaining structure of the foundation pit,but the vertical dis-placement of the tunnel hardly changes.%文章考虑基坑坑底和侧壁的开挖卸荷应力以及坑底围护结构的遮拦效应,基于Mindlin位移解公式,提出了一种半解析半经验解方法,推导得到了基坑开挖引起邻近既有隧道位移的计算公式,分析了基坑尺寸、与隧道相对位置的改变以及加固控制措施对既有地铁隧道位移的影响.研究结果表明:隧道的水平和竖向位移随着隧道埋深的加大而有所增加;随着基坑与隧道净距的减小,隧道位移则明显增大;基坑开挖长度的增加对隧道位移影响较小,而基坑开挖宽度和开挖深度会对隧道位移产生明显影响;该方法可以考虑加固控制措施的效果,随着基坑围护结构应力损失率的减小,隧道最大水平位移呈线性减小,但隧道竖向位移变化不大.
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