基坑群开挖引起邻近隧道附加应力研究

Study on Additional Stress of Adjacent Tunnel Caused by Excavation of Foundation Pit Group

基坑开挖卸载会导致邻近地铁隧道产生附加应力,附加应力过大时会造成隧道失稳,进而影响地铁运营安全。为了研究基坑群开挖引起邻近隧道附加应力变化规律,首先利用Mindlin理论解推导所得的隧道附加应力计算公式,然后依托杭州某邻近地铁隧道的基坑群开挖工程对所推导的公式进行验证。在此基础上分析了隧道埋深、隧道-基坑水平距离、隧道-基坑夹角3个因素对附加应力分布规律的影响。根据不同埋深、不同隧道-基坑水平距离下计算结果,结合规范对群坑开挖产生的危险区域进行了划分。结果表明:(1)随着隧道埋深增加,其竖向附加应力会逐渐增大,水平附加应力会逐渐减小,竖向、水平附加应力均会随隧道-基坑水平距离增加而减小;(2)基坑群开挖时,随着隧道-基坑水平距离增加,埋深对于竖向附加应力影响系数逐渐减小,对于水平附加应力影响系数会出现先减小后增加的趋势;(3)竖向、水平附加应力随着隧道-基坑夹角增加而增大,隧道所受附加应力主要由与其距离最近的基坑开挖产生;(4)随着隧道-基坑距离增加,群坑开挖时竖向附加应力减小率比单个基坑开挖时小,水平附加应力减小率与单个基坑开挖相比会有所增加。

Excavation unloading of foundation pit will lead to additional stress in adjacent subway tunnels.Excessive additional stress will cause instability of subway tunnel,and then affect the safety of subway operation.In order to study the influence law of additional stress on tunnels,the calculation formula of tunnel additional stress caused by foundation pit excavation is derived by using Mindlin theoretical solution and is verified based on the excavation project of a foundation pit group near a subway tunnel in Hangzhou.Then,the influence of three factors,including tunnel depth,horizontal distance between tunnel and foundation pit,and angle between tunnel and foundation pit,on additional stress in tunnel is analyzed.The research results show that:(1) with the increase of tunnel depth,the vertical additional stress of tunnel increase while the horizontal additional stress decrease,and the vertical and horizontal additional stress will decrease with the increase of the horizontal distance between tunnel axis and foundation pit;(2) during excavation of foundation pits,with the increase of horizontal distance between tunnel and foundation pit,the influence coefficient of tunnel depth on vertical additional stress decreases gradually,while the influence coefficient of tunnel depth on horizontal additional stress decreases first and then increases;(3) the vertical and horizontal additional stresses increase with the increase of the angle between tunnel axis and foundation axis,and the additional stress of the tunnel is mainly caused by excavation of the foundation pit which is the closest;(4) with the increase of the distance between tunnel axis and foundation pit axis,the reduction rate of vertical additional stress caused by pit group excavation is smaller than that caused by single pit excavation,while the reduction rate of horizontal additional stress caused by pit group excavation is larger than that caused by single pit excavation.