基坑开挖引起下卧既有隧道变形的简化计算方法

Simplified Method for Evaluating Deformation of Adjacent Existing Tunnel Induced by Foundation-Pit-Excavation

为得到基坑开挖对邻近下卧既有隧道变形受力影响,提出一种可预测基坑开挖对下卧隧道竖向变形影响的简化计算方法。采用Mindlin解获得基坑开挖引起既有隧道轴线处的附加应力,将隧道假定成无限长Euler-Bernoulli梁搁置在Vlasov地基;引入隧道侧向土体的影响,考虑既有隧道两端约束,进一步得到隧道竖向变形差分解。工程案例研究表明:与既有文献中有限元数据和实测数据对比,验证了该方法计算结果的合理性;与将隧道搁置在Vlasov地基模型(EB-V模型)和Winkler(EB-W模型)地基模型的解析计算结果比较,本文方法计算结果更贴近实测数据。进一步参数研究表明:隧道与基坑中心间距、隧道埋深以及土体模量的增大会引起隧道竖向变形及内力减小;随着既有隧道抗弯刚度逐渐增大,隧道竖向变形会逐渐减小,但会引起既有隧道内力增大。

To obtain the deformation and stress of existing tunnel due to adjacent foundation pit excavation above,a simplified method for predicting the influence of the excavation on the existing tunnel is presented.Additional stress at axis of existing tunnel caused by excavation can be calculated by Mindlin solution.The tunnel is assumed as Euler-Bernoulli beam laying on the Vlasov foundation and the influence of the lateral soil of the tunnel is introduced.Considering the constraints at the two ends of tunnel,difference decomposition of vertical deformation of existing tunnel can be obtained.The engineering case study shows that compared with the finite element method and the measurement in the existing literature,the feasibility of the calculation results of the presented method is confirmed.Compared with the analytical calculation results of the tunnel resisting on the Vlasov foundation model(EB-V model)and the Winkler foundation model(EB-W model),the presented method is in line with measurement.Further investigation indicates that the increment of the distance between tunnel and excavation center,the tunnel buried depth and the soil modulus will result in the reduction of the vertical deformation and internal force of the tunnel.With the increasing of tunnel bending stiffness,tunnel vertical deformation will decrease gradually,but the tunnel internal force will increase.