邻近基坑开挖引起既有隧道的纵向变形响应

Analytical solution for evaluating deformation response of existing metro tunnel due to excavation of adjacent foundation pit

基坑开挖将会对隧道周围土体造成扰动,进而导致隧道结构变形。如何准确地预测隧道的变形并采取措施最大程度减小隧道的上抬变形是一个难题。本文提出了一种新的简化分析方法,用于预测邻近基坑开挖卸荷引起的既有隧道纵向变形。通过引入弹性层状理论,得到了轴对称荷载作用下分层地基中的附加应力解。考虑隧道剪切变形的影响,将地铁隧道视为搁置于Winkler地基上的Timoshenko梁。基于该解析理论比较了分层地基和均质地基中由于开挖卸荷作用在隧道上的附加应力,并通过两个工程实例验证了解析理论的有效性。在此基础上,对基床系数、基坑开挖中心距隧道纵轴偏移距离和等效剪切刚度的变化引起的隧道变形响应进行了参数分析。研究成果可为类似工程提供理论依据。

The excavation of foundation pit generates soil deformation around existing metro tunnel with shield driving method,which may lead to the deformation of tunnel lining.It is a challenge to evaluate the deformation of shield tunnel accurately and take measures to reduce the tunnel upward displacement as much as possible for geotechnical engineers.A new simplified analytical method is proposed to predict the longitudinal deformation of existing metro tunnel due to excavation unloading of adjacent foundation pit in this paper.Firstly,the additional stress of soils under vertical axisymmetric load in layered soil is obtained by using elastic multi-layer theory.Secondly,the metro tunnel is regarded as a Timoshenko beam supported by Winkler foundation so that the shear effect of tunnels can be taken into account.The additional stress acting on the tunnel due to excavation unloading in layered soil are compared with that in homogeneous soil.Additionally,the effectiveness of the analytical solution is verified via two actual cases.Moreover,parametric analysis is conducted to investigate the responses of the metro tunnel by considering such factors as the variation of subgrade coefficient,offset distance from the excavation center to tunnel longitudinal axis as well as equivalent shear stiffness.The proposed method can be used to provide theoretical basis for similar engineering project.