考虑地基变形连续的基坑开挖诱发邻近盾构隧道位移预测

Prediction of shield tunnel displacement due to adjacent basement excavation considering continuous deformation of ground

从工程实际出发,建立考虑基坑坑底及侧壁卸荷作用的基坑开挖引起的附加荷载计算模型;基于Mindlin解给出由基坑开挖所引起的邻近隧道处的竖向附加荷载;引入能考虑隧道任意埋深效应的修正基床反力系数,将既有隧道简化为搁置于Pasternak地基上的Euler-Bernoulli梁,进而提出基坑开挖下邻近既有隧道响应的简化计算方法.所提方法能考虑隧道埋深效应以及地基剪切效应,与工程实际更为接近.通过与三维有限元以及2组已发表工程实测数据的对比,验证所提简化计算方法的合理性与适用性.针对地基弹性模量、地基剪切模量、隧道纵向等效抗弯刚度、隧道-基坑夹角、隧道埋深、隧道-基坑间距以及基坑几何形状等主要参数对隧道纵向位移的影响进行系统分析.结果表明:隧道与基坑平行工况下的隧道最大位移是垂直工况下的1.60倍;提高隧道纵向抗弯刚度可以有效减小隧道的最大位移,但这种"削弱作用"会随隧道-基坑间距的增大而减小;随着隧道埋深、隧道-基坑间距的增大,隧道最大位移呈非线性递减规律;基坑的"长开挖"会影响隧道的位移和隧道隆起范围,而"短开挖"则主要影响隧道的位移.研究成果可以为较为合理地预测既有盾构隧道在邻近基坑开挖下的响应规律提供理论支持.

A simplified vertical additional load calculation model of basement excavation,considering the unloading effect of bottom as well as sidewalls,was established based on the engineering practice.The vertical additional load at adjacent tunnel caused by basement excavation was given based on the Mindlin solution.A simplified calculation method was proposed for the response of tunnel subjected to an adjacent basement excavation,by introducing a modified subgrade reaction coefficient which could consider the arbitrary tunnel buried depth and regarding the existing tunnel as a continuous Euler-Bernoulli beam resting on Pasternak foundation.The proposed method could consider the effect of tunnel buried depth as well as the ground shear effect,closer to the engineering practice.The rationality and the applicability of the proposed method were verified by comparing it with the three-dimensional finite element method,as well as two groups of published engineering measured data.The main parameters such as elastic modulus and shear modulus of ground,the longitudinal equivalent bending stiffness of tunnel,the angle between tunnel and excavation,the embedded depth of the tunnel,the distance between tunnel and excavation as well as the geometric shape of excavation were all systematically studied.Results indicate that the maximum tunnel vertical displacement,when the tunnel was parallel to the excavation,was 1.60 times of that when the tunnel was perpendicular to the excavation.The maximum displacement of the tunnel can be effectively reduced by increasing the longitudinal bending rigidity of the tunnel,but this“reducing effect”will decrease with the increasing distance between the excavation and the tunnel.The maximum displacement of the tunnel exhibits a non-linear decreasing law with the increase of the tunnel buried depth and the distance between tunnel and excavation.The"long excavation"will affect the displacement and the uplift range of the tunnel,while the"short excavation"mainly affects the tunnel displacement.Results could provide some theoretical support for reasonably predicting the response of existing tunnel due to adjacent excavation.