| With the growth of national economy,our country city changes a process to be accelerated ceaselessly.The projects of excavation and tunnel becomes more and more common.The deformation of the existing tunnel owing to excavation should be paid more attention to.When excavation is close to the existing tunnel,it would lead to the deformation of tunnel as a result of unloading.Deformation which exceed the safety control values would have important effect on the normal usage of tunnel.So it is very important to control the deformation of tunnel.The mothods calculating the deformation of tunel recentely include formule method,test method and numerical simulation method.Recent years,numerical simulation method has been widely used with the development of finite element software,because it is comprehensive,inexpensive and repeatable.However,it is important to choose the right model as well as parameters to get the accurate results.In practice,the deformation of tunnel caused by excavation could be accurately analyzed by finite element analogy when considering the nonlinear and small strain character of soil.The excavation of foundation pit mainly lead to the horizontal deformation of tunnel if it was on either side of the foundation pit.Based on a construction project of deep foundation pit in Tianjin,this paper verified the accuracy of finite element method which considering the nonlinear and small strain character of soil.But it would be difficult to model and choose parameters.In order to solve this problem,parametric study was performed with 2D model to obtain the relationship between the maximum horizontal displacement of tunnel and the excavation depth,the relative location of tunnel as well as the maximum horizontal deformation of retaining structures.Finally,a simplified calculation formula was calculated to predict the maximum horizontal displacement of tunnel in Tianjin soil conditions.It would be more time-saving and convenient to make prediction.The calculated results were compared with the engineering projects.It showed the simplified calculation formula could accurately predict the maximum horizontal displacement of tunnel caused by excavation in Tianjin and other coastal soft soil areas.The excavation of foundation pit mainly lead to the vertical deformation of tunnel if it was under the foundation pit.Based on a project in Zhengzhou,this paper analyzed how the tunnel is lifted owing to excavation considering the nonlinear and small strain character of soil.For the uplifted tunnel caused by the deformation of retaining structure,parametric study was performed with 2D model to obtain the relationship between the maximum vertical displacement of tunnel and the relative location of tunnel as well as the maximum horizontal deformation of retaining structures.According to the deformation controlling criteria of the existing tunnel,the bottom area of excavation was zoned.The influenced zone could be used to predict the deformation of the existing tunnel caused by the deformation of retaining structure,which could be simply characterized by a right trapezoid,according to the relative location of tunnel and the maximum horizontal displacements of retaining structures. |
