Soil Settlement And Pile Response Caused By Shield Tunnel Construction And Operation In Soft Clay

The long term settlement of soft clay is very likely to cause deformation or even destruction of tunnel structure and adjacent buildings,so it is necessary to deeply study the settlement of surrounding soil and the response of pile foundation caused by tunnel excavation.On the basis of considering the rheological characteristics of soil,this paper calculates the long term settlement of soil caused by shield tunnel excavation from a theoretical point of view,and carries out numerical simulation about the response of adjacent pile foundation caused by tunnel excavation.The main research contents and conclusions are as follows:(1)Based on the fractional-order viscoelastic constitutive model,it is assumed that the initial excess pore water pressure above the tunnel axis caused by tunnelling is a cubic curve distribution,and the tunnel lining is a semi-permeable water boundary,the long-term settlement formula above the tunnel axis caused by shield tunnel construction is derived by the Terzaghi's one-dimensional consolidation theory and Laplace transformation.Then this formula is used to predict the post-construction settlement of Shanghai Metro Line 1 and analyze the influence of permeability coefficient on post-construction settlement,and the calculated results are consistent with the measured data.(2)The DCM method and fine simulation method are used to calculate the adjacent pile foundation response caused by shield tunnel excavation under elastic model,and compared with the results calculated by GEPAN program,then the advantages and disadvantages of the two methods in numerical simulation are analyzed.And then the fine simulation method is selected to simulate the response of the pile caused by tunnel excavation under the Cvisc model,and the influence of the excavation process on the adjacent pile group during the construction period of shield tunnel is analyzed.(3)The three-dimensional numerical simulation of shield tunnel excavation is carried out by using finite difference software FLAC^3D.By considering the rheology of soil,the time effect of shield tunnel operation period on adjacent piles caused by the rheological action and the variation of blocking effect with time and the effect of pile diameter and pile length on pile response are studied.