Analysis On The Influence Of Boundary Effect On The Surface Settlement Induced By Shield Tunneling

The ground displacement induced by shield tunneling will lead to the deformation and destruction of the ground buildings or pipelines,and influence the normal use of the public facilities.Therefore,it is very important to predict the ground displacement introduced by shield tunneling accurately.Among numerous methods of predicting surface displacement,how to choose inner and outer boundary directly affects the accuracy of prediction.In this paper,the influence of the inner and outer boundary on the surface displacement caused by shield tunnelling is studied and analyzed based on the empirical methods and analytical solutions.Finally,on account of the Tsinghua Yuan tunnel,the measured surface settlement is fitted and analyzed.And the main work and achievements are as follows:(1)The classical shield tunnel settlement prediction formula at home and abroad is summarized and analyzed.The empirical formula is classified according to the correlation degree of h,R,? and K,and the analytical formula is classified according to the correlation degree of inner and outer boundary.Then the applicability and characteristics of these classical prediction formulas are put forward.(2)The influence of outer boundary on the surface displacement induced by shield tunneling is studied and analyzed.The effects of the bottom boundary range,the bottom boundary with stiff layer or the horizontal boundary range on the surface displacement are given respectively.Then the distinct effects of homogeneous layer boundary and stiff layer boundary on the surface subsidence are analyzed and compared.Finally,the relationship between the bottom boundary range and the horizontal boundary range are put forward,even the relation formula between them is established.(3)The influence of inner boundary on the surface displacement induced by shield tunneling is studied and analyzed.Basing on the theory of ground loss,the calculation methods of width parameter of surface settlement trough and the ground loss parameter are analyzed and compared respectively,and the applicability of these methods are put forward.Then three basic deforming components of the tunnel boundary include the uniform radial contraction,the ovalization deformation and the vertical displacement are established,so the soil displacement of the tunnel periphery is given and the deformation state of it is studied.Next,The new analytical solution of the surface displacement based on three kinds of tunnel-deforming patterns is established,and the influence of the three tunnel-deforming models on the surface settlement trough is analyzed.Furthermore,a new tunnel-defoming model is put forward,which has been applied to the engineering practice and achieved good results.And the effects of analytical solutions considering the uniform radial displacement lonely or thenon-uniform radial displacement on surface settlement are discussed and evaluated.Finally,the reasonable range of the bottom boundary using Bobet analytical solution and the acquisition methode of ovalization deformation coefficient are put forward.(4)Relying on the engineering practice of the Tsinghua Yuan tunnel,the measured datas of the surface settlement about the two and three shield section are collated and analyzed,then the width parameter of surface settlement trough is obtained by Gauss fitting.The feasibility of using the linear regression method to correct the Peck's empirical formula is put forward.Finally,the reasonable range of relevant parameters of the revised Peck's formula is determined.