Research On The Influence And The Prediction Of Uneven Settlement On Urban Shield Tunnel

With the continuous increase of Beijing metro line and the continuous increase of operation time,the tunnel disease is becoming more and more serious.Especially,the problems of water leakage,cracks and fault are outstanding in the section of Beijing airport line shield tunnel,in order to control the disease effectively,it is necessary to understand the causes of the disease,mechanism of action and other issues,therefore,firstly,this paper starts from the field investigation of the airport line shield tunnel,and detects and sorts out the quantity,location and characteristics of the leakage water,cracks,dislocation and other diseases.Through the analysis,it is found that the leakage of water is mainly concentrated in the vault of the shield tunnel,and the cracks mainly appear in the arch and the vault.The most serious dislocation is located at the foot of the arch.Based on the analysis of the distribution characteristics of the disease in the airport line,the main reason for the high incidence of the disease in the shield segment is the uneven settlement of the tunnel.In order to study the influence of uneven settlement on shield tunnel,firstly,the causes of uneven settlement of tunnel are analyzed from two aspects of construction period and operation period;Then,using the ABAQUS finite element software,relying on the field test data,the 32 ring three-dimensional shield tunnel model is established,and the stress analysis of the shield tunnel segment caused by uneven settlement is carried out.The results show:(1)When there is no settlement,the inner and the outer side of the vault of the shield tunnel are pulled,and the inner side of the arch is compressed;(2)When the settlement of shield tunnel segment maximum tensile stress occurs in the dislocation segment near the maximum settlement value reached 20mm,and the location of maximum vault tensile stress exceeds the ultimate tensile stress and the tensile failure happened inside the vault;(3)When the settlement value reaches 45mm,the maximum compressive stress in the inner side of the arch is more than the ultimate compressive stress,at the same time,the yield failure occurred in the segment bolts;Finally,the intluence of uneven settlement on the limit state of shield tunnel is calculated by empirical formula,and the results are compared with the numerical simulation results it is found that the calculated results are very close,the results verify the aecuraey of the numerical simulation,the paper puts forward the lmut value of the shield tunnel settlement 50mm,alarm value 40mm,warning value 35mm and the prediction of shield tunnel under different settlement values.The innovation of this paper lies in:(1)In the process of numerical simulation of uneven settlement,the paper not only considering the longitudinal direction of the uneven settlement,but also consider the structure force after the lateral deformation effect;(2)In order to simulate the splicing of six segments,rings and rings,and the connection between segment and bolt,a complex structural model is established;(3)This paper is based on the project of "Theoretical study on shield tunneling of Beijing Metro based on initial damage".The numerical simulation results are combined with the engineering practice to ensure the accuracy of the conclusion.