Study On The Trains Dynamic Response Of Large Diameter Shield Tunnel Affected By Cavitiy Behind The Segement

The cavity behind the tube sheet of shield tunnel is one of the main defective diseases,which is prone to cause structural damage under the action of train vibration load.Therefore,it is necessary to generalize the distribution law of statistical voids and study the influence of train operation on the lining vibration response.In this paper,the dynamic response analysis of tunnel structure under the influence of voids is carried out in conjunction with the Xinzheng Airport-Zhengzhou South Station intercity railroad project.The main research contents are:(1)Based on the summary of literature,the causes of the cavity behind the tube sheet of shield tunnel are analyzed from both construction and operation aspects;combined with the field inspection data of related scholars,mathematical and statistical methods are used to sort and categorize the cavity behind the tube sheet based on the distribution characteristics,and it is concluded that the probability of the cavity behind the tube sheet occurring in the upper half is higher.In terms of the geometry of the cavity,the circumferential angle is generally distributed in the range of 10° ～ 60°,the longitudinal length is distributed in the range of 3 m～ 6 m,and the radial length is distributed in the range of 0.1 m ～ 0.3 m.(2)The finite element software was used to construct a refined simulation and analysis3 D model of the discontinuous contact of railroad bed-tunnel tube sheet-perimeter rock,and reasonable parameters related to the intrinsic model,material parameters,structural damping,boundary conditions,cell type and inter-tube sheet contact were selected.The excitation force function is used to simulate the train vibration load by considering the smoothness of travel,power additional hub and waveform abrasion,etc.The calculated acceleration values are compared and analyzed with the field test acceleration values to verify the accuracy of the numerical simulation.(3)The intrinsic mechanism of the force changes of the cavity behind the tube sheet on the shield tunnel lining under the train load was obtained by considering the cavity along the circumferential direction of 15°,30°,45°,longitudinal length of 2 m,3.3 m,4.6 m,radial height of 0.4 m,positioned in the combination form of single cavity,right arch waist,left arch waist and multiple cavities.The conclusions are as follows:The existence of the cavity makes the dynamic response of the lining change,and the acceleration response of the cavity measurement point and the surrounding measurement points increases significantly,and increases with the increase of the scale of the cavity,and the acceleration response of the arch waist position is larger than that of the arch top.The cavity makes the circumferential stress change from compressive stress to tensile stress from the center of the cavity to both sides of the cavity.When the size of the cavity increases at the vault location,the peak circumferential tensile stress around the lined cavity and the total stress between the contact surfaces on both sides,the tension,slip and bolt tensile stresses increase.At the arch waist,with the increase of the cavity circumferential angle,the peak circumferential tensile stress and the total stress between the contact surfaces on both sides of the cavity,the amount of tension,slip and bolt tensile stress all appear to increase first and then decrease,and the increment on the same side of the train is larger than that on the opposite side of the train and larger than that on the top of the arch.With the increase of longitudinal length of cavity at the arch waist,the peak circumferential tensile stress and the total stress between contact surfaces,tension,slip and bolt tensile stress on both sides of the cavity increase,except that the total stress between contact surfaces is smaller than that on the opposite side of the train,and the other indicators are larger than that on the opposite side of the train and larger than that on the top of the arch.In the combination of multiple cavities,the acceleration,circumferential stress and contact characteristic response changes at the same cavity measurement points are smaller than those of single cavity,and the cavity only has a greater influence on the dynamic response of the lining structure in the center and around it,and has less influence on the other positions of the lining.(4)Sensitivity analysis is carried out for each factor of the cavity behind the tube sheet affecting the dynamic performance of the shield tunnel lining,calculating the influence of the cavity circumferential,longitudinal and location factors,and constructing the mapping relationship of the maximum tensile stress of the tunnel lining tube sheet under the train driving in the cavity behind the tube sheet by single-factor analysis with the maximum tensile stress of the lining around the cavity as the index,and proposing the sensitive factors affecting the tunnel lining structure under the cavity behind the tube sheet.The maximum tensile stress prediction model of the surrounding tube sheet structure when a cavity exists from the vault to the waist of the vault is derived through orthogonal design for mutual coupling of multi-factor cavity influence parameters,which solves the safety evaluation problem of tunnel lining-perimeter rock complex spatial structure system correlation and forms the basis for operation and maintenance decision of shield tunnel affected by train load under cavity behind tube sheet condition.