Research On The Dynamic Response Of Existing Cracks In Tunnel Structure Caused By A Running Subway Train

Due to the uncertainty and complexity of the stratigraphic environment in which the subway tunnel structure is located,diseases such as water leakage,lining structure cracking and corrosion,and structural deformation often occur.Whether the damaged tunnel structure will aggravate the existing damage under the action of train load,which in turn will affect the safety and stability of the tunnel structure,is a topic that needs to be studied in depth.Based on the above problems,this paper mainly studies the dynamic response of the existing crack tip of the tunnel structure under the load of the subway train and the dynamic effect of the train load on the distribution of the existing cracks in different positions and directions.In this paper,taking the distribution of cracks in the lining structure of the horseshoe tunnel of Beijing Subway as the background,this paper establishes a "tunnel-stratigraphic" extended finite element model of the tunnel lining structure that distributes existing cracks in different positions and directions,and analyzes the dynamic response of the tunnel lining crack under the action of train load from two angles: the stress strength factor of the crack tip and the main stress of the crack tip unit.The research results can provide a reference for the maintenance of existing cracks in the tunnel lining structure.The main research content of this article is as follows:(1)Based on the extended finite element method,a numerical model of rectangular plate with surface cracks on one side is established.By applying noninverting resonant loads with different frequency characteristics at both ends of the rectangular plate and comparing them with the analytical solution,on the one hand,the accuracy of dynamically solving the stress strength factor of the crack tip by extended finite element method is analyzed,and on the other hand,the influence of the loading frequency on the stress strength factor of the crack tip is explored.(2)Based on the distribution characteristics of cracks in the horseshoe-shaped tunnel lining of Beijing Subway,a "tunnel-stratigraphic" extended finite element model of existing cracks distributed in different positions and directions of tunnel lining structure is established,and the dynamic response law of existing cracks in tunnel lining structure under train load is explored.The results of the above study show that:(1)The stress strength factor of the crack tip of the dynamic solution is carried out by extended finite element method with high accuracy.With the increase of the loading frequency(1～120Hz),the stress intensity factor shows a certain degree of increase,but the impact of the loading frequency on the stress intensity factor is small.The stress intensity factor value is more positively correlated with the peak of the load and less positively correlated with the loading frequency.(2)From the perspective of train load,the peak of the crack power response of the tunnel lining under the action of the train load appears in the range of 0～10Hz and40～60Hz,and the resonance of the vehicle’s under-spring mass on the quasi-static load of the subway train and the track stiffness plays a major role in the lining crack dynamic response.(3)Under the load of a single subway train,the existing cracks in the tunnel lining vault,arch waist,longitudinal length and circumferential wall will not enter the stable expansion stage,and the cracks will not expand,but the train operation will have different expansion trends on the cracks in different positions and directions of the lining.In addition to the vault position,the influence of train load on the longitudinal crack in the tunnel structure is greater than that of the annular crack;the longitudinal crack tip is mainly subjected to tensile stress and has a type I crack expansion trend;the annular crack tip is mainly subjected to shear stress and has a type II crack expansion trend.The dynamic effect of the train load on the crack in the position of the side wall is greater than the effect on the crack in the position of the vault.