| With the development of the city and the gathering of the population,the urban ground space resources are increasingly scarce,which promotes the demand for underground space development.Since last century,more and more scholars began to pay attention to and study the safety and performance of urban rail transit tunnel.As the main load-bearing structure of shield tunnel in urban metro,various defects are inevitably produced in the construction process of pouring,transportation and assembly.During the normal operation of the subway,the tunnel lining is mainly subjected to soil and water pressure,ground overload and periodic train load,etc.Under the long-term repeated action of these loads,the cracks in the lining concrete will continue to expand and finally lead to the subway tunnel damage.And the normal service can not continue.Nanjing Metro Line 5 is token as a research prototype,a high-precision shield tunnel model is established and the factors affecting the dynamic response of the tunnel are studied.At the same time,the tunnel damage and life estimation are calculated by rainflow counting method,Miner damage accumulation principle and concrete fatigue equation.And it analyzes the path of crack development and influencing factors when there is obvious initial crack in the tunnel.The research content and conclusions of this paper are as follows:(1)A high-precision shield tunnel model is established based on Abaqus,which restores the actual scene where the tunnel segments are spliced by high-strength bolts.Infinite element processing is performed on the boundary to reduce the reflection effect of the wave at the boundary caused by the train load.The three stages of ground stress balance,tunnel excavation and normal operation of the tunnel are simulated.The state of the components of each part of the tunnel under the condition of a subway train with an axle load of 16 t running at a speed of80km/h is analyzed.The calculation results show that the stress state of the tunnel lining and bolts are both in Within the safe range.(2)Based on the theory of track irregularity,the influence of train speed and train axle load on the dynamic response of the tunnel is comparatively analyzed.The simulation results show that the dynamic response of the tunnel is mainly concentrated at the bottom of the tunnel.Within a certain range,the tunnel dynamic stress and vibration acceleration are positively correlated with the train speed and axle load.(3)Assuming that the tunnel has no initial defects,based on the rain flow counting method,the Miner damage accumulation principle and the concrete fatigue equation,the damage at the stress concentration of the tunnel is analyzed,and the life of the tunnel is estimated.The calculation results show that under the premise that bolts and other accessories can ensure longterm effectiveness,the tunnel structure can meet the 100-year life requirement of the subway design.(4)Assuming that the tunnel has initial defects,with the help of extended finite element method(XFEM),initial cracks are set at different positions of the lining segment.The Paris fatigue criterion is introduced to study the propagation law of initial cracks at different locations,and the influence of train speed and train axle load on crack propagation is analyzed.Comparing the numerical results with the prototype test results,it is found that the crack growth law is consistent.The cracks mainly present the characteristics of I-type fracture,and in the process of expansion,there is a tendency to expand toward the stress concentration area.Within a certain range,the crack propagation speed is positively correlated with train running speed and train axle load,but the propagation path and law are similar. |
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