Mechanical Characteristics Of Tunnel Cracks Under Dynamic Load Induced By High-speed Railway Train

With the continuous development of China’s economic construction,high-speed railway network continues to expand and improve,more and more high-speed railway tunnels have been designed and constructed.Compared with the general railway tunnel,the dynamic response of the high-speed railway tunnel is more significant,especially the aggravation of the lining cracking,block falling,water leakage and backside cavity in the tunnel operation period.The negative effect caused by dynamic load of high-speed train becomes more and more obvious with the increasing of train speed.Therefore,it is particularly important to study the defect state of high-speed railway tunnel structure under dynamic train load.It is of great scientific significance and engineering value to explore the development law of tunnel defects under dynamic load for the safe operation of high-speed railway tunnels in China in the future.Article adopts the rigid-flexible coupling model for high-speed train vibration load,based on the three-dimensional fluid calculation software for high-speed train aerodynamic load,through the field measurement data validation under the premise of train vibration/pneumatic loading accuracy,the dynamic(vibration/pneumatic)will load to the tunnel model,so as to explore the mechanical response of lining structure under dynamic loads.First of all,the paper analyzes the structural stress,crack tip stress and crack tip opening displacement under vibration load under different conditions of surrounding rock stress,crack depth and length when there are existing cracks in the slab or invert filling of high-speed train passing by 300 km/h,and obtains the existing crack propagation signs and laws.Then,the structure and crack states of secondary lining arch waist with existing cracks are analyzed under different working conditions under vibration load,and the most unfavorable working conditions are obtained.Finally,the structural mechanical response under the combined action of vibration load and aerodynamic load is further studied.The main conclusions of this paper are as follows:(1)The vibration load obtained by rigid-flexible coupling method is applied to the model with good effectiveness,and the error between simulation and measurement is less than 10%.When the train passes through the tunnel,the dynamic stress of the tunnel substructure decreases with the increase of the depth,and the downward trend gradually decreases.The higher the speed,the greater the dynamic stress.(2)When the stress of surrounding rock is increased,the crack of slab may expand under the train vibration load.The crack propagation law at the slab is that the crack expands both in the depth direction and the tunnel longitudinal direction at the same time,but it expands faster in the depth direction until it stops spreading downward after crossing the track plate and continues to expand in the tunnel longitudinal direction.(3)The sudden change of the crack tip stress and opening displacement is the symptom of the crack propagation.When there are existing crack in the inverted filling,the existing crack propagation law is roughly the same as the crack propagation law at the slab,but the crack initiation condition is different,and the fracture propagation at the inverted filling is more likely to occur.(4)Under the high-speed train load,although there is crack in the secondary lining,the vibration load is not enough to make the crack spread.According to the analysis of vibration and aerodynamic interaction in the most unfavorable conditions,the crack tip stress variation only ranges from 0 to 0.5 kpa after applying aerodynamic load,and the crack tip opening displacement variation range is small.The aerodynamic effect is smaller than the vibration effect when there are cracks in the secondary lining arch.