Hydraulic Damage Characteristics Of Cracks Adjacent To Sleepers Of Twin-Block Ballastless Track

Twin-block ballastless track is one of the main forms of high-speed railway track structure in China,with simple and reliable,convenient construction and low construction costs and other advantages.However,in the course of lone-term operation,the twin-block ballastless track inevitably suffers from various damages,such as the crack adjacent to the sleeper,the loosening of the sleeper and so on.In rain-rich or improperly drained areas,rainwater can easily soak into the cracks adjacent to the sleeper,accelerating the process of the damage of the twin-block sleeper.The integrity and stability of the track structure will be greatly weakened and the fatigue life of the track structure will be reduced when the twin-block sleeper damaged,therefore,it is necessary to carry out research on the hydraulic damage characteristics of the sleeper of the twin-block ballastless track,which has important theoretical and engineering significance for guiding the maintenance and repair of ballastless track and extending the service life of track structures.In this paper,the crack adjacent to the twin block sleeper was taken as the object of the study,the spatio-temporal distribution characteristics and the propagation behavior under the high-speed train load are investigated by establishing the hydraulic fracturing calculation model of the crack adjacent to the sleeper.The main findings and results are as follows:(1)Based on document collection and field investigation,the types of hydraulic damage of twin-block ballastless track are summarized,and development process of the hydraulic damage of twin-block sleeper are defined.(2)The calculation model of hydrodynamic pressure in the crack adjacent to the sleeper is established,and the analytical expressions of the hydrodynamic pressure in triangular,trapezoidal and parabolic cracks under external load are derived based on the integral expressions of the law of conservation of mass and theorem of momentum.(3)The correctness of the analytical expression of hydrodynamic pressure in the crack was verified based on the establishment of the fulid–solid coupling finite model of the twinblock ballastless track,and then the hydrodynamic pressure distribution characteristic in the crack under the harmonic load was calculated.The results show that: the hydrodynamic pressure in the crack in influenced by many factors such as the amplitude and frequency of the external load,the geometrical shape of the crack and so on;The sharper the crack tip,the higher the hydrodynamic pressure,so the hydrodynamic pressure of the triangle and the parabolic crack is much greater than that of rectangular crack.(4)The hydrodynamic pressure in the crack adjacent to the twin-block sleeper under the high-speed train load is solved based on vehicle-track coupling dynamic theory,the influencing factors and spatial and temporal distribution characteristics of the hydrodynamic pressure in the crack were investigated.The results show that: The crack opening is the main factor affecting the hydrodynamic pressure in the crack,the train speed and the crack length also have some influence on the hydrodynamic pressure;The hydrodynamic pressure reaches its maximal and minimal value when the wheelset and the center of the bogie are close to the damaged area;The spatial distribution of hydrodynamic pressure in the crack is complex and its value decreases sharply along the direction of the crack exit.(5)Based on fracture mechanics theory,the hydraulic fracture finite element calculation model of the crack adjacent to the twin-block sleeper was established to investigate the hydraulic fracture characteristics of cracks under the high-speed train load and hydrodynamic pressure.The results show that: the crack adjacent to the sleepers belong to the mixed-mode crack of the opening mode and sliding mode,but the sliding type is the main form of damage;The equivalent intensity factor at the crack tip increases with the increase of the train speed and the crack length,and increase with the decrease of the crack opening;The unstable fracture length of the crack adjacent to the twin-block sleeper decreases with the increase of the train speed and the decrease of the crack opening.