Research On Interfacial Crack Expansion Of Twin-Block Track Under The Trainload And Water Coupling

Based on the field investigation of twin-block ballastless track,a lot of cracks were found on the surface of twin-block slab which was on the subgrade. After rain flows into the crack, water would be squeezed out from the crack because of the train load,all of which will influence the twin-block track’s security and stability.Therefore,the research of propagation mechanism of crack on twin-block track is extremely urgent.(1)Firstly,through the field research and collecting research materials of the influence of water on ballastless track and concrete crack, the form and causes of cracks and the influence of water on wet concrete strength were sum up.(2)Secondly, for twin-block ballastless track on the subgrade as research, mechanical model of twin-block ballastless track was built.The analysis results indicated:①When the rain flows into the crack which is on the edge of sleeper,the pressure and velocity of monitoring point along the horizontal of slab are equal. While along the thickness direction of slab,the pressure linearly increases and the flow velocity unchanged.(2)The characteristics of the water pressure and velocity as follows:With the increase of crack depth,the pressure and velocity of water at the crack tip gradually increase, when the crack depth reaches the bottom of the sleeper, the maximum pressure of water at the crack tip is15.93kPa and the maximum velocity is0.263m/s;With the increase of crack width and length,the water pressure and velocity is relatively steady.(3)When the crack length is0.8m,width is0.5mm,depth is5cm.With the increase of train load,the water pressure and velocity of crack gradually increase. When the speed of train is160km/h, the maximum water pressure is2710Pa and the maximum velocity is0.14m/s.When the speed of train is350km/h, the maximum water pressure is4140Pa and the maximum velocity is0.223m/s.(3) Based on the fracture mechanics theory and the dynamic characteristics of water, model of twin-block ballastless track was built.The analysis result showed:①With the increase of crack depth,the stress intensity factor of crack tip gradually raises. When the crack depth reaches the bottom of the sleeper, the stress intensity factor of crack tip is23.4N·mm-1.5.Even though it did not reach the fracture toughness of concrete which is54.7N·mm-15, it will be easier to cracke on the influence of temperature.②With the increase of crack width and length,the stress intensity factor of crack tip increases, but the increment is small.