Abstract: In order to obtain the fracture evolution mechanism and variation law of bearing capacity of cracked lining under heavyhaul train load, a numerical simulation technique based on the combination of extended finite element method and direct circulation method is adopted to quantitively analyze the propagation path of cracks. Through comparing the numerical simulation with the model test site results, it shows that the error is found to be only 3.7%, thus the propagation path of cracks under train load can be simulated accurately. Research results show that: (1) The dynamic response at the cracked lining invert is more intense than that at other parts of the lining and the safety factor at the cracked lining invert is smaller than at other parts of the lining under heavyhaul train load；therefore, the position of cracked lining invert is the dangerous position under dynamic load of heavyhaul train. (2) The influence of axle load on the dynamic response of cracked tunnel lining is more obvious than that of initial crack depth and speed, and the safety performance of cracked lining is more significantly affected by initial crack depth than by axle load and speed. 

Key words: heavyhaul train, railway tunnel, cracked tunnel lining, dynamic response, bearing capacity