Numerical study of rockfall impact on bridge piers and its effect on the safe operation of high-speed trains

Bridges situated in mountainous regions are vulnerable to rockfall collisions, which may endanger the safe operation of high-speed trains that travel on these bridges. This article presents numerical simulations of collisions between falling rocks and piers to investigate impact forces, bridge responses and track structural deformation by using the finite element code LS-DYNA. A two-step numerical modelling technique is proposed to determine the operational safety indices for high-speed trains. The influences of rockfall velocity, diameter, impact location and train speed on the impact forces, pier-top displacements and train operational safety indices are investigated based on a case study. Results show that the rockfall impact force can be characterized by a very short impulse that has an obvious effect on bridge dynamic responses. The additional track irregularity caused by the bridge girder displacements can notably amplify the train operational safety indices, especially for the indices of derailment factor and lateral wheel/rail force. The high-speed train is in an unsafe operational state for a falling rock diameter of 1 m when the rock falling velocity reaches 30 m/s or for a falling rock velocity of 20 m/s when the diameter is greater than 1.5 m.