In the top of the rock shed,a certain thickness of sand cushion could play a significant energy dissipation function.The effect of different thickness of sand cushion is greatly diverse.Hence,how to determine the thickness of sand cushion became one of the key issues in the shed design.Based on the actual shed tunnel structures as prototypes,the dynamic finite element numerical simulation was used to analyze the dynamic response of sand cushions with multi thickness under different impact energies and the mechanism of energy absorption.The results showed that under low impact energy,the changes of sand cushion thickness had little influence on the rock fall impact force,whereas there were extremely differences in the energy absorption of different thickness sand cushions under high impact energy.Increasing the thickness of sand cushions could effectively weaken the slabs’deformation caused by rock fall impact,however enlarged the weight of structures.With the consideration of both economic rationality and structural reliability,the optimal cushion thickness was obtained by calculation.
