Investigation on cushioning effect and force chain characteristics of cushion material of shed-hole structure under impact load

To reduce the impact of mountain rockfall on the shed tunnel, cushion buffering materials were designed as protective measures. The optimized design can improve the impact energy of rockfall by effectively dissipating it. In the present study, numerical simulation of the impact dynamics of three granular materials (spherical, cylindrical, and square) was investigated by the discrete element method. Particularly, this article discussed how particle shape and V0 (initial impact velocity) affect impact pressure, kinetic energy, friction mobilization, force chain evolution, distribution, transmission efficiency, and anisotropy of granular materials. The results showed that among these three different shapes of granular materials, the spherical granular material had the best cushioning capacity. The sensitivity of impact pressure to particle shape depends on V0, whether or not above Vc (critical initial impact velocity). Besides, as V0 increases, the probability distribution function of the weak contact force is smaller, while the strong contact force is larger, and the decreases exponentially with the increase of force. Furthermore, the transmission capacity of the primary force chain is the best, while secondary force chain transmission is the largest force,Under low velocity impact, the sharper the particle surface, the stronger the spatial negative correlation of the force chain, which increases the spatial normal force and normal relationship of the force chain structure, and thus the stronger the force.