The buffering performance of a flexible buffer-sand layer composite cushion used for rockfall shed: experimental and numerical investigation.

A common practice in mountainous areas for rockfall protection is to cover the top slab of a rockfall shed with a thick granular layer to buffer the impact. However, the weight of the sand is significant, with limited buffering capacity. This paper proposes a novel composite cushion consisting of a flexible buffer and a sand layer. Full-scale rockfall impact tests of 500 kJ were conducted to evaluate the performance of the cushion. Based on the sand layer impact test, DEM parameters for simulating sand were calibrated, and a numerical model of the composite cushion with rockfall impact using FEM-DEM coupling method was constructed. The buffering performance of the composite cushion was compared with the EPS-sand cushion. The study further investigates the effect of buffer height, sand layer thickness, and rockfall mass on impact force and energy distribution using numerical simulations. The results show that (1) the impact force on the composite cushion decreases by 73.2% compared to the sand layer. (2) The buffering performance of the composite cushion is equivalent to that of the 1 m EPS + 0.4 m sand cushion in terms of inhibiting the stress development on the shed slab. (3) The superior buffering performance of the cushion is attributed to the high flexibility of the net and the force-controlling characteristics of the energy dissipaters. Meanwhile, the sand layer plays more of a secondary defense role to prevent direct collision between the rockfall and the shed slab. These findings provide theoretical bases for the engineering design of such composite cushions. [ABSTRACT FROM AUTHOR]