Influence of sand cushion on rockfall-impact resistance of RC sheds

Reinforced concrete (RC) sheds with sand cushions laying on the top are commonly adopted to resist rockfall impacts. To improve the rockfall-impact resistance of RC shed with sand cushion, this study investigated the buffering performance of sand cushion and examined the effect of sand cushion on the dynamic behaviors of RC shed. Firstly, a series of impact tests on sand cushion were conducted to analyze the influence of cushion thickness and falling height of rockfall on the penetration depth into the cushion, impact force and impact duration, as well as the development of vertical and horizontal stresses inside the cushion. Then, a finite element-discrete element coupling model was established to consider the particle interaction of sand cushion under rockfall impacts and impact behaviors of RC shed. Finally, based on the validated numerical analysis method, the effect of sand cushion on the dynamic responses and damage of prototype RC shed subjected to the impact of rockfall was simulated and evaluated. The results showed that: (i) with the increase of cushion thickness, the peak impact force was reduced, but the penetration depth and duration increased; as the falling height elevated, the impact force and penetration depth increased while the duration was shortened; (ii) sand cushion had excellent buffering performance to attenuate vertical and horizontal stresses inside the cushion; (iii) stress diffusion angle formed in the sand cushion can enlarge the load-bearing area at the bottom of the cushion, and the buffering performance of sand cushion can be improved through increasing the stress diffusion angle; (iv) compared with the non-cushion one, the rockfall-impact resistance of RC shed was effectively improved by the sand cushion through reducing impact force, penetration depth, dynamic bending moment and shear force of the shed roof, as well as transforming brittle punching-shear failure of the shed roof into flexural failure.