Dynamic response of RC plate with different cushion layers under the high-level rockfall impact

Since the “5.12” Wenchuan Earthquake in 2008, extraordinarily serious collapse hazards have occurred in the shattering mountains. Due to the high position, high impact energy, high difficulty of the active measurement when implementing and the insufficient energy level of the passive protecting net. Thus pile-plate retaining wall structure has been widely used in Wenchuan, Lushan and Jiuzhaigou earthquake-stricken areas to prevent high-level collapse and rockfall, and very good results have been achieved. However, it is also found that there is no cushion or waste tires behind some of the pile-plate retaining wall, so that the high-level rockfall directly impacts the pile-plate retaining wall and causes structural damage. Therefore, in order to avoid the direct impact of the rigid damage caused by the rockfall on the RC plate, the excavated gravel soil is often used as a cushion layer to decrease the impact force. Based on the rockfall block impact test platform, the energy dissipation effect of different types of cushion layer and the dynamic response of RC plate under impact is examined, and a series of rockfall impact tests with different cushion are carried out. The results show that under the same total thickness, the EPS-sand composite cushion has the best energy consumption effect, followed by gravel soil, and sand is the worst. Compared with the other two cushion layers, the impact of rockfall block on the composite cushion has multiple rebounds and the contact time is much longer than the others. Under the same impact condition, the center position of the EPS material collapses and sinks. A large number of radial wide cracks are generated. The composite cushion can effectively reduce the mid-span displacement of the RC plate. Under the falling height of 3 m, 5 m and 7 m, the mid-span displacement is reduced by 37%~46% compared with the sand cushion. Under the impact of R4 block, the displacement of the RC plate is significantly increased, and the plastic displacement is obvious. With the increasing impact energy, the mid-crack extends from the bottom to the top, and the failure mode of the RC plate is bending.