高位落石作用下不同缓冲层与钢筋混凝土板组合结构动力响应

2008年“5.12”汶川特大地震诱发了大量的震裂山体危岩崩塌灾害。这类危岩发育位置高、冲击能量大，存在主动加固措施难以实施且被动防护网防护能级不足的问题，为此在汶川、芦山、九寨沟地震灾区逐渐广泛使用桩板拦石墙结构用于防治高位崩塌落石，取得了非常好的效果，但同时也存在部分桩板拦石墙墙后因未设缓冲层或挂废旧轮胎而被落石直接撞击并损毁的现象。为避免落石直接与此类钢筋混凝土（RC）板碰撞造成刚性破坏，工程上常采用就地开挖的碎石土、砂土作为缓冲层以减缓落石冲击力，为研究冲击作用下不同类型缓冲层消能效果及RC板的动力响应特征，基于室外搭建的落石冲击试验平台，开展了不同缓冲层及其相互组合的系列落石冲击试验。结果表明，总厚度相同前提下，EPS泡沫-砂土组合缓冲层的消能效果最优，其次为碎石土，砂最差。与其他两种缓冲层消能方式相比，落石锤与组合缓冲层碰撞过程中发生多次反弹且接触时长远大于其他两种；相同的冲击工况下，EPS中心位置压溃并下陷，且产生大量辐射状宽大裂缝；组合缓冲层能够有效减小RC板的跨中位移，在3，5，7 m冲击高度下，比砂作为缓冲层时跨中位移减小了37%~46%。在R4落石锤冲击下，RC板跨中位移显著增加且产生明显塑性位移，随冲击能量增大跨中裂缝自下而上延伸，RC板最终破坏时表现为典型的弯曲破坏特征。

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.