落石连续冲击下废弃混凝土垫层宏细观缓冲机制研究

Macro-mesoscopic investigation of cushioning mechanism of recycled concrete aggregate under successive rockfall impacts

棚洞等刚性防护结构中具有良好缓冲性能的垫层材料可以有效削减冲击荷载,提高结构抗冲击能力。为研究重复冲击下再生混凝土垫层宏观缓冲性能演化规律,开展了落锤冲击试验和离散元数值模拟研究。试验结果表明,相比于石英砂垫层,首次冲击下采用再生混凝土骨料垫层防护的棚洞顶板中心处传递力减小了83%,且应力分布更加均匀。随着落锤重复冲击次数增加,再生混凝土骨料和石英砂垫层缓冲性能均存在劣化现象,第6次冲击时棚洞顶板中心传递力峰值分别为首次冲击的11.2倍和1.4倍。此外,数值模拟研究结果发现,当长条状颗粒数量占比由0%增大到100%时,颗粒旋转角度和平移距离分别减小了40%和20%,落锤冲击力峰值增加了37%。颗粒形状越不规则,颗粒间咬合程度越大,限制了颗粒旋转和平移,增大了滚石冲击力和挡墙传递荷载。该研究成果可为再生混凝土骨料作为新型绿色垫层提供理论依据和工程指导。

Cushion materials can effectively reduce the impact load acting on the rigid protective structures such as shed tunnel and improve the impact resistance of the structures.In order to investigate the variation of cushioning performance of recycled concrete aggregate(RCA)under successive impacts,drop weight impact tests and discrete element simulations are carried out.Test results show that compared with the quartz sand cushion layer,the transmitted load at the center of concrete shed for RCA under the first impact reduces by 83%,and the transmitted load is distributed more uniformly.With the increase of impact times,both the cushioning performances of RCA and quartz sand deteriorate.For the sixth impact,the maximum transmitted loads at the center of concrete shed for RCA and quartz sand are 11.2 times and 1.4 times larger than those of the first impact,respectively.Furthermore,the cushioning performance is strongly influenced by particle shape.The numerical simulation results show that if the proportion of long particles increases from 0%to 100%,the rotation angle and translation distance of the particles decrease by 40%and 20%,respectively,and the maximum drop weight impact load increases by 37%.The inter-locking effect between particles increases with the irregularity of particle shape,which limits the rotation and translation of the particles,and increases the drop weight impact load and the transmitted load on the concrete slab.The research results may provide theoretical basis and engineering guidance for recycled concrete aggregate as a new type of eco-friendly cushion.