冲击荷载下颗粒级配对废弃混凝土骨料垫层缓冲机理影响研究

Effects of particle-size distribution on buffering mechanism of waste concrete aggregate cushion layer under impact load

在棚洞等防护结构上方铺设散体材料垫层能够大幅削减落石冲击力和棚洞顶板传递力,提高防护结构抗冲击性能。为了研究颗粒级配对新型废弃混凝土骨料垫层缓冲性能的影响规律,分别开展室内落锤冲击试验和三维离散元数值模拟。结果表明:对于单一粒组颗粒垫层,当均一化颗粒粒径(d_(50)/R)由0.15增加至0.75时,由于力链中潜在失稳点减少,力链稳定性增强,颗粒重排机制受限(平均位移和转角分别减少了41.3%和33.7%),落锤冲击力和棚洞顶板传递力峰值分别增加了36.3%和282.2%;对于复合粒组颗粒垫层,当不均匀系数(C_(u))由1.1增加至8.0时,粗颗粒周围孔隙被细颗粒填充,配位数增加,导致力链稳定性增强,颗粒重排机制受限(平均位移和转角分别减少了22.4%和45.3%),落锤冲击力和棚洞顶板传递力峰值分别增加了26.0%和174.6%;基于试验和数值模拟结果提出与均一化颗粒粒径(d_(50)/R)和不均匀系数(C_(u))相关的垫层防护折减系数α,建立考虑垫层防护作用的落锤冲击力半经验公式,为山区棚洞工程设计与施工提供技术支撑和理论指导。

Laying a loose material cushion layer above protective structures of shed tunnels,etc.can significantly reduce impact force of falling rocks and transmission force of shed roof to improve anti-impact performance of protective structures.Here,to study effects of particle-size distribution on buffering performance of new type waste concrete aggregate cushion layer,indoor drop hammer impact tests and 3-D discrete element numerical simulation were conducted,respectively.The results showed that for cushion layer with same particle size,when the homogenized particle size d_(50)/R increases from 0.15 to 0.75,due to potential instability points in force chain decreasing,the stability of force chain increases,and the particle rearrangement mechanism is limited,average displacement and rotating angle deceases by 41.3%and 33.7%,respectively to cause peak impact force of drop hammer and peak transmission force of shed roof increasing by 36.3%and 282.2%,respectively;for cushion layer with different particle sizes,when the non-uniformity coefficient C_(u) increases from 1.1 to 8.0,pores around coarse particles are filled with fine particles,the coordination number increases,the stability of force chain increases,the particle rearrangement mechanism is limited,average displacement and rotating angle decreases by 22.4%and 45.3%,respectively and peak values of drop hammer impact force and transmission force of shed roof increase by 26.0%and 174.6%,respectively;based on test and numerical simulation results,the cushion layer protection reduction coefficientαis proposed,which is related to the uniform particle size d_(50)/R and the non-uniformity coefficient C_(u);a semi-empirical formula for drop hammer impact force considering cushion layer protective action is established to provide technical support and theoretical guidance for design and construction of shed tunnel engineering in mountain areas.