矩形明洞在抵抗落石冲击时,其结构所承受的冲击动力荷载传递过程较为复杂.考虑回填土的离散特性,基于离散单元法建立数值模型,对落石冲击过程进行模拟分析,研究不同落石高度下回填土压实度、回填土厚度以及落石冲击角度对明洞结构冲击响应特征的影响.研究结果表明:(1)回填黄土厚度对落石冲击力影响不大,高压实土条件下落石产生的冲击力更大;(2)竖向冲击能相同时,落石冲击角度对结构承受的冲击荷载影响不大,总冲击能相同时,垂直冲击为最不利工况;(3)填土厚度较小时,其缓冲性能难以充分发挥,明洞顶板承受的冲击荷载远大于厚填土条件下的情况;(4)当竖向冲击能≤1.63 MJ时,回填黄土厚度超过1.5 m后,明洞顶板承受的冲击荷载没有明显改善,此时明洞顶板填土增加的恒载大于减小的冲击荷载;最优回填黄土厚度与落石冲击能相关,当竖向冲击能≤1.63 MJ时,建议回填土厚度不低于1.0 m.
Numerical Study on the Response of Rectangular Open Cut Tunnels with Loess Backfills to the Rockfall Impact
The impact dynamic load transmission process in rectangular open tunnels subjected to falling rocks is highly complex.Considering the discrete characteristics of backfilled soils,a numerical model was established using the discrete element method(DEM)to simulate the impact process of falling rocks.The study investigates the effects of backfilled soil compactions,backfill thicknesses,and rock impact angle on the impact response characteristics of the open tunnel structure under different rockfall heights.The results indicate that:(1)The thickness of loess back-fills has minimal effect on the impact force,while higher compaction results in greater impact forces;(2)When the ver-tical impact energy is the same,the impact angle of falling rocks has little influence on the impact load experienced by the structure,with vertical impacts representing the most unfavorable condition under the same total impact energy;(3)When the backfill thickness is small,its cushioning performance is insufficient,and the impact load on the tun-nel roof is significantly higher compared to conditions with thicker backfills;(4)When the vertical impact energy is≤1.63 MJ,increasing the backfill thickness beyond 1.5 m does not significantly reduce the impact load on the tunnel roof,as the additional static load of the backfills outweighs the reduction in impact load.The optimal backfill thickness is related to the falling rock impact energy;for vertical impact energy≤1.63 MJ,a backfill thickness of no less than 1.0 m is recommended.
Rectangular open cut tunnelDiscrete element methodLoess backfill thicknessRockfall impactEnergy dissipation
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维普
