落石冲击大跨度拱形明洞结构作用机理研究

Research on the Action Mechanism of Rockfall Impacting Large Span Arched Open Cut Tunnel Structure

研究目的:为探明落石冲击作用于拱形明洞结构荷载分布规律,确保明洞结构安全,本文以铁路双线双耳墙式明洞为研究对象,采用有限元软件ANSYS/LS-DYNA,通过改变落石质量、冲击速度和回填土厚度分析落石冲击力和落石冲击所在横、纵断面明洞结构受到的冲击压应力,提出计算落石冲击力、冲击压应力的方法。研究结论:(1)当回填土厚度从1 m增大至4 m时,落石冲击力没有明显变化,而落石冲击作用于明洞结构的最大压应力迅速减小,说明应以落石冲击压应力和回填土自重应力作为明洞结构设计依据;(2)落石冲击压应力随着距落石冲击点水平距离的增大而减小,近似成圆台形分布,其扩散角约为50°;(3)落石冲击力、冲击压应力随落石质量、冲击速度的增大而增大;(4)综合落石质量和冲击速度提出了以冲击能量计算落石冲击力和冲击压应力的方法;(5)本研究成果可为明洞设计提供参考。

Research purposes:In order to find out the load distribution law of acting on arched open cut tunnel structure under rockfall impact,and ensure the safety of open cut tunnel structure,the double-ear wall open cut tunnel of railway double-line was takes as the research object,the finite element software ANSYS/LS-DYNA was used to analyze the impact force of rockfall as well as the impact compressive stress of the cross section and vertical section of rockfall impact point of the open cut tunnel structure,with changes of the rockfall mass,impact velocity,and backfill thickness.A method for calculating the impact force and impact compressive stress of rockfall was proposed.Research conclusions:(1)The impact force of rockfall has not changed significantly while the maximum impact compressive stress of rockfall acting on the open cut tunnel structure decreases rapidly when the thickness of backfill increases from 1 m to 4 m.This indicates that the impact compressive stress of rockfall and gravity stress of backfill should be used as the basis for the design of the open cut tunnel structure.(2)The impact compressive stress of rockfall decreases with the increase of horizontal distance from the impact point of rockfall,and its shape is approximately circular truncated cone.The diffusion angle of impact compressive stress is about 50°.(3)The impact force and impact compressive stress of rockfall increase with the increase of mass and impact velocity of rockfall.(4)The method of calculating the impact force and impact compressive stress of rockfall by impact energy is proposed based on the mass and impact velocity of rockfall.(5)The research results can provide reference for the design of the open cut tunnel.