落石冲击力评定的离散元颗粒流数值模拟

为使落石冲击力评定更合理、有效,以离散元模型(DEM)为理论基础,利用颗粒流(PFC)单元法研究垂直下落条件下落石对结构的冲击力,分析了落石高度、重力及回填土厚度对冲击力的影响规律.将PFC数值模拟结果与其他几种落石冲击力计算方法所得结果进行比较,结果表明:落石冲击力与落石高度及重力均呈明显的线性关系,落石冲击力随落石高度线性变化幅度与落石重力有关,而落石冲击力随落石重力线性变化幅度与回填土厚度有关;回填土厚度为0.6 m时的冲击力比无回填土时减小50%~60%,回填土厚度大于2.0 m时,缓冲幅度趋于稳定,说明回填土厚度有一个合理范围,超出时,结构总荷载会增大;离散元颗粒流数值模拟方法通过阻尼设置来模拟空气在落石下落过程中产生的作用,使得在评定大体积落石从较高高度下落时产生的冲击力更加合理. 

Assessment of Rockfall Impact Force by Particle Flow Code Numerical Simulation Based on Discrete Element Model

To make a reasonable and effective assessment of rockfall impact force, a study on the impact force of falling down rockfall to a structure was carried out by using the method of PFC(particle flow code) based on the theory of DEM(discrete element model). The effects of rockfall height and gravity,and backfill soil thickness on the impact force were analyzed. The results of PFC numerical simulation were compared with those reached by other kinds of calculation methods. The results show that there is an obvious linear relationship between the impact force and the rockfall height or gravity. The linear variation range of the impact force with the changing of the rockfall height relates to the rockfall gravity, while the linear variation range of the impact force with the changing of the rockfall gravity relates to the backfill soil thickness. The impact force reduces by 50%-60% when the backfill soil thickness is 0.6 meter compared with no backfill soil. it tends to be stable when the backfill soil thickness is more than 2 meters, showing that there is a reasonable range of the backfill soil thickness. The total load of structure will increase if the backfill soil thickness exceeds the range. The method of PFC numerical simulation can simulate the effect of air acting on rockfall by setting damping coefficient, which makes the assessment of bigger size rockfall impact force more reasonable.