落石冲击破碎特征的加载率相关性研究

Loading Rate Dependency of Impact Induced Rock Fragmentation During Rockfall

落石在与地面碰撞的过程中易发生破碎,形成较多能量大、形状各异的岩石块体,从而增加了落石的危害性。长期以来,由于对落石破碎后的运动轨迹、能量演化、块体尺寸分布等的量化存在较大困难,并且落石的破碎解体还没有被考虑到落石的运动学分析中。因此,研究落石的冲击破碎机理,判断落石是否破碎及预测破碎块体的大小将促进落石运动分析的进一步发展。本文运用离散单元方法建立落石与地面的数值模型,落石由紧密黏结的球形颗粒组成,刚性地面由一层固定颗粒代替,研究落石在不同速度撞击下的破碎特征,分析落石破碎特征与冲击加载率的关系。结果表明:落石在撞击地面后,内部瞬间产生大量的裂纹,这些裂纹相互贯通,便将落石破裂成不同大小的块体;随着冲击加载率的增大,落石内部产生的裂纹急剧增加,致使落石破碎的块体数目增多,块体尺寸减小;落石的破碎程度与加载率呈线性正相关关系,破碎块体数量和最大块体尺寸与加载率呈幂函数关系,且破碎块体的尺寸分布特征符合三参数极值分布。

The rock block can be fragmented readily during rock-fall or rock-avalanche.This process produces many highly energetic and randomly sized rock fragments which can be very hazardous to human lives and lifeline facilities nearby.However,the upon impact of rock fragmentation is usually not considered in the analysis of rockfall kinematics,because the trajectories and destructive power of rock fragments are very difficult to predict.Therefore,the investigation of the rock fragmentation mechanism plays a critical role in the analysis of rockfall kinematics.In this paper,the discrete element method was applied to establish a numerical model of rock block impacting on a rigid ground.The spherical rock block was represented as an assembly of densely packed particles.The rigid ground was represented by a layer of fixed particles.The relationship between the impact loading rate and the fragmentation characteristic were analyzed.The results indicated that the instantaneous impact can lead to a lot of fractures generated in the rock block.The nucleation of these fractures breaks the rock block into fragments.As the impact loading rate increases,the fragmentation intensity and number of fragments increase,while the fragment size decreases.The number of fragments and the maximum fragment size both exhibit a power law dependence on the impact loading rate.The fragments size distribution could be well fitted by the three parameters generalized extreme value distribution function.