粒子重复冲击破岩细观损伤及破碎特征试验研究

粒子冲击破岩作为一种新型辅助破岩技术已在钻探和油气开采等领域得到有效运用，其在极坚硬岩层中隧（巷）道辅助掘进方面具有广阔的应用前景。从试验角度研究了粒子的冲击次数、颗粒强度及冲击速度等因素对极坚硬花岗岩表面冲击坑损伤破碎特征的影响，对冲击坑三维形貌、岩石碎屑及坑内矿物破碎特征进行了定量分析。结果表明：成坑最大深度随冲击次数增加呈抛物线趋势增大，而成坑体积和坑顶面积随冲击次数增加呈线性增长；成坑体积随冲击速度呈先增大后减小的规律，该临界冲击速度约为82.5 m/s；冲击坑中心与外部的细观破碎机制差异导致岩石碎屑平均尺寸具有明显的双峰特征。从能量角度分析发现，成坑体积、坑顶面积和最大深度随粒子动能在双对数坐标系下线性增长。基于图像处理方法获得了冲击坑周边主要矿物内部裂纹分布随冲击速度和次数增加的分形维数变化规律。破岩效果表明，增大粒子冲击速度和冲击次数能有效扩大岩石冲击坑的损伤范围，但冲击速度的影响程度显著大于冲击次数。

Experimental study on mesoscopic damage and fragmentation characteristics of hard rock under repeated particle impacts

Particle impact, a new drilling technology, has been applied in drilling and gas and oil exploitation. Also, it is considerably promising as an assisting rock breakage method for the excavation of tunnels in extremely hard rocks. In this paper, an experimental study was conducted to investigate the effects of particle impact number, particle strength, and particle impact velocity on the damage and fracture characteristics of surface crater in extremely hard granite. The three-dimensional morphology, rock fragment distribution, and fracture properties in the crater were quantitatively analyzed. The results indicate that the maximum depth of the crater increases in a parabolic way, while both the volume and surficial area of the crater grow linearly with the impact number. Moreover, the crater volume first increases and then decreases with the particle impact velocity, with a critical velocity of nearly 82.5 m/s. In addition, the mechanism difference of mesoscopic fragmentation inside and outside the crater center causes the double-peak characteristics of average size of fragments. The increase of volume, surficial area, and maximum depth of the crater are in linear relation to the kinetic energy of impacting particles in the double logarithmic coordinate. The fractal dimension variation trend of internal crack distribution in main minerals around the crater under different impact velocities and numbers were obtained through image-processing method. The experimental results manifest that the damage scale of rock crater is enlarged through improving particle velocity or impact number, while the former exerts a more significant effect.