冲击荷载作用下含双孔洞裂纹石灰岩动态断裂行为

Dynamic fracture behavior of limestone specimens containing double holes and crack under impact loading

深入了解不同孔洞缺陷结构对岩石动态力学特性和断裂行为的影响,对于巷道支护设计、岩体工程稳定性评价以及冲击地压动力灾害防治等均具有重要的理论指导意义。为研究含不同孔洞缺陷石灰岩试样在冲击荷载下的动态断裂行为,利用分离式霍普金森压杆(SHPB)冲击加载系统,对含双孔洞裂纹石灰岩试样进行冲击条件下的断裂特性测试,并采用高速摄像仪对动态裂纹萌生、扩展、贯通直至试样破坏全过程进行了记录,结合图像处理方法进一步分析了冲击荷载作用下含双孔洞裂纹石灰岩的动态抗压强度、动态变形模量、破坏模式和裂纹扩展行为。研究表明:峰值应力处试样破坏的峰值应变在0.00297~0.00493变化,孔洞间距的非对称增长对石灰岩试样峰值强度具有较大弱化影响,非对称孔洞缺陷的间距越大,其对试样的峰值强度弱化程度越高;当孔洞缺陷呈现为非对称状态时,由于受力不均易较早发生压缩破坏。石灰岩试样双孔洞缺陷的形状、间距和非对称性均对其动态抗压强度具有显著影响。石灰岩试样下方的孔洞缺陷对其主裂纹发育具有显著影响,使得初始拉伸裂纹扩展方向产生偏转,试样最终破坏主模式为剪切-拉伸复合断裂。在石灰岩试样的裂纹发育类型中,类型Ⅴ和Ⅵ的远场拉伸和剪切裂纹较为常见。此外,考虑扩展路径分形效应的裂纹速度为表观裂纹扩展速度的1.01~1.17倍。当孔洞缺陷呈非对称分布且间距较大时,最终形成的裂纹数量较少,裂纹扩展速度降低,且更有利于抑制岩石表面的岩屑剥落现象。

In-depth understanding of the influence of different hole defect structures on the dynamic mechanical proper-ties and fracture behavior of rocks is an important theoretical guidance for the design of roadway support,rock engineer-ing stability evaluation and mine pressure bump dynamic disaster prevention.The dynamic fracture behavior of limestone specimens containing different hole defects under impact loading was investigated.The fracture characteristics of the lime-stone specimens containing double-hole and crack were tested under impact conditions by using a split Hopkinson pres-sure bar(SHPB)impact loading system.The whole process of dynamic crack initiation,propagation and penetration was recorded by the high-speed camera.The dynamic compressive strength,dynamic deformation modulus,failure mode and crack extension behaviour of the double-hole limestone under impact loading were further analyzed by combining image processing method.The results show that the peak strain of specimen varies from 0.00297 to 0.00493 when the double-hole defects appear asymmetric.This is due to uneven stresses prone to earlier compression damage.The asymmetric growth of the hole spacing has a greater weakening effect on the peak strength of limestone specimens.The larger the spa-cing of the asymmetric hole defects,the higher the degree of weakening of the peak strength of the specimens.The shape,spacing and asymmetry of the double hole defects in the limestone specimens all have the significant effect on dynamic compressive strength.The hole defects in the lower part of the limestone specimen have a significant effect on the propagation of the primary crack.This deflects the direction of initial tensile crack extension,resulting in the main mode of damage being a shear-tensile composite fracture.Among the damage modes of the limestone specimens,far-field tensile and shear cracks of types V and VI are more common.In addition,the cracking velocity considering the extension path fractal effect is 1.01-1.17 times of the apparent crack extension velocity.When the hole defects are asymmetrically dis-tributed and widely spaced,the final number of cracks formed is smaller,the crack expansion velocity is reduced,and it is more favorable to suppress the rock chip flaking phenomenon on the rock surface.