静水压下原生组合煤岩动力学破坏特征

Dynamic failure characteristics of primary coal-rock combination under hydrostatic pressure

深部巷道围岩软弱、裂隙发育,开采扰动影响下易导致动力灾害,其中煤岩组合体整体失稳破坏是诱发灾害的关键因素之一。为探究冲击载荷下原生组合煤岩体的动力学破坏特征,借助分离式霍普金森杆系统及高速摄像机,以原煤、原生组合、人工组合煤岩为研究对象,探究不同静水压、应变率下煤岩动态应力应变、裂纹演化、破碎特征,并采用宏观破碎分形及细观电镜扫描研究煤岩变形破坏特征。研究表明:①原煤、原生组合、人工组合煤岩的动态应力−应变呈显著非线性,原生煤岩的塑性阶段近似“塑性平台”。②冲击载荷下,煤岩动抗压强度的应变率效应显著;原煤、原生组合煤岩的动抗压强度与静水压呈先增后减趋势,静水压作用(低压强化、高压弱化)的临界值分别为8、10 MPa,人工组合煤岩与静水压呈正相关趋势。③冲击荷载下,原生及人工组合煤岩的裂隙起裂均发生于远离煤岩交界面的煤组分区域;组合煤岩交界面显著影响试样变形破坏行为,当冲击速度≥10 m/s,原生组合煤岩均可发生煤岩组分的整体失稳破坏,而相同扰动下人工组合煤岩仅发生煤组分破坏,仅当冲击速度≥14 m/s,裂纹的尖端应力大于煤岩强度,可贯通人工交界面,导致整体破碎;原生交界面对试样裂纹贯通具有“导向作用”,易诱发裂纹扩展形成宏观破裂面。④原煤、原生及人工组合煤岩破碎程度随冲击速度的增大而增大,破碎粒径趋于粒状、粉末状;相同扰动下,3类煤岩中煤组分的破碎程度:原生−煤组分>人工−煤组分>原煤。

The surrounding rock of deep roadway is weak and the fissures are developed.Under the influence of mining disturbance,it is easy to cause dynamic disasters and the overall instability failure of coal rock combination is one of key factors inducing disasters.In order to explore the dynamic damage characteristics of the primary combined coal rock body under impact load,with the help of the split Hopkinson pressure bar and high-speed camera,raw coal,artificial combination and primary combination of coal rock are studied.Based on different hydrostatic pressure and strain rate conditions,this study explores the dynamic stress-strain,crack evolution and fracture fractal characteristics of coal rock and explores the deformation and failure characteristics of coal rock using macroscopic fracture fractal and microscopic electron microscope scanning.The study shows that①the dynamic stress-strain of raw coal,artificial combination and primary combination of coal rock is significantly nonlinear and the plastic stage of primary coal rock is similar to“plastic platform”.②Under impact load,the strain rate effect of dynamic compressive strength of coal rock is significant and the dynamic compressive strength and hydrostatic pressure of raw coal,primary combined coal rock show a trend of first increasing and then decreasing.The critical values of hydrostatic pressure(low pressure strengthening and high pressure weakening)are 8 MPa and 10 MPa and the artificial combined coal rock and hydrostatic pressure show a positive correlation trend.③Under the impact load,the crack initiations of primary and artificial combined coal rock occur in the coal composition area far from the interface of coal rock.The combined coal-rock interface significantly affects the deformation and failure behavior of the sample and when the impact velocity≥10 m/s,the overall instability failure of coal rock components can occur in the original combined coal rock,while only the coal component failure occurs in the artificial combined coal rock under the same disturbance.Besides,only when the impact velocity≥14 m/s,the tip stress of the crack is greater than the strength of the coal rock,which can penetrate the artificial interface and lead to the overall crushing.The original interface has a“guiding effect”on the crack penetration of the sample,which is easy to induce crack propagation to form a macro-scopic fracture surface.④The crushing degrees of raw coal,original coal and artificial coal rock increase with the in-crease of impact velocity and the crushing particle size tends to be granular and powder.Under the same disturbance,the degrees of fragmentation of coal components in three types of coal rocks show a relationship:primary-coal components>artificial-coal components>raw coal.