底板硬岩多轴条件下的力学特性和冲击倾向性

Mechanical properties and impact tendency of hard floor rock under multiaxial conditions

为研究深部煤矿顶底板围岩在高应力下的冲击危险性,以跃进煤矿为工程背景,取自23092工作面的底板硬岩作为试验对象,应用真三轴试验机进行了一系列多轴(常规三轴和真三轴)条件下的压缩力学特性试验,部分试验还同步了破坏过程声发射信号测量。借助光学显微镜和场发射扫描电镜辅助分析试样微观特性表征。多轴压缩力学试验表明23092工作面底板硬岩具有明显弹脆性变形破坏行为,底板硬岩在单轴压缩情况下的脆性程度最高,中间主应力与脆性破坏指数负相关。最小主应力恒定时,中间主应力增加情况下的岩样的全应力-应变曲线、宏观破坏模式、岩样破裂角、脆性指数以及破坏岩样的SEM图像的变化特征均表明底板硬岩的脆性破坏特征与应力状态有关,即中间主应力增加促进其脆性破坏行为。底板硬岩在多轴应力状态下表现出峰值强度较大离散性,这与成岩过程中软弱矿物夹杂汇聚造成的岩石均质性差异有关。底板硬岩的冲击倾向性受真三向应力状态影响,最小主应力接近零的巷道底板表层附近硬岩表现为无或弱冲击危险性,但在中间主应力较高的深层硬岩则表现强冲击危险性,且随中间主应力增加而增强。多轴条件下压缩破坏的声发射信号具有前兆释放性,声发射信号伴随峰后多阶段破裂显著增强。

In order to study the impact hazard of surrounding rock of roof and floor in deep coal mine under high stress conditions,the hard floor rock at the Yuejin Coal Mine 23092 working face is taken as a test object,and a series of compression mechanical properties tests under multiaxial(conventional and true triaxial)conditions are carried out.In some experiments,acoustic emission system has been employed to measure the fracture signal.For the analysis of the test results,the optical microscope and the field emission scanning electron microscope are used to represent the internal feature.It has been shown that the hard floor rock at the 23092 working face has shown obvious elastic brittle deformation and failure behavior.The brittle degree of the hard floor rock is the highest under uniaxial compression condition,and the intermediate principal stress is negatively related to the brittleness index.The whole stress-strain curve,macroscopic failure mode,fracture angle,brittleness index of the rock sample and the change characteristics of the SEM image of the failure rock sample all show that the brittleness failure characteristics of the hard floor rock are related to the stress state.That is to say,the increase of the intermediate principal stress promotes its brittleness failure behavior when the minimum principal stress is constant and the intermediate principal stress increases.Under the condition of multi axial stress,the peak strength of hard floor rock is discrete,which is related to the difference of rock homogeneity caused by the convergence of weak mineral inclusions in the process of diagenesis.The impact tendency of hard floor rock is affected by true three-dimensional stress state.The hard rock near the surface of roadway floor with minimum principal stress close to zero shows no or weak impact risk,but the deep hard rock with high intermediate principal stress shows strong impact hazard,and increases with the increase of intermediate principal stress.Acoustic emission signals with compression and destruction under multi-axial conditions have a precursory release feature,and the acoustic emission signals are significantly enhanced in the post-peak multi-stage rupture.The research results have some reference values for the further research of deep coal rock deformation and failure mechanism and evaluation of impact tendency in deep coal mines.