三轴卸荷损伤砂岩单轴再承载力学特性及其破坏机制

Uniaxial re-bearing mechanical characteristics and failure mechanism of triaxial unloading-damaged sandstone

深部煤炭资源开采面临着高应力的地质环境和岩体开挖卸荷的工程环境,卸荷损伤岩体再承载力学特性及破坏机制研究对于揭示深部岩体失稳破裂规律具有重要意义。通过控制三轴加载卸荷点制备损伤砂岩试件,采用RMT-150C岩石力学加载系统和东华DHDAS应力-应变采集系统,监测三轴卸荷及单轴再加载过程中试件的横向应变和轴向应变。试验结果表明:根据加载前后波速差值,可将卸荷岩体分为压密岩体、低损岩体和高损岩体3类;随着卸载应力水平的升高,损伤砂岩由塑-弹-塑性体变形特征过渡为塑-弹性体变形特征最后转变为弹-黏性体变形特征;压密岩体单轴再加载裂纹体积应变曲线与标准砂岩基本一致,低损岩体弹性变形阶段明显缩短,高损岩体经历极小变形就发生破坏;压密岩体呈现Y型斜面剪切破坏特征,低损岩体在卸荷阶段出现的纵向裂缝和裂隙基础上发育并贯通形成主控裂纹造成破坏,高损岩体在Y型斜面剪切破裂基础上发育为X型斜面剪切破坏;建立了单轴压应力下裂纹力学分析模型,明确了岩石裂纹断裂角θ与裂纹角β和裂纹面摩擦系数f之间的关系。

Mining deep coal resources involves high stress geological environment and rock excavation unloading engineering environment.Research on the re-bearing capacity characteristics and damage mechanism of unloading-damaged rock is crucial for revealing the instability and rupture behavior of deep rock body.The damaged sandstone specimens were prepared by controlling the unloading point during triaxial loading.Transverse and axial strains of the specimens were monitored using the RMT-150C rock mechanics loading system and the Donghua DHDAS stress-strain acquisition system during triaxial unloading and uniaxial reloading.The test results show that according to the wave velocity differences before and after loading,the unloaded rock body can be classified into three categories:compact rock body,low-loss rock body and high-loss rock body.With the increase of unloading stress level,the damaged sandstone transitions from plastic-elastic-plastic deformation to plastic-elastic deformation,and finally to elastic-viscous deformation.The crack volume strain curve of the compact rock body during uniaxial reloading is basically the same as that of the standard sandstone.The elastic deformation stage of the low-loss rock body is obviously shortened,while the high-loss rock body fails after minimal deformation.The compact rock body exhibits Y-type diagonal shear damage characteristics.The low-loss rock body develops and penetrates through longitudinal cracks and fissures formed during the unloading phase,leading to master cracks causing damage.The high-damage rock body develops X-type diagonal shear damage on the basis of Y-type diagonal shear rupture.A mechanical analysis model of cracks under uniaxial compressive stress was established.The relationship between rock crack fracture angleqand crack angleband friction coefficient f of crack surface was elucidated.