深部砂岩三轴加卸载力学响应及其破坏特征

Mechanical response and failure characteristics of deep sandstone under triaxial loading and unloading

借助于GCTS伺服系统及微米CT扫描试验机,对深部砂岩进行高地应力状态还原下的“三阶段”加卸载应力-渗流耦合试验,得到了深部砂岩变形全过程应力-应变与渗透率演化曲线及破坏后的深部典型砂岩μCT图片,较好地表征了应力-渗流耦合下深部砂岩的力学响应行为及其破坏特征。研究表明:1)“三阶段”加卸载下的深部砂岩呈现出明显的脆-延转化特征,高卸载预设围压下的深部砂岩脆性破坏特征显著,低卸载预设围压下的深部砂岩延性破坏特征显著;2)围压效应与轴压效应对深部砂岩的强度演化规律均存在显著影响;3)围压效应与轴压效应对深部砂岩峰值渗透率演变规律亦存在一定的影响,但围压效应对深部砂岩峰值渗透率演变规律的影响程度明显弱于轴压效应;4)不同模拟深度下的深部砂岩破坏特征存在显著差异,模拟深度为1000 m与1500 m的深部砂岩表现为明显的“Y”型破坏,而模拟深度为2000 m的深部砂岩则表现为主裂纹主干型破坏。以上规律可为深部矿井巷道与硐室稳定性控制提供一定的理论依据。

Stress-seepage coupling test of deep sandstone was conducted by adopting GCTS servo system and Micro CT scanning machine under“three-stage”loading and unloading with high in-situ stress state reduction.Stress-strain and permeability response curves of deep sandstone during entire deformation process were obtained.TheμCT pictures of typical deep sandstone failure were also obtained.Meanwhile,mechanical response behavior and failure characteristics were better characterized under stress-seepage coupling.Results show that:1)the deep sandstone showed obvious brittle-ductility transformation characteristics during“three stages”with loading and unloading.The brittle failure characteristics is significant under high unloading preset confining pressure,while the ductility failure characteristics is significant under low unloading preset confining pressure.2)The confining pressure effect and axial pressure effect have large influence on strength evolution law of deep sandstone.3)The confining pressure effect and axial pressure effect have certain effect on peak permeability evolution law of deep sandstone.Furthermore,the influence degree of confining pressure effect on peak permeability evolution law was obviously weaker than that of the axial pressure effect.4)There were significant differences in deep sandstone failure characteristics at different simulated depths.Deep sandstone with simulated depth of 1000 m and 1500 m showed obvious“Y”type failure,while deep sandstone with simulated depth of 2000 m showed crack trunk failure.Above outcomes could provide theoretical basis for stability control of deep mine roadway and chamber.