砂质泥岩三轴卸荷流变力学特性试验研究

流变对工程岩体的长期变形稳定具有十分重要的影响，但目前关于卸荷流变的试验研究中通常只考虑恒轴压卸围压的应力路径，与隧洞开挖过程中围岩的应力调整过程存在一定的差距。以砂质泥岩为试验研究对象，设计进行了加轴压卸围压和恒轴压卸围压条件下的分级卸荷流变试验。试验结果表明：恒轴压卸围压和加轴压卸围压方案下岩样的流变变形趋势总体一致，但相同初始围压条件下，加轴压卸围压试样破坏的围压相对较高，偏应力相对较大，但长期强度与破坏应力的比值相对较小；在围压卸载至岩样临近破坏时，加轴压卸围压方案下岩样的流变应变增长速率明显较快，试样破坏的更加突然；恒轴压卸围压条件下岩样的破坏形态相对简单，一般只存在一条完整的剪切破坏面，而加轴压卸围压条件下岩样的破坏形态要复杂得多，除了控制性的剪切破坏面之外，还伴随有一定数量的次生剪裂纹和张拉裂纹，而且初始围压越大，试样的次生裂纹越多。因此，在隧洞围岩长期变形稳定分析过程中，单纯的恒轴压卸围压流变试验不能满足工程实际需求，应该尽量丰富岩石力学试验的应力路径，以便较好地模拟工程岩体应力的实际变化过程，研究成果为隧洞围岩的长期变形稳定性研究提供了较好的研究思路。

Experimental research on unloading triaxial rheological mechanical properties of sandy mudstone

Rheology has extremely significant influence on the long-term deformation and stability of engineering rock mass. Current experimental research on unloading rheology only considers the stress path under unloading confining pressure with the constant axial stress, however it is different from the process of stress adjustment in surrounding rock during tunnel excavating. Stepwise unloading rheological tests are conducted on sandy mudstone samples which are under unloading confining pressure with the axial compression or with the constant axial stress. The results show that the rheological deformation trends of rock samples under both unloading confining pressure are generally consistent. At the same initial confining pressure, the failure confining pressure under axial compression and the deviatoric stress are relatively higher than that under constant axial stress, but the ratio of long-term strength to failure stress is opposite. When the confining pressure unloads reach up to the point where the rock sample approaches failure, the growth rate of rheological strain under axial compression obviously becomes faster than that under constant axial stress, and the failure occurs more suddenly. The failure modes of rock samples under constant axial stress usually appear as one complete shear failure plane. By contrast, the failure modes of rock samples under axial compression are more complicated with a certain amount of secondary shear cracks and tension cracks, in addition to the controlled shear failure plane. Moreover, the secondary cracks increase with the increase of initial confining pressure. Therefore, the unloading confining pressure with the constant axial stress seems difficultly satisfy the requirement of engineering projects undergone a long-term deformation and stability of surrounding rock. The stress paths of tests should be conducted in more detail to simulate the actual stress change process of engineering rock mass. The results provide insights into the research on long-term deformation and stability of underground surrounding rock.