Experimental research on deformation and failure characteristics of coal by staged cyclic loading and unloading
LI Shugang,LIU Sibo,LIN Haifei,SHUANG Haiqing,LI Leiming,YU Hanxu,LUO Rongwei
瓦斯抽采钻孔在采动影响下所处的应力状态比较复杂,随着工作面的推进,经历复杂的加载和卸载共同作用,易导致抽采钻孔失稳破坏。为深入研究采动影响下煤体钻孔的变形破坏特征,通过开展单调加载及分级循环加卸载试验,分析不同加载路径下试样的强度特征,并结合数字散斑技术(XTDIC)分析试样单轴压缩过程中裂纹扩展及孔周位移演化规律,通过布置“虚拟引伸计”分析试样局部化带位移演化特征。结果表明:与单调加载路径相比,分级循环加卸载路径下试样的抗压强度减小,减小幅度为4.59%;分级循环加卸载路径下,含钻孔试样的最终破坏是由远场裂纹与钻孔两侧的剪切裂纹贯通形成宏观破裂带导致的,不同加载路径下试样破坏模式均为拉剪复合破坏,破坏形态呈“X”状;试样加载顶点与卸载低点的张拉、错动位移随着循环次数增加逐渐增大,呈波动上升趋势,并且在时间上滞后于应力变化;孔周位移测点层位越高,试样加载至相同时刻的位移越大;分级循环加卸载路径下,试样卸载阶段的测点位移有轻微恢复现象,最大恢复量为0.149 mm,位移随时间增长表现为“台阶式”递增现象。
The stress state of the gas drainage borehole under the influence of mining is relatively complicated. As the working face advances, it experiences a complex combination of loading and unloading, which may easily lead to instability and destruction of the drainage boreholes. In order to investigate the deformation and failure characteristics of coal boreholes under the influence of mining, monotonic loading and multistage cyclical loading and unloading tests were carried out to analyse the strength characteristics of the samples under different loading paths. Crack growth and the evolution of the displacement around the borehole during uniaxial compression of specimens were analyzed by using digital scatter technique (XTDIC)and the displacement evolution characteristics of the localized zone of the sampleswere analyzed by arranging the“virtual extensometer”. The results show that the compressive strength of the specimen is reduced by 4.59% under multistage cyclical loading-unloading path compared with monotonically loaded specimen. Under the multistage cyclical loading-unloading paths, the final failure of the specimens containing boreholes is caused by the penetration of the far-field cracks and the shear cracks on both sides of the borehole to form a macroscopic fracture zone.The failure mode of the specimens under different loading paths is tensile-shear composite damage with an“X”shape. The tension and misalignment displacement of the specimen at the top point of loading and the low point of unloading gradually increases with the number of cycles, presenting a fluctuating upward trend, and lagging behind the stress change in time.The higher the level of the displacement measurement point around the hole, the greater the displacement of the specimen loaded at the same time. Under the multistage cyclical loading and unloading path, the displacement of the measured point during the unloading stage of the specimen has a slight recovery, the maximum recovery is 0.149 mm, and the displacement increases with time in a“stepped”incremental phenomenon.
staged cyclic loading and unloading; crack evolution; localized zone displacement; virtual extensometer; drainage borehole
主办单位:煤炭科学研究总院有限公司 中国煤炭学会学术期刊工作委员会