含雁行裂纹砂岩静态加载速率效应实验研究

摘要

为研究裂隙岩体的静态加载速率效应,以含预制雁行裂纹砂岩为实验对象,测试了不同加载速率下试样的力学性质、破裂模式、能量耗散及声发射响应特征,综合声发射定位和裂纹扩展演化录像,分析了裂纹扩展演化过程及加载速率效应机制.结果表明:①裂隙砂岩受载过程存在着明显的静态加载速率效应.随着加载速率的升高,试样峰值强度、峰值应变、起裂应力、峰值处积累的弹性能和声发射计数峰值均逐渐增大但增幅放缓,弹性模量呈现出先增大后减小趋势,累计声发射总计数则逐渐减小.②试样新裂纹的起裂萌生均对应着应力的局部下降、耗散能的突升及声发射的高值响应.③加载速率较小时,试样沿一条预制裂纹扩展、滑移而形成剪切型破坏;当加载速率较大时,试样最终破坏模式为裂纹岩桥贯通,并由裂纹外端沿与加载方向平行扩展而成的拉破坏.研究结果为深入认识煤岩动力灾害的力学响应机制及揭示其演化过程提供了有益的参考.%To investigate the static loading rate effects on the sandstone specimen with fissures,the mechanical property,failure mode,energy dissipation and acoustic emission (AE) response characteristics of sandstone specimen containing pre-existing echelon cracks are tested in the laboratory under different loading rates.Based on the AE location technology and picture recording results,the evolution process of crack propagation and the loading rate mechanism are analyzed.The results show that:① There are significant static loading rate effects on sandstone specimen containing parallel echelon cracks under uniaxial compression.With the increase of loading rates,the uniaxial compressive strength,peak strain,initiation stress,the elastic energy at the peak stress and the peak AE counts gradually increase but the increase rate slows down.The elastic modulus shows the trend of first increasing and then decreasing.And the total number of accumulative AE counts shows a decreasing trend.② The initiation of each new crack in the specimen corresponds to the stress drop in the stress-strain curve,the sudden rise of the dissipation energy and the high values response of the AE signals.③ The specimens extend and slip along a pre-existing crack,and the shearing failure modes are formed at low loading rates.When the loading rates become larger,the final failure are tensile failure modes that the rock bridge between the two cracks links,and the outer edges of the pre-existing cracks extend to the upper and lower ends of the specimen along the loading direction.The results can provide a useful reference for further understanding on the mechanical response mechanism and revealing its evolution process of coal or rock dynamic disasters.