石灰岩脆性损伤演化和声发射特征研究

Study on Brittle Damage Evolution and Acoustic Emission Characteristics of Limestone

脆性是深部岩体最重要的力学性质之一。为研究石灰岩脆性损伤演化机制,开展了单轴压缩下石灰岩声发射试验,分析了脆性指数与损伤变量和声发射b值的关系。结果表明:(1)石灰岩裂纹闭合应力、裂纹起始应力、损伤应力占峰值应力的比值分别为31.3%、43.0%、85.5%;(2)石灰岩脆性指数平均为0.32,均方差为0.009,随脆性指数上升,特征应力对应的损伤变量逐渐减小,损伤变量由“正比例函数”增长逐渐变为“凹形幂函数”增长,临界破坏阶段存在损伤加速现象;(3)在单轴压缩条件下,随脆性指数上升,石灰岩剪切破坏减弱、张拉破坏增强,脆性指数能够较好地表征其破坏形式;(4)石灰岩声发射累计振铃计数、累计能量和累计幅值与时间曲线存在明显的4个阶段:微增期、平静期、陡增期、骤降期,且平静期幅值均小于80 dB,曲线总体呈台阶状上升趋势。脆性指数越大,平静期越长,陡增期越短,b值突点对应应力与峰值应力比值越大;(5)b值曲线呈先上升后下降趋势,b值突点均在平静期结束点之前,这两点均能准确预警石灰岩失稳破坏,随脆性指数上升,b值突点出现越晚,越接近峰值。研究成果可为围岩稳定性控制和动力灾害监测预警提供重要参考。

Brittleness is one of the most important mechanical properties in deep rock mass.In order to study the brittle damage evolution mechanism of limestone,the acoustic emission test of limestone under uniaxial compression was carried out,and the relationship between brittleness index and damage variable and b-value was analyzed.The results show that:(1)The ratios of crack closure stress,crack initiation stress and damage stress to peak stress in limestone are 31.3%,43.0%and 85.5%,respectively.(2)The average brittleness index of limestone is 0.32,and the mean square error is 0.009.With the increase of brittleness index,the damage variable corresponding to the characteristic stress gradually decreases,and the damage variable gradually increases from‘proportional function’to‘concave power function’.The damage acceleration phenomenon exists in the critical failure stage.(3)Under the condition of uniaxial compression,with the increase of brittleness index,the shear failure of limestone decreases and the tensile failure increases,and the brittleness index can better characterize its failure mode.(4)There are four obvious stages in the cumulative ringing count,cumulative energy,cumulative amplitude and time curve of acoustic emission in limestone:slight increase period,quiet period,steep increase period and sharp decrease period.The amplitude of quiet period is less than 80 dB,and the curve shows a step-like upward trend.The larger the brittleness index,the longer the quiet period,the shorter the sharp increase period,and the greater the ratio of the stress corresponding to the b value to the peak stress.(5)The b-value curve shows a trend of rising first and then falling,and the b-value abrupt points are all before the end of the quiet period.These two points can accurately warn the instability and failure of limestone.With the increase of brittleness index,the b-value abrupt point appears later and closer to the peak.The research results provide important reference for surrounding rock stability control and dynamic disaster monitoring and early warning.