基于AE统计模型的砂岩蠕变试验研究

Experimental Study on Creep Damage of Sandstone Based on Acoustic Emission Tests

为分析水溶液对砂岩蠕变特性的影响,利用RLJW-2000岩石流变伺服仪对3种含水率下的砂岩进行了单轴长期力学行为研究,并利用PAC声发射(AE)监测仪对砂岩试验全过程进行声信号采集。试验结果表明:砂岩在长期荷载下,表现出应变硬化特征,有明显的蠕变稳态阶段,伴随加载的进行,蠕变速率随之增大;随着含水率的增加,相同应力等级下的蠕变速率随之增大。振铃计数率与蠕变速率具有相同的变化趋势,且累计振铃计数-时间曲线与应变-时间曲线两者走势基本相同。在假设试验材料服从Weibull统计分布的前提下,通过AE事件数表示岩石的损伤程度,推导出了基于AE事件点的损伤演化方程,相同应力水平下,高含水率砂岩内部损伤发展较低含水率快。比较蠕变曲线和损伤变量曲线的加速临界时间点,发现基于损伤变量得到的临界时间点相对蠕变加速时间点较为提前,说明利用声发射来预测蠕变破坏时间更为准确,这对于实际工程中的灾害防治工作有着重要作用。

To investigate the influence of aqueous solution on the creep property of sandstone,we carried out longterm uniaxial compression creep tests on sandstone specimens of different moisture content by RLJW-2000 rock microcomputer-controlled rheology servo; and meanwhile conducted acoustic tests by SH-2 acoustic emission monitor.Test results revealed that sandstone displayed obvious strain hardening characteristics with apparent creep steady phase. At given moisture content,the creep rate of sandstone increased as stress increased; and under the same stress level,creep rate increased also as stress increased. Moreover,ring count rate and creep rate shared the same trend: the time-history curves of accumulative ring count and strain are similar in general. Assuming that the test materials obey Weibull distribution,we derived a damage evolution equation based on acoustic emission event point,and found that damage in sandstone of high moisture content developed faster than that of low moisture content under the same stress level. By comparing the critical acceleration point of creep curve and damage variable curve,we also found that acoustic emission is more accurate in predicting the time of creep.