盐岩单轴蠕变声发射特征及损伤演化研究

Creep acoustic emission and damage evolution of salt rock under uniaxial compression

为研究盐岩在长历时蠕变过程的声发射特征规律与损伤演化过程,采用四川大学大型程控流变仪和PAC Sensor highway Ⅱ型声发射监测仪器对盐岩进行了为期约1a的单轴蠕变声发射试验,分析了盐岩长历时蠕变过程应变规律与声发射试验结果,探讨了盐岩全蠕变损伤演化过程。试验结果表明,盐岩在为期约1 a的蠕变时间内经历了初始衰减蠕变阶段、稳态蠕变阶段、加速蠕变阶段,其中稳态蠕变速率基本维持在6×10^(-5)d^(-1);盐岩全蠕变过程声发射各特征参数规律与蠕变应变趋势基本一致,呈活跃-平静-活跃趋势,同时根据声发射参数特征曲线可以预判盐岩进入加速蠕变阶段在300 d之时,比由应变曲线(320d)判断更为提前,为储气库工程建设提供室内试验依据;根据声发射时空演化特征揭示了盐岩长历时蠕变损伤破坏路径是从端部-中部-整部的形式;基于声发射振铃计数特征参数计算的损伤变量变化趋势与蠕变应变趋势一致,而盐岩蠕变全过程声发射分形维数呈下降-波动-上升的趋势,表征声发射经历了一个从无序到有序再到无序的过程,且与蠕变速率曲线变化一致,分形维数的拐点与声发射提前预判加速蠕变拐点节点相一致,分形维数变化与损伤变量率变化趋势基本一致,进一步分析表明声发射分形维数值基本在2上下波动,损伤变量率基本稳定在0.002 d^(-1)周围。

To investigate the acoustic emission(AE) characteristics and damage evolution process of salt rock during the long creep process, uniaxial creep AE tests were carried out by using a large-scale programmed rheometer and the PAC Sensor-highway Ⅱ AE monitoring instrument at Sichuan University. The strain law and AE test results of the long creep process of salt rock were analysed, and the evolution process of the whole creep damage was discussed in detail. The results show that the salt rock undergoes an initial attenuation creep stage, a steady creep stage and an accelerated creep stage during the creep period of about one year, in which the steady creep rate is basically maintained at 6×10-5 d-1. The variation of characteristic parameters of AE in the whole creep process is basically consistent with the creep strain trend, showing an "active-quiet-active" trend. According to the AE parameter characteristic curve, the salt rock can be predicted to begin the accelerated creep stage at 300 days, and it is more accurate than the creep strain trend line, which provides experimental fundamentals for the construction of the gas storage. According to the characteristics of temporal and spatial evolution of AE, the damage path of the long-duration creep damage of the salt rock is from the form of "end-central-whole part". The change trend of the damage variable based on the AE ringing counts is consistent with the creep strain trend. Moreover, the fractal dimension of AE in the whole process of the salt rock shows a "decreasing-fluctuating-rising" trend, which indicates that the AE undergoes a process from disorder to order and then to disorder, and changes with the creep rate curve consistent. The inflection point of fractal dimension is consistent with that of AE in predicting an accelerated creep inflection point, and further analysis shows that the fractal dimension of AE is basically fluctuating up and down at the value of 2. The damage variable rate is basically stable at around 0.002 d-1.