关键词: 盐岩, 单轴, 蠕变, 声发射, 分形维数, 损伤变量

Abstract: 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.

Key words: salt rock, uniaxial, creep, acoustic emission, fractal dimension, damage variable