Energy Characteristics and Damage Constitutive Model of Frozen Sandstone under Triaxial Compression

To study the energy characteristics and damage laws of frozen rock during mine freezing, a triaxial compression test and synchronous acoustic emission test of frozen sandstone are conducted. The results show that (1) the peak stress of frozen sandstone is more than as thrice as that of sandstone at 20 degrees C. According to the elastic energy conversion rate, two stress thresholds are determined, and the peak stress is combined to divide the frozen sandstone damage section. When the stress is in the range of 0-sigma(eb), the increase rates of the dissipation energy (U-d) and acoustic emission cumulative energy (AECE) of the frozen sandstone are significantly less than those of the sandstone at 20 degrees C. The total input energy (U), elastic energy (U-e), and U-d at the peak stress of frozen sandstone are more than as twice as those of sandstone at 20 degrees C. As the negative temperature of the sandstone decreases, U, U-e, and the elastic energy conversion rate at the peak stress slightly increase. (2) The AECE of the 20 degrees C sandstone at the peak stress is approximately 1/2 the AECE(max). The AECE of the frozen sandstone at the peak stress accounts for approximately 1/5 the AECE(max). As the negative temperature decreases, the AECE(max) of the sandstone increases. (3) As the confining pressure of frozen sandstone increases, U, U-e, and U-d at the peak stress increase, the elastic energy conversion rate decreases, and AECE(max) significantly increases. For frozen sandstone under different confining pressures, AECE at the peak stress accounts for 11%-25% of AECE(max), and the proportion increases with increasing confining pressure. (4) AECE is used to define the damage variables, and a constitutive model of frozen sandstone is obtained. Before the peak stress, the results of the constitutive model are in agreement with the test results. The two damage evolution curves of frozen sandstone based on U-d and AECE can describe the damage evolution process.