Abstract:
The mineral resources of our country's cold regions are plentiful. As the pace of resource development in high-cold areas gradually intensifies, a number of geotechnical engineering issues in cold regions have become increasingly prominent. The investigation of the damage evolution mechanism of rocks under freeze-thaw conditions is of significant importance for the construction of geotechnical engineering in cold regions and disaster prevention and control. In order to study the damage deterioration law of the banded magnetite quartzite (BMQ) under freeze-thaw, mechanical and acoustic emission (AE) tests were carried out on BMQ under the longest freeze-thaw cycle of 280 times, the mechanical performances and AE characteristics were obtained. Combined with the theory of freeze-thaw damage, the proper freeze-thaw damage mechanism of BMQ was further investigated, Meanwhile, to establish a damage constitutive model of BMQ based on the AE characteristics of the high (freeze-thaw cycle≥70 times), low (dry, water-saturated, freeze-thaw cycle≤40 times) freeze-thaw cycles. The damage models of high (freeze-thaw cycle≥70 times) and low (dry, full of water, freeze-thaw cycle≤40 times) freeze-thaw cycles were established based on the AE parameters. The results as follow The peak strength, modulus of elasticity, AE impact number, cumulative ringing count, and cumulative energy of the low freeze-thaw cycle BMQ were significantly higher than those of the high freeze-thaw cycle rock samples. Before and after 40 cycles of freeze-thaw cycles, the single b-value of the rock samples showed a tendency of decreasing and then increasing. With the increase of freeze-thaw cycles, the decrease of the impact number of the large magnitude was higher than that of the small magnitude. The freeze-thaw damage mechanism of BMQ with low freeze-thaw cycle was dominated by the first type of freeze-thaw damage theory, while the high freeze-thaw cycle was jointly dominated by the first and the second type of freeze-thaw damage theories. The brittle damage mode dominates the low freeze-thaw cycle BMQ, while the damage mode of the high freeze-thaw cycle rock samples was transitioned from brittleness to ductility. The coupling relationship of the damage parameters of BMQ under low and high freeze-thaw cycle had been established based on the AE cumulative ring counts , the coupled relationship of damage parameters under the low and high freeze-thaw cycle had been deduced as well. The freeze-thaw damage models of BMQ under low and high freeze-thaw cycles were established and preliminarily verified.