Experimental study on damage mechanism of banded magnetite quartzite under freeze-thaw

YAN Jiaju; SHAO Guoliang; XIA Dong; JIA Yufei

doi:10.12438/cst.2024-0374

Abstract：The mineral resources of our country's cold regions are plentiful.As the pace of resource development in high-cold areas gradu-ally 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 engin-eering 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 prop-er 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 de-creasing and then increasing.With the increase of freeze-thaw cycles,the decrease of the impact number of the large magnitude was high-er 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.