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冻融作用下条带状磁铁石英岩损伤机理试验研究

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

  • 摘要: 我国寒区矿产资源丰富,随着高寒地区资源开发强度的逐渐加大,众多寒区岩土工程问题日益突出,研究冻融作用下岩石损伤演化机理,对寒区岩土工程建设和灾害防治具有重要意义。为探究冻融作用对岩石的损伤劣化规律,以研山铁矿东帮边坡条带状磁铁石英岩为研究对象,对冻融区间‒20,20℃、最长冻融周期为280次的条带状磁铁石英岩开展了力学与声发射试验,获得该岩石不同冻融周期的力学、声发射特征参数。结合冻融损伤理论,进一步探究适用于该岩石的冻融损伤机理,建立基于声发射特征参数的高(冻融周期≥70次)、低(干燥、饱水、冻融周期≤40次)冻融周期的损伤本构模型。研究结果表明:低冻融周期条带状磁铁石英岩的峰值强度,弹性模量,声发射撞击数、累计振铃计数、累计能量的降低幅度均明显高于高冻融周期的岩样;冻融40周期前后,岩样单一b值呈先降后升趋势;随冻融周期的增加,大震级撞击数的下降幅度高于小震级;低冻融周期岩样的冻融损伤机制以第1类冻融损伤理论为主导,高冻融周期岩样的冻融损伤机制为第1和第2类冻融损伤理论共同主导;低冻融周期岩样以脆性破坏模式为主,高冻融周期岩样的破坏模式由脆性逐渐向延性过渡;基于声发射累计振铃计数,建立了高、低冻融周期岩石的损伤变量耦合关系式,推导了高、低冻融周期岩石的冻融损伤模型,并对其进行了初步验证。

     

    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.

     

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