Mechanical properties and mesoscopic damage evolution of coal under liquid-nitrogen freezing at different initial temperatures
LI Botao1, 2, 3, TAN Yuxuan1, LIN Haifei4, 5*, WEI Jianping1, 2, 3, ZHANG Hongtu1, 2, 3, LI Shugang4, 5, WEI Zongyong4, 5, WANG Pei4, LUO Rongwei4, LIU Yanwei1, 2, 3
(1. School of Safety Science and Engineering, Henan Polytechnic University, Jiaozuo, Henan 454000, China; 2. State Key Laboratory Cultivation Base for Gas Geology and Gas Control, Henan Polytechnic University, Jiaozuo, Henan 454000, China; 3. State Collaborative Innovation Center of Coal Safety in Production and Clean-efficiency Utilization, Henan Polytechnic University, Jiaozuo, Henan 454000, China; 4. College of Safety Science and Engineering, Xi'an University of Science and Technology, Xi?an, Shaanxi 710054, China; 5. Key Laboratory of Western Mine Exploitation and Hazard Prevention, Ministry of Education,
Xi?an University of Science and Technology, Xi'an, Shaanxi 710054, China)
Abstract：To investigate the effects of liquid nitrogen freezing on the mechanical properties and meso-damage of coal at various temperatures, uniaxial compression tests and three-dimensional full-field strain measurements were conducted on coal samples subjected to liquid nitrogen freezing across a temperature range of 25 ℃ to 65 ℃. Numerical simulations of coal undergoing liquid nitrogen freezing at different temperatures were performed using a thermal-mechanical-damage coupling model to explore the meso-damage of coal. The results indicate that liquid nitrogen freezing significantly deteriorates the compressive strength and elastic modulus of coal, with the degree of deterioration progressively increasing with higher initial temperatures. Most failures in coal samples are tensile in nature, with the locations of surface cracks aligning with zones of stress concentration. As the temperature of the coal increases, the energy consumed during the deformation and failure of the coal samples decreases, and the stress required at each stage gradually declines. When the surface of the coal sample is exposed to liquid nitrogen freezing for 0.5 minutes, the contact surface temperature drops sharply, creating a low-temperature region around the coal wall and generating high thermal stress on the surface. After 5 minutes of liquid nitrogen freezing, the surface temperature of the coal sample closely matches that of the liquid nitrogen, leading to the development of a distinct temperature gradient within the coal, a gradual reduction in generated peak thermal stress, and an expansion of the thermal stress range. Following 20 minutes of freezing, the temperature at the center of the coal sample begins to decrease, the internal temperature difference narrows, and thermal stress further diminishes while the region affected by thermal stress expands and distributes uniformly within the coal sample. The variation in the mechanical strength of coal during low-temperature freezing with liquid nitrogen can be classified into three phases: a sharp decrease phase, a slow decrease phase, and a stable phase. As the coal temperature rises, the thermal stress induced by liquid nitrogen freezing increases, resulting in more pronounced coal damage and reduced mechanical strength. The compressive strength of coal samples at 65 ℃ decreases by 48.28% after liquid nitrogen freezing, which is significantly higher than the 11.08% reduction observed in coal samples at 25 ℃. This study provides a theoretical foundation for the engineering application of liquid nitrogen fracturing and permeability enhancement technology in deep low-permeability coal seams.
李博涛1，2，3，谭宇轩1，林海飞4，5*，魏建平1，2，3，张宏图1，2，3，李树刚4，5，魏宗勇4，5，王 裴4，罗荣卫4，刘彦伟1，2，3. 液氮冻结不同温度煤体力学特性及细观损伤演化规律研究[J]. 岩石力学与工程学报, 2026, 45(6): 1757-1772.
LI Botao1, 2, 3, TAN Yuxuan1, LIN Haifei4, 5*, WEI Jianping1, 2, 3, ZHANG Hongtu1, 2, 3, LI Shugang4, 5, WEI Zongyong4, 5, WANG Pei4, LUO Rongwei4, LIU Yanwei1, 2, 3. Mechanical properties and mesoscopic damage evolution of coal under liquid-nitrogen freezing at different initial temperatures. , 2026, 45(6): 1757-1772.
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