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QIN L, LIU P F, LI S G,et al.Mechanical behavior of coal subjected to liquid nitrogen freeze-thaw cycles under triaxial stress conditions[J].Journal of Henan Polytechnic University(Natural Science) ,2026,45(5):136-144.

三轴应力下液氮冻融煤体力学特征分析

秦雷1,2, 刘鹏飞1,2, 李树刚1,2, 王辉1,2, 母淼1,2, 林海飞1,2

1.西安科技大学 安全科学与工程学院，陕西 西安  710054；2.西安科技大学 西部矿井开发及灾害防治教育部重点实验室，陕西 西安  710054

摘要:目的为了探究不同液氮冻融方式对煤体机械性能的影响，开展三轴应力下液氮冻融煤体力学特征研究。 方法以不同液氮冻融方式处理的煤样为研究对象，利用MTS（mechanical testing & simulation）三轴伺服加载系统开展研究。通过分析煤样的轴向应力-应变曲线，得出不同液氮冻融方式对煤体损伤后的力学性能、轴向能量演化和脆性指标影响规律。 结果结果表明：（1）在绝对液氮冻结时间相同的条件下，受液氮低温作用、孔隙水水冰相变和液氮气化膨胀的共同影响，冻结态煤样的轴向抗压强度和弹性模量均大于融化态煤样；液氮循环冻融对煤样的损伤程度大于单次液氮处理。（2）煤样从冻结态到融化态时，煤样闭合应变、闭合应变变化率、抗压强度变化率、弹性模量变化率逐渐减小。（3）在轴向加载过程中，冻结态煤样吸收能量和耗散能量大于融化态煤样的。随着煤样从冻结态转化为融化态，轴向弹性应变能占比下降，耗散能占比上升。（4）不同液氮冻融方式使煤样含水量不同，导致冻结态煤样脆性指标大于融化态煤样的；液氮冻融循环对煤样的损伤程度大于单次液氮作用煤样的。  结论研究成果可为液氮致裂技术在煤层增透领域的工程应用提供理论依据和试验数据支撑。

关键词:绝对冻结时间;液氮冻融;机械性能;能量演化;脆性指标

doi:10.16186/j.cnki.1673-9787.2024010035

基金项目:中国科协青年人才托举工程项目（2022QNRC001）；陕西省青年人才托举计划项目（20220437）；陕西省青年科技新星项目（2022KJXX-59）

收稿日期:2024/01/12

修回日期:2024/05/09

出版日期:2026-07-24

Mechanical behavior of coal subjected to liquid nitrogen freeze-thaw cycles under triaxial stress conditions

Qin Lei1,2, Liu Pengfei1,2, Li Shugang1,2, Wang Hui1,2, Mu Miao1,2, Lin Haifei1,2

1.College of Safety Science and Engineering， Xi’an University of Science and Technology， Xi’an  710054， Shaanxi， China；2.Key Laboratory of Western Mine Exploitation and Hazard Prevention， Ministry of Education， Xi’an University of Science and Technology， Xi’an  710054， Shaanxi， China

Abstract: Objectives This study aims to investigate the effects of different liquid nitrogen （LN₂） freeze–thaw treatments on the mechanical behavior of coal under triaxial stress conditions.  Methods Coal samples subjected to different LN₂ freeze-thaw treatments were tested using a triaxial servo-controlled loading system. The axial stress-strain response was analyzed to investigate the effects of LN₂ freeze-thaw treatments on mechanical properties， axial energy evolution， and pre-peak brittleness index.  Results The results show that： （1） Under the condition of identical absolute liquid nitrogen freezing time， the axial compressive strength and elastic modulus of frozen coal samples are greater than those of thawed coal samples. This is attributed to the combined effects of liquid nitrogen cryogenic action， pore water phase transition， and liquid nitrogen vaporization expansion. Furthermore， the damage degree of coal samples subjected to liquid nitrogen cyclic freeze-thaw is greater than that of single liquid nitrogen treatment. （2） As coal samples transition from frozen to thawed states， the closure strain， its rate of change， the reduction rate of compressive strength， and elastic modulus reduction rate all gradually decrease. （3） During axial loading， energy absorption and dissipation in frozen samples are higher than those in thawed samples. With phase transition， the proportion of elastic strain energy decreases while that of dissipated energy increases. （4） Different LN₂ freeze-thaw treatments lead to variations in water content， resulting in a higher pre-peak brittleness index in frozen samples than in thawed samples.  Conclusions The research findings can provide a theoretical basis and experimental data support for the engineering application of liquid nitrogen fracturing technology in coal seam permeability enhancement.

Key words:absolute freezing duration;LN freeze-thaw cycles;mechanical behavior;energy evolution;brittleness index