循环冷浸致煤样结构损伤的力学性质演化规律

Evolution law of mechanical properties of coal sample structure damage caused by cyclic cold leaching

孔隙、裂隙结构是影响煤体力学性质的重要因素,直接关系到煤层气等能源的安全生产。为了研究在液氮作用下,结构损伤引起煤体力学性质的变化规律,选取辽宁省阜新市新邱煤矿长焰煤作为实验试样,通过循环冷浸的实验方法,采用岩石压缩实验机和声波反馈结构损伤检测实验装置观测不同循环冷浸周期煤样在单轴压缩过程中,孔隙量和单轴抗压强度的耦合变化关系,并建立损伤力学模型,揭示循环冷浸致煤样结构损伤的力学性质演化规律和作用机理。结果表明:(1)煤样的孔隙、裂隙在单轴压缩过程中存在3个阶段:孔隙闭合阶段、孔隙扩展阶段、破坏及其发展阶段,在孔隙闭合阶段时,随着循环冷浸周期的增加,煤样的压缩形变量逐渐增大;(2)通过与未冷浸煤样的应力-应变曲线比较,循环冷浸处理后煤样的单轴抗压强度和脆性程度降低,循环冷浸周期与单轴抗压强度和脆性程度呈负相关;(3)利用ABAQUS软件进行数值模拟,建立煤样冷浸损伤力学模型,发现在液氮冷浸环境下,煤基质收缩,煤的裂隙尖端出现了应力集中现象,当裂隙尖端的应力强度因子超过煤的断裂韧性时,裂隙就会扩展。液氮循环冷浸可以使煤样孔隙、裂隙结构发生损伤变化,促使煤体的力学性质劣化,这将对煤层气抽采和冲击地压防治提供重要的理论参考。

Pore and fracture structure is an important factor affecting the mechanical properties of coal,which is directly related to the safe production of coalbed methane and other energy.In order to study the change law of mechanical properties of coal caused by structural damage under the action of liquid nitrogen,the long flame coal from coal mine of Xinqiu in Fuxin city of Liaoning Province was selected as the experimental sample.Through the experimental method of cyclic cold leaching,the rock compression experimental machine and the acoustic feedback structural damage detection experimental device were used to observe the uniaxial compression process of coal samples with different cyclic cold leaching cycles.Based on the coupling relationship between porosity and uniaxial compressive strength,a damage mechanics model was established to reveal the evolution law of mechanical properties and mechanism of coal structure damage caused by cyclic cold leaching.The results show that(1)there are three stages in the process of uniaxial compression:the stage of pore closure,the stage of pore expansion,and the stage of failure and its development.In the stage of pore closure,the compression deformation of coal sample increases gradually with the increase of cyclic cold leaching period.(2)Compared with the stress-strain curves of coal samples without cold soaking,the uniaxial compressive strength and brittleness of coal samples after cyclic cold soaking decrease,and the cyclic cold soaking period is negatively correlated with the uniaxial compressive strength and brittleness.(3)Using the ABAQUS software for numerical simulation,the mechanical model of coal sample cold immersion damage is established.It is found that under the liquid nitrogen cold immersion environment,the coal matrix shrinks,and the stress concentration phenomenon appears at the crack tip of coal.When the stress intensity factor at the crack tip exceeds the fracture toughness of coal,the crack will expand.Liquid nitrogen cycle cold leaching can damage and change the pore and fracture structure of coal samples,and promote the deterioration of mechanical properties of coal,which will provide an important theoretical reference for coalbed methane extraction and rock burst prevention.