煤体的节理结构是煤层气主要存储空间和渗流通道，而煤层的低渗透性是导致煤层气开采效率低的主要原因，由于节理的角度与贯穿程度不同，使得煤体的物理力学性能产生了较大差异。为了增加煤体的渗透性，利用液氮冷加载煤体的方式对不同种类节理煤样，实验选用阜新盆地长焰煤制成50 mm×50 mm×50 mm的正方体煤样。将煤样放入液氮中浸泡4 h，室温条件下放置20 h，为一个冷加载周期(T)，多周期冷加载直至煤样破裂。运用激光共聚焦显微镜、声波测试仪、单轴压缩试验机等仪器观测煤样的表面、整体裂隙损伤情况和单轴抗压强度的变化程度，揭示不同节理煤样结构在液氮低温冷加载作用下的损伤规律。研究结果发现:① 贯穿型节理煤样(Ⅰpb15°,Ⅰam45°和Ⅰal60°)分别在8T，6T和7T冷加载后，煤样节理结构累积损伤达到煤岩强度极限，发生破碎;② 在相同冷加载周期条件下，贯穿型节理较半贯穿型与未贯穿型节理扩展速度快。③ 煤样冷加载后，与层理呈45°的节理扩展明显。冷加载及作用周期都是煤样节理结构损伤的重要因素，实验结果符合断裂力学理论，并将对煤体结构损伤的进一步研究起到借鉴意义

The joint structure of coal body is the main storage space and seepage channel of coal bed methane,and the low permeability of coal seam is the main reason for the low efficiency of coal bed methane extraction.Because of the different angles of joints and the degree of penetration,the physical and mechanical properties of coal body are quite different.In order to increase the permeability of coal body,different kinds of jointed coal samples were prepared by a cold loading of coal body with liquid nitrogen.The long flame coal of Fuxin basin was used to produce 50 mm×50 mm×50 mm square coal samples.The coal samples were immersed in liquid nitrogen for 4 h and placed at room temperature for 20 h,which is a cold loading cycle (T).With multiple cycles of cold loading,the coal samples were ruptured.Using laser confocal microscope,acoustic wave tester,uniaxial compression tester and other instruments to observe the surface of coal samples,the overall fracture damage and the change degree of uniaxial compressive strength,it revealed the damage law of different jointed coal sample structures under the cold loading of liquid nitrogen at low temperature.The results show that:① The joint structure of coal samples (Ipb15°,Iam45° and Ial60°) has accumulated damage to reach the strength limit of coal and rock after 8T,6T and 7T cold loading,respectively;② Under the same cold loading period,the penetration joint is faster than the semipenetrating joint and the nonpenetrating joint;③ After the cold loading of coal sample,the joint expansion with bedding 45° is obvious.Cold loading and action period are important factors of joint structure damage of coal samples.The experimental results accord with the theory of fracture mechanics and is useful for the further study of coal structure damage.

1 实验

   1.1 煤样制备

   1.2 实验方法

2 实验结果

   2.1 煤样表面节理形貌

   2.2 煤样整体结构损伤程度测定

   2.3 液氮冷加载后煤样的单轴抗压强度

3 机理

   3.1 温度对煤样结构损伤的影响

   3.2 节理角度对煤样结构损伤的影响

4 力学模型

5 结论