我国大部分开采煤层为自燃或易自燃煤层，煤火灾害十分严重，在主要产煤地区分布有大量的大面积煤田火区，威胁着煤炭资源的安全开发与利用。煤体裂隙网络是影响煤火燃烧传热传质过程的重要因素，对揭示煤田火区燃烧蔓延机制具有重要意义。煤体本身含有丰富的裂隙，在火区高温环境下，煤体受到热损伤作用影响，原生裂隙结构不断发育，同时，在热应力作用下，煤体发生热膨胀产生新的裂隙，其力学特性也发生相应变化，并进一步影响煤体裂隙结构发育。本文以烟煤作为研究对象，采用理论分析、实验研究和数值模拟相结合的方法，开展了煤体热损伤裂隙发育及其力学响应特征研究，对阐明地下火区煤体裂隙发育规律，揭示煤火燃烧传热传质过程提供理论支撑。主要研究内容及成果如下：

采用微焦点X射线断层扫描成像系统结合三维可视化及分析软件，研究了热损伤煤体裂隙发育规律。随着温度增大，煤体主裂隙长度先增大后变化很小；微小裂隙随温度升高先增多后减少。从裂隙发育形态来看，常温至150 ℃主裂隙发育变化明显，200 ℃时主裂隙轴向贯通并演变出横向裂纹，200 ℃ ~ 400 ℃的主裂隙发育形态整体变化不明显，整体裂隙发育为网状。

基于单轴压缩实验，研究了热损伤煤体的破坏模式和力学特性。300 ℃以上的主要是由剪切滑移造成Ⅱ型裂隙，300 ℃以下的裂隙类型主要为Ⅰ型拉裂破坏。常温至150 ℃煤体试样轴向应力在达到峰值后下降迅速，煤样断裂面光滑，呈现出脆性破坏特征；与常温至150 ℃相比，200 ℃ ~ 400 ℃煤体试样轴向应力达到峰值应变大应力小，随后渐进性下降，煤样断裂面粗糙，表现出延性破裂特征。热损伤温度和外部荷载越大，弹性模量越低，抗压强度越低，抵抗变形的能力越弱。通过煤体热破坏温度、煤体裂隙发育与损伤变量之间的内在关联，构建热破坏煤体的力学损伤关系式为D_f = 2.098 + 0.250D - 0.273D² -0.416 exp (-exp (- (T -55.251)/ 48.891) - (T -55.251)/ 48.891 + 1)。

利用ABAQUS模拟软件，进行热-力协同作用下煤体裂隙发育过程研究。各温度下起始裂隙均在模拟试件内部，且存在多条裂隙同时发育。温度和外部荷载导致位移场分布不均匀，位移较大处裂隙发育显著；随着外部荷载和温度增加，径向裂隙逐渐闭合，温度升高和外部荷载增大致使裂隙更加发育，破坏也更严重。破坏时，所有温度均存在斜面剪切破坏，常温时破坏更多呈现拉伸破坏，100 ℃和300 ℃时的大剪切面靠近试件外部。

Most of the coal seams mined in China are spontaneous combustion or easy spontaneous combustion coal seams, and the coal fire disaster is very serious. There are a large number of large-area coalfield fire areas distributed in the main coal-producing areas, which threatens the safe development and utilization of coal resources. Coal fracture network is an important factor affecting the heat and mass transfer process of coal fire combustion, which is of great significance to reveal the mechanism of combustion spread in coal fire area. The coal body itself contains abundant cracks. Under the high temperature environment of the fire area, the coal body is affected by thermal damage, and the original crack structure continues to develop. At the same time, under the action of thermal stress, the coal body undergoes thermal expansion to produce new cracks, and its mechanical properties also change accordingly, which further affects the development of coal crack structure. In this paper, bituminous coal is taken as the research object, and the development of thermal damage cracks and their mechanical response characteristics are studied by combining theoretical analysis, experimental research and numerical simulation. It provides theoretical support for elucidating the development law of coal cracks in underground fire areas and revealing the heat and mass transfer process of coal fire combustion. The main research contents and results are as follows:

The microfocus X-ray tomography imaging system and 3D visualization and analysis software were used in conjunction to study the fracture development law of thermally damaged coal. As the temperature increases, the length of the main fracture of the coal body increases first and then changes little. At the same time, the micro-cracks increase first and then decrease with the increase of temperature. From the perspective of fracture development morphology, the main fracture development changes obviously from room temperature to 150 °C. At 200 °C, the main fracture penetrates axially and develops transverse cracks. The overall change of the main fracture development morphology at 200 °C ~ 400 °C is not obvious, and the overall fracture development is reticular.

Based on uniaxial compression experiments, the failure modes and mechanical properties of thermally damaged coal were studied. Above 300 °C, the type II fracture is mainly caused by shear slip, and below 300 °C, the type I fracture is mainly type I tensile fracture. The axial stress of coal samples from room temperature to 150 °C decreases rapidly after reaching the peak value, and the fracture surface of coal samples is smooth, showing brittle failure characteristics. Compared with the normal temperature to 150 °C, the axial stress of the coal sample at 200 °C ~ 400 °C reaches the peak strain and the stress is small, and then gradually decreases. The fracture surface of the coal sample is rough, showing ductile fracture characteristics. The greater the thermal damage temperature and external load, the lower the elastic modulus, the lower the compressive strength, and the weaker the ability to resist deformation. Through the internal relationship between the thermal failure temperature of coal body, the fracture development of coal body and the damage variable, the mechanical damage relationship of thermal failure coal body is constructed as D_f = 2.098 + 0.250D - 0.273D² - 0.416 exp (-exp (-(T-55.251)/ 48.891) - (T-55.251) / 48.891 + 1).

Using ABAQUS simulation software, the development process of coal fracture under thermal-mechanical synergy was studied. The initial cracks at each temperature are all inside the simulated specimen, and there are multiple cracks developing at the same time. The temperature and external load lead to the uneven distribution of the displacement field, and the fracture development at the larger displacement is significant. With the increase of external load and temperature, the radial cracks gradually close. The increase of temperature and external load makes the cracks more developed and the damage more serious. During the failure, there is inclined shear failure at all temperatures, and the failure at room temperature is more tensile failure, and the large shear surface at 100 °C and 300 °C is close to the outside of the specimen.