School of Resources and Geosciences, China University of Mining and Technology
Engineering Research Center of Zero-carbon and Negative-carbon Technology in Depth of Mining Areas, Ministry of Education (China University of Mining and Technology)
Geothermal Resources Research Center, China University of Mining and Technology
The Fifth Geological Brigade, Geology and Mineral Resources Bureau of Jiangsu

自燃煤层围岩在不同高温作用下会引起不同程度的结构损伤，导致其物理力学性质和工程地质效应发生显著变化。为深入认识烧变过程中岩石的结构演化规律，以徐州某矿底板灰岩为研究对象，开展不同温度作用下的热破裂试验，从多尺度上探究岩石热破裂的规律，并结合数值模拟和微观结构测试揭示其发育机理。结果显示：(1)方解石填充裂隙、层理等相对软弱结构面的热破裂温度阈值在300~400℃，完整岩石结构的热破裂温度阈值在500℃左右；600℃之前的热破裂形态较简单，基本是直线型裂纹，且宽度较小、数量较少；700℃以上出现宽度和长度显著增大的弧形热裂纹，热裂纹两侧试样的颜色有明显区别，靠近热裂纹的白色部位还发育一些连通弧形裂纹的次级小裂纹；800℃时，试样颜色全部变白，结构完全破碎，成散体状。(2)从微观结构和热应力角度阐释灰岩热破裂发育机理，发现试验温度路径下试样的热破裂主要发育在降温过程中，且最大热应力差主要在靠近试样表面的近似环形带上分布。500℃以下的热破裂成因主要为热应力在试样的原始缺陷处集中，并超过了部分软弱结构的抗拉强度；500℃以上受热应力与矿物分解共同控制，500℃以上升降温过程中的最大热应力基本超过灰岩的抗拉强度，且菱镁矿、白云母、白云石等矿物逐渐分解，逐渐增多的内部缺陷为应力集中提供有利条件，加剧了热破裂的发育；当温度达到800℃时，热破裂发育程度很高，且白云石和方解石快速分解，生成CaO，部分CaO在冷却过程中与空气接触生成Ca(OH)2，热裂纹与主体矿物分解共同导致试样结构的破碎。研究成果可为岩体破裂和地质结构演化分析奠定基础。

Spontaneous combustion of coal seams will cause different degrees of structural damage to surrounding rocks at different high temperatures, significantly altering their physical and mechanical properties and engineering geological effects. To delve into the structural evolution patterns of rocks during burning, this study investigated the limestones from the floor of a coal mine in Xuzhou. It conducted thermal cracking experiments under different temperatures, exploring the thermal cracking patterns of rocks on multiple scales. Furthermore, this study revealed the genetic mechanism of thermal cracking by combining numerical simulations and microstructure tests. Key findings are as follows: (1) The thermal cracking temperature thresholds ranged from 300℃ to 400℃ for relatively weak structural planes like calcite-filled fissures and bedding and around 500℃ for intact rock structures. Below 600℃, rock samples exhibited relatively simple thermal cracking morphologies dominated by a few narrow linear cracks. Above 700℃, arc cracks with significantly increased widths and lengths emerged, displaying distinct colors on both sides. Besides, some secondary cracks connected to the arc cracks were observed in the white parts near the arc cracks. At 800℃, the rock samples all turned white, with structures completely broken and appearing in a dispersed form. (2) This study aimed to account for the genetic mechanism of thermal cracking of limestones from the perspective of microstructure and thermal stress. Findings indicate that the thermal cracking of rock samples primarily occurred as the temperature dropped in the experiments, with the maximum thermal stress differences primarily distributed on the approximately annular zones near the rock sample surfaces. Below 500℃, the thermal cracking was principally because the thermal stress was concentrated in the original defects of rock samples and exceeded the tensile strength of some weak structures. Above 500℃, the thermal cracking was jointly governed by thermal stress and mineral decomposition. In this case, the maximum thermal stress generally exceeded the tensile strength of limestones during temperature fluctuations. Furthermore, as minerals such as magnesite, muscovite, and dolomite gradually decomposed, the gradually increasing internal defects created favorable conditions for stress concentration, exacerbating thermal cracking. As the temperature reached 800℃, rock samples manifested a high degree of thermal cracking. This was accompanied by the rapid decomposition of dolomite and calcite, producing CaO. Part of CaO was exposed to the air during cooling, generating Ca(OH)2. Therefore, thermal cracking and the decomposition of predominant minerals jointly led to the structural fragmentation of rock samples. The results of this study lay the foundation for analyzing the evolutionary mechanisms of rock mass fracture and geological structure.

国家自然科学基金项目(41807233)；江苏省地勘基金项目(苏财资环〔2021〕45号)

张卫强，曹志成，周琦忠，等. 灰岩在烧变过程中的热破裂机制试验研究[J]. 煤田地质与勘探，2024，52(4)：1−10.

ZHANG Weiqiang，CAO Zhicheng，ZHOU Qizhong，et al. Experimental study of the thermal cracking mechanism of limestones during burning[J]. Coal Geology & Exploration，2024，52(4)：1−10.