Experimental Study of High-Temperature Fracture Propagation in Anthracite and Destruction of Mudstone from Coalfield Using High-Resolution Microfocus X-ray Computed Tomography

Abstract

The coalfield fire is determined by fractures of coal and rock that provide tunnel for gases and heat exchange. To study fracture propagation at high temperatures, high-resolution X-ray computed tomography (CT) was used to scan anthracite and mudstone samples collected from the Qinshui coalfield, Shanxi Province, northern China. The samples were scanned at 100°C intervals as they were subjected to temperatures of up to 500°C. Three-dimensional images were reconstructed by the CT software to analyze changes in the fractures and pores in the samples. The experimental results show that fracturing of anthracite began at 200°C. The generation rate of fractures in the coal samples increases slowly below 300°C, but above 300°C there is a sharp increase in fracture development. This indicates that the thermal fracturing temperature threshold for anthracite is 300°C. During the experiment, it was found that preexisting fractures, voids, and regenerative fractures formed around the hard portions of anthracite particles or along the weak boundaries between particles. Some regenerative fractures developed along the fabric of the relatively crystalline particles within the particle and terminate at the edge of the particle or where the fracture encounters a harder portion of coal. Some fractures even expanded enough to be transformed into voids as temperatures rose. In the mudstone, the porosity changed suddenly at 300°C. This indicated that there was a void generated at 200°C, but the void expanded when the temperature was increased. However, changes in the void were not obvious from 200 to 300°C.

WITHDRAWN: Laboratory Study On Mechanical Response And Failure Mechanism of Red-Bed Soft Rock Under Water-Rock Interaction

“…Furthermore, mudstone strength and slope stability was signi cantly reduced by the drying-wetting cycle (Xu et al, 2018). In recent years, advanced techniques such as SEM and computed tomography (CT) have been used to study microscopic water-induced weakening mechanisms in mudstone, providing a strong basis for researchers to directly observe the mechanical properties of waterweakened rocks (Jiang et al, 2014;Wang et al, 2015;Xiao et al, 2016;Zhang et al, 2012). However, these techniques are not capable of studying the evolution of rock cracks.…”

Review on Applications of X-ray Computed Tomography for Coal Characterization: Recent Progress and Perspectives

“…Porosity evolution pattern of (a) all coal samples, (b) lignite, (c) lean coal, and (d) anthracite at different temperatures. [Panel (a) has been modified with permission from refs − . Copyright 2020, Q. Meng et al Authors under Creative Commons Attribution 4.0 International License (CC BY 4.0).…”

“…Panel (c) has been modified with permission from ref . Copyright 2012, Elsevier, Ltd. Panel (d) has been modified with permission from ref . Copyright 2016, Springer–Verlag, Wien.…”

“…When the temperature reaches 300 °C, the coal matrix starts to rupture, and numerous pores and fractures are generated in the coal, increasing its overall porosity. As the temperature increases, the number of fractures in the coal increases, the fractures become wider, and the overall porosity increases significantly (Figure d) …”

Experimental research on temperature variation and crack development in coalfield fire

“…The crack network, as a key determinant of gas migration, plays a crucial role in the evaluation of coalfield fire [8,9]. It has been reported that the number, width and length of cracks increases with the temperature [10]. Elick et al [11] examined the surface subsidence caused by coalfield fire and the development law of cracks under the high temperature of coal combustion.…”