Abstract
In order to investigate the influence of acid and alkaline environment on dynamic strength and porosity characteristics of bursting liability coal, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis were used to compare the microstructures of coal with different bursting liabilities. A split Hopkinson bar (SHPB) was used to test the dynamic compressive strength and tensile strength of coal samples with different bursting liabilities. The results show that the surface micromorphology and structure characteristics of coal samples with different bursting liabilities are representatives, which can be used as an auxiliary basis to determine the bursting liability of coal seam. The microstructure of coal with strong bursting liability is characterized by mylonitic, fragmentary, and brecciated structure, and the microstructure is diverse and complex. However, the microstructure of no bursting liability coal is single and uniform. Coal with strong bursting liability shows tensile, compressive, and shear cracks produced by tectonic action, and the distribution of cracks is complicated. The development of fissures is greatly affected by the degree of coal metamorphism, organic components, minerals, and other factors. Under acidic and alkaline environments, the decrease amplitude of tensile strength of coal is obviously larger than that in neutral solution, which indicates that under the action of acid-based solution soaking, the easily soluble minerals in coal react with hydrogen ions and hydroxyl ions in solution obviously. Porosity increment in acidic environment is much larger than that in alkaline and neutral environments. The strong bursting liability coal is more sensitive to acidic environment, while the no bursting liability coal is more sensitive to alkaline environment.
Highlights
With the development of the technology of hydraulic fracturing and carbon dioxide gas fracturing to extract coalbed methane, the property transformation of coal reservoir and the scope of mining are expanding [1, 2]
After the rock mass is eroded by the water chemical solution because the water solution takes away part of the cement, the connection between the mineral aggregates is weakened. ere are many microcracks and holes in the rock mass, and the porosity increases, which leads to the deterioration of the strength and other macroproperties of the rock mass. is is a threat to the long-term stability of rock engineering
Based on the X-ray diffraction spectra, the values of the microcrystalline parameters of the tested coal samples can be calculated according to the relevant equations of coal petrology and coal chemistry, and their influence on the bursting liability of coal can be analyzed. e average stacking thickness Lc of the microcrystalline lamellae of the coal sample was chosen as the microcrystalline parameter of the coal, which was calculated as follows: Lc
Summary
With the development of the technology of hydraulic fracturing and carbon dioxide gas fracturing to extract coalbed methane, the property transformation of coal reservoir and the scope of mining are expanding [1, 2]. Due to long-term precipitation and groundwater supplement, the water stored in the underground reservoir of coal mine may cause the change of acid-base property of water, which will weaken the stability of coal pillar dam structure. The change of strength characteristics and porosity of coal under the influence of acid-base environment has not been reported. This topic has an important impact on the efficient extraction of coal seam gas fracturing and underground storage of carbon dioxide and has an important impact on the stability of the underground reservoir coal pillar dam. Chemical kinetics and porosity evolution law are used to explain the degradation mechanism of coal with different bursting liabilities
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