Study on the Stress Field and Crack Propagation of Coal Mass Induced by High-Pressure Air Blasting

Xiao-lin, Yang; Chang, Wang; Chu, Hsin‐Sen; Yan, Shaoyang; Wei, Haixia; Yu, Mengfei

doi:10.3390/min12030300

Cited by 7 publications

(6 citation statements)

References 25 publications

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“…The failure morphologies of HPAB on the specimen are mainly divided into dynamic loading stages under the action of stress wave and the quasi-static loading stages of high-pressure air penetration. , The crack propagation near the blasthole is mainly caused by stress waves. The stress waves decay rapidly with the increase of distance, and the crack propagation in the middle and far regions is mainly caused by stress waves and high-pressure air infiltration and disturbance.…”

Section: Results and Discussionmentioning

confidence: 99%

Experimental Study on the Dynamic Response and Pore Structure Evolution of Coal under High-Pressure Air Blasting

et al. 2022

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High-pressure air blasting (HPAB) is one of the main feasible technologies to improve the extraction efficiency of unconventional gases. At present, there are few visual studies on the evolution characteristics of pore structure in coal under HPAB, resulting in an unclear understanding of the mesoscopic damage evolution mechanism of coal under HPAB. To study the dynamic response and mesoporous structure evolution characteristics of coal under HPAB, simulated coal specimens were used in HPAB experiments. The pore structure characteristics of coal at different locations away from the blasthole after HPAB were analyzed by using computed tomography scanning and 3D reconstruction technology. The maximum sphere algorithm was used to study the law of pore connectivity and reveal the mesoscopic damage evolution mechanism of coal under HPAB. The results indicate that the stress wave and attenuation and the crack propagation direction are greatly affected by the confining pressure. Compared without confining stress, the radial strain attenuation index decreases by 11.97% and the lateral strain attenuation index increases by 15.36% under confining pressure. Without confining pressure, the crack direction is disordered. On the contrary, the crack expands along the σ 1 and σ 2 directions with confining pressure, while the expansion along other directions is inhibited. The stress wave has a great influence on the pore structure in the nearby zone. Compared with before HPAB, at 25 mm distance from the blasthole, the number of pores increased by 24.80%, the number of throats increased by 12.96 times, the maximum equivalent radius of throats increased by 52.15%, and the maximum channel length of the throat increased by 56.06%. With the increase of the distance, the stress wave has little influence on the pore structure in the middle and far zones. The porosity of representative elementary volume and the distance from the blasthole decay in a power function trend. The maximum disturbance distance under HPAB can reach nearly 110 times of the blasthole radius. The study results provide a theoretical basis for enhancing the coal seam permeability and gas drainage of low-permeability coal seam by HPAB.

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Section: Results and Discussionmentioning

confidence: 99%

Experimental Study on the Dynamic Response and Pore Structure Evolution of Coal under High-Pressure Air Blasting

et al. 2022

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“…In addition, the RHT model has not been widely employed in LS-DYNA [98]. To apply the RHT model in LS-DYNA to simulate the damage evolution processes of coal and rock, the mechanical parameters must be determined based on existing mechanical tests [99][100][101]. For some parameters that cannot be established temporarily, we refer to the default values in relevant manuals [102].…”

Section: Numerical Simulation Of Coal and Rock Impact Failurementioning

confidence: 99%

Dynamic characteristics and crack evolution laws of coal and rock under split Hopkinson pressure bar impact loading

Sun

Jin

et al. 2023

Meas. Sci. Technol.

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The aims of this paper are to comprehensively explore both the dynamic mechanical properties and crack evolution characteristics of coal and rock during impact failure. First, experimental specimens are prepared from coal seam, direct roof rock strata and direct floor rock strata in the same area to highlight the correlations between test pieces. Second, a dynamic strain gauge and high-speed (HS) camera are adopted to reflect the stress wave signal and crack evolution. Then, based on digital image correlation (DIC) technology and the mass screening method, the evolution laws of surface cracks during crushing and the distribution characteristics of sample fragments after crushing are studied from the perspective of fractal, and finally compared with those of the simulation analysis. The results are as follows. (1) The coal and rock samples from the same area have both consistency and differences. The dynamic mechanical properties of coal and rock are affected by the impact velocity and the physical properties of the specimen. Higher impact speeds and densities lead to the more obvious brittleness of the specimen when destroyed. Conversely, the sample shows more plasticity and ductile yield. (2) The self-similarity is significantly manifested in the evolution of surface cracks during impact and the distribution characteristics of fragments after impact. The box dimension and quality screening dimension are applicable to quantitatively characterize the evolution process and results of coal and rock fractures. (3) The simulation results based on the Holmquist–Johnson–Cook (HJC) and Riedel–Hiermaier–Thoma (RHT) constitutive models agree well with the experimental results, and the RHT constitutive model is more consistent. This study may contribute to a more comprehensive understanding of the dynamic characteristics and crack evolution laws of coal and rock under impact loading and provide references for further research and discussion.

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“…Coal is formed as a result of a long-lasting chemical reaction and deposition, so it is a tiny heterogeneous body with numerous micro-voids, micro-cracks, etc. [23,24]. If the test was carried out with raw coal, which needed to go through three stages, covering collection, transportation, and processing into a standard shape.…”

Section: Experimental Protocolmentioning

confidence: 99%

Mechanism of Nozzle Position Affecting Coalbed Methane Mining in High-Pressure Air Blasting

et al. 2023

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The use of clean energy is an important part of promoting sustainable energy development. As a clean energy source, coalbed methane, during the mining process, the position of the nozzle can influence coalbed methane extraction efficiency by affecting the cracking effect of coal. To investigate the impact of nozzles on the effect of coal fracture, a test of simulated coal by high-pressure air blasting was executed using nozzles 100 mm, 200 mm, and 250 mm from the orifice. Based on the test results and theories of fracture damage mechanics, two damage fracture models were established for the nozzles located in the middle-upper and middle-lower of the blasthole, respectively. The fracturing process and increased permeability mechanism of the coal were revealed by these two models. The results show that: when the nozzle is 100 mm from the orifice, the high-pressure air impacts the blasthole wall first, similar to a uniform expansion. Multiple longitudinal cracks are formed penetrating the coal. The permeability of the coal seam is greatly improved. When the nozzle is 200 mm and 250 mm from the orifice, the high-pressure air first impacts the bottom of the blasthole. The bottom hole angle and apex hole angle first form horizontal cracks while longitudinal cracks only appear at the same depth as the blasthole. The nozzle is 250 mm from the orifice to form a compaction zone at the bottom of the blasthole. The crack density is small and the tangential depth is shallow, which is not conducive to coalbed methane mining. The results of the research offer a theoretical framework and point of reference for the use of high-pressure air blasting technology in the extraction of coalbed methane (CBM).

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Study on the Stress Field and Crack Propagation of Coal Mass Induced by High-Pressure Air Blasting

Cited by 7 publications

References 25 publications

Experimental Study on the Dynamic Response and Pore Structure Evolution of Coal under High-Pressure Air Blasting

Experimental Study on the Dynamic Response and Pore Structure Evolution of Coal under High-Pressure Air Blasting

Dynamic characteristics and crack evolution laws of coal and rock under split Hopkinson pressure bar impact loading

Mechanism of Nozzle Position Affecting Coalbed Methane Mining in High-Pressure Air Blasting

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