Abstract
High-pressure air blasting (HPAB) is one type of physical blasting technique that enhances the extraction rate of coalbed methane by impacting the coal mass with high-pressure gas to create cracks within it. First, based on the physical and mechanical parameters of the simulated coal rock mass, the RHT constitutive model of the coal rock mass was established, and its parameters were determined. Then, the laws of crack propagation and stress wave decay in coal induced by high-pressure air blasting were revealed by comparing the effect with that of equivalent explosive blasting. Next, the HPAB experiment was simulated to explore the coal crack propagation law under in-situ stress conditions. Finally, the HPAB experiment was carried out and the results of this experiment were compared with the numerical simulation results. The results indicate that the crack propagation induced by high-pressure air blasting is considered as two major stages, i.e., the crack initiation and crack propagation stage induced by the stress wave and the crack stable propagation stage induced by the duration high-pressure gas. In the case of equal energy, the peak stress wave of high-pressure gas is smaller, decays more slowly and has a longer action time, compared to explosive blasting. Therefore, the number of initial random cracks in coal mass induced by high-pressure air blasting is less, and the range of crack propagation induced by high-pressure air blasting is larger. When λ = 0 (λ is the ratio of the horizontal in-situ stress to the vertical in-situ stress), the in-situ stress in the coal seam can promote the propagation of vertical cracks but inhibit the propagation of horizontal cracks. When λ = 0.5 and 1, the in-situ stress inhibits the propagation of both horizontal and vertical cracks.
Highlights
Coal occupies the dominant position in China’s energy structure, and is expected to occupy about 50% of the primary energy structure by 2050 [1]
Zhu et al [12] investigated the gas drainage and crack propagation of concrete sample under the action of High-pressure air blasting (HPAB) by using COMSOL (Version 3.5, COMSOL, Stockholm, Sweden). Their results show that cracks induced by HPAB can significantly enhance coal seam permeability and gas drainage
The experiment of HPAB coal mass is designed and carried out, and the simulation experiment results are compared with the numerical simulation results for verification
Summary
Coal occupies the dominant position in China’s energy structure, and is expected to occupy about 50% of the primary energy structure by 2050 [1]. Zhu et al [12] investigated the gas drainage and crack propagation of concrete sample under the action of HPAB by using COMSOL (Version 3.5, COMSOL, Stockholm, Sweden) Their results show that cracks induced by HPAB can significantly enhance coal seam permeability and gas drainage. The simulation results obtained using the HJC model cannot describe the tensile damage of the material, and it is necessary to add a failure criterion by the keyword “*MAT_ADD_EROSION” to simulate the crack extension Both the HJC model and the RHT model are the constitutive models used for numerical simulations in LS-DYNA software (Version R7.0.0.1, Ansys, Inc., Canonsburg, PA, United States), and both can be used to characterize the dynamic behavior of materials under blast loading. Final‐ ly, the experiment of HPAB coal mass is designed and carried out, and the simulation experiment results are compared with the numerical simulation results for verification
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