WEBMar 7, 2021 · In coal mining activities, the abutment stress of the coal has to undergo cyclic loading and unloading, affecting the strength and seepage characteristics of coal; additionally, it can cause ...
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WEBSep 1, 2017 · From the perspective of mechanics, coal mining is a loading and unloading process. The typical underground loading and unloading features are mainly distributed on the front side and the protective layer. These loions are often in a complex stress environment. The main variation of the force is shown in Fig. 1. It shows that the force ...
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WEBFeb 20, 2020 · Loading and Unloading Elastic Modulus. Coal is a porous medium that is affected by the geologic environment during the formation process. Coal contains a large number of primary pores and microcracks, resulting in coal being a .
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WEBJun 1, 2015 · Fig. 3 (a) compares the deviatoric stress–strain complete process in coal I under both constant and unloading confining pressures. Fig. 3 (b) plots the complete process of coal II under only unloading confining pressure. Firstly, the deviatoric stress–strain complete process is observed to be almost identical before the loading .
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WEBOct 15, 2022 · Under the stress loading condition, the coal matrix and fractures of PUC samples were compressed simultaneously, and the permeability was regulated by the porefissure structures in the coal matrix. ... Research on the permeability response characteristics of the stress loadingunloading process can provide some clarifiions .
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WEBJul 11, 2022 · The change of elastic modulus of coal samples with the moisture. content of % is the largest in the first and sixth cyclic loading–unloading, decreasing. Mpa and Mpa ...
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WEBAug 1, 2022 · In the cyclic loading and unloading process, the load ing and unloading elastic modulus of coal samples experi ences a rapid increase at the beginning stage of the cyclic
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WEBSep 1, 2020 · The energy evolution and fragment distribution characteristics of different types of rocks were investigated through the uniaxial cyclic loading and unloading experiments for granite, redsandstone, coal, gypsum, and highwater material. Based on the results of the study, the following conclusions are drawn.
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WEBApr 5, 2021 · For example, in the loading and unloading process, much elastic energy accumulates in the coal and rock mass with increasing elastic deformation. Under unloading, elastic energy is released. In the test process, the total energy density and elastic energy density of the coal mass can be expressed as Formulas ( 2 ) and ( 3 ).
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WEBJan 23, 2021 · On the premise that the point of the maximum abutment pressure is the demarion point of gas migration, an experimental research was conducted on gasbearing coal by using a thermofluid–solid coupling test system. The research results demonstrate that irreversible strain and elastic modulus increase with increase in .
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WEBFeb 27, 2023 · The damage and fracture of coal is accompanied by a complex energy conversion process, and these different stages of energy evolution are closely related to coal failure. In this paper, an evolution model describing the behavior of coal failure was proposed using the energy dissipation under cyclic loading/unloading. The energy .
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WEBMay 25, 2019 · To explore the differences in deformation failure and energy evolution and simulate the real excavation conditions of coal masses at different depths during the coalmining process, an unloading failure experiment was conducted. The experiment included coal samples at different depths from the no. 15 coal seam of the Ji group in the .
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WEBOct 10, 2022 · Permeability changes with confining stress loading–unloading: (a) is the PUC; (b) is the aclastic coal; (c) is the mylonitic coal; (d) is the loading–unloading process of confining stress. The increase in confining pressure compressed the coal matrix and internal fissures of the coal cores, and their permeability rapidly and then slowly ...
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WEBDec 15, 2023 · Then, gas seepage tests of the coal rock damage process with different hydrostatic pressure and gas pressure conditions under triaxial stress loading–unloading were carried out. Finally, the model was verified based on the experimental results of this paper and other studied presented in the literature, and the verifiion results were ...
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WEBJan 22, 2024 · Su 21 studied the AE and damage characteristics of coal and rock under cyclic loading. ... There is an energy conversion process for loading and unloading rocks. Based on the principle of energy ...
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WEBDec 12, 2021 · 1. Introduction. With an increase in the coal mining depth, the influence of high insitu stress and high osmotic pressure on the pore structure and the permeability of surrounding rocks of the coal body in working faces has been increasingly investigated. 1 For deep underground engineering, due to the action of severe disturbances such as .
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WEBApr 28, 2017 · During the postpeak loading and unloading process, the flow rate of the coal sample will decrease with the loading of confining pressure but increase with the unloading of confining pressure, and ...
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WEBDec 1, 2020 · Fig. 9 shows that coal rocks with fracture networks of different levels of complexity all undergo essentially the same permeability evolution process under loadingunloading conditions, although differences in the final increase in permeability can be observed. The higher the complexity of the initial fracture structure is, the higher the final ...
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WEBDec 1, 2019 · This loadingunloading process can also occur in roomandpillar mines as the cascading pillar failure occurs. Fig. 1 (c) shows a series of gascontained pillars each subject to the same tributary area loading. If one of the weak pillars fails (Fig. 1 (c1)), the load will transfer to neighboring pillars causing an abrupt pillar loading .
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WEBIn the excavation process, the coal pillar will undergo shear failure due to repeated loading and unloading from mining stress. Meanwhile, plastic flow will occur after shear failure. The permeability change of the coal pillar under plastic flow is closely related to the loading path. Through a permeability test of the coal sample after shear yielding under .
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WEBAug 20, 2022 · The strain of coal mainly occurs in the first loading process. Compaction occurs largely during the loading process, and the fracture closure during this stage is mainly irreversible plastic deformation. The volume and morphology of the sample after unloading cannot be fully restored to the situation at the initial loading stage.
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WEBJun 1, 2020 · In the loadingunloading tests, the PER value was calculated based on the initial porosity and the relative increment in the volumetric strain during the whole loadingunloading process. A lower ...
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WEBJan 1, 2018 · During the process of deep coal mining, coal seams are generally under the true triaxial stress state (σ1>σ2>σ3), which is influenced by the crustal stress and strong excavation disturbance.
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WEBFeb 1, 2019 · the pressure loading and unloading process was explained theoretically based on a tight fourparticle packing unit, whic h provides a reasonable explanation for the experimental results
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WEBAug 1, 2019 · The results showed that the change trend of permeability was negatively correlated with the confining pressure in the process of loading/unloading of coal and it was divided into three stages for ...
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WEBMar 16, 2023 · Research on the mechanical properties and damage evolution of coal during true triaxial cyclic loading and unloading is of great significance for maintaining the longterm safety and stability of underground engineering structures in coal mines. In this paper, firstly, the deformation, strength and fracturing characteristics of coal during true triaxial .
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WEBIn actual mining situations, the advancing speed of the working face is usually accelerated, which may affect the failure and seepage characteristics of gasbearing coal, and may even induce dynamic disasters. In order to discover the effects of such accelerated advancement of the working face, an experimental study on the failure and seepage .
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WEBFeb 1, 2024 · In the process of coal seam mining, the coal is disturbed by periodic pressure. This disturbance can be simplified to the loading process under different stress environments [5], [9], [10], [45], and the characteristics of the mining stress path are different under different advancing speeds [46]. Fig. 3 shows the loading path of the .
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WEBUnloading and loading freight happens so often that workers and management can become complacent to the inherent dangers that exist in the process. Unloading and loading freight is almost always under some sort of time constraint. This issue and tighter supply chain windows can exacerbate the problem and create an even more dangerous .
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WEBFeb 15, 2024 · The overall trend indied a gradual decrease in the fractal dimension of the SPF, suggesting that the SPF within the coal were progressively fractured and permeated as the confining pressure was unloaded, thereby reducing the complexity of the SPF within the coal. (3) The complete process of unloading the confining pressure was simulated .
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