Test and study on transfusion law of gas in mining coal

Abstract

In this paper, the seepage tests of mining coal were conducted by servo‐controlled seepage apparatus. These tests consist of conventional triaxial compression seepage tests, and load and unload seepage tests. It was observed that the peak strength and corresponding axial strain of raw coal samples gradually increase with the increase of confining pressure, which conforms to the Mogi‐Coulomb strength criterion, and the internal friction angle was calculated as φ = 42.65°, and the cohesion force was c = 3.56 MPa. The ultimate strength of coal samples after load and unload test was obviously lower than that of the triaxial compression test under the same confining stress conditions, and the deviatoric stress‐permeability curves consistent with the exponential function under two stress paths. In load and unload test, the damage degree of raw coal was characterized by the permeability damage rate and the maximum permeability damage rate. The permeability of coal seam was closely related to the mining stress, it presents a nonlinearly declining as the mining stress increases, and the permeability increases nonlinearly when the mining stress was released.

Experimental Study on Evolution of Fracture Network and Permeability Characteristics of Bituminous Coal Under Repeated Mining Effect

“…Different range values of gray corresponded to specific components: fissure, coal matrix, and mineral from low gray to high gray. The image segmentation, which combined the Gray Average Processing method and the U-Net model in the ORS Dragonfly 4.1, was used to extract and reconstitute different components of coal, as discussed in more detail in our previous study (Zhang et al, 2019). A sampleÕs CT image processing, pre-processing, and 3D reconstitution are illustrated in Figure 9.…”

“…The behavioral changes of coal in the stress field-fracture field-seepage field from the perspective of multi-field coupling were analyzed and provided a theoretical and experimental basis for related research. Zhang et al (2019) studied the evolution of coal permeability under the influence of mining face and found that, under the same confining pressure, the ultimate strength of a coal sample after a loading-unloading test was significantly lower than after the triaxial compression test, while its permeability increased. By simplifying the actual mining stress path, Yin et al (2015) carried out experiments with axial pressure loading and confining pressure unloading of coal samples based on the standard triaxial compression equipment.…”

“…Mahanta et al (2020) implemented the three-stage process to achieve a 3D reconstitute process, which included boundary elimination by gradient computation, pore identification by the threshold algorithm, and minerals identification by the watershed algorithm. Zhang et al (2019) introduced a deep learning algorithm into the threshold segmentation of a digital terrain model to process CT scanning images, significantly improving the model accuracy. Wu et al (2019) developed a permeability prediction model using the fractal dimension-based representative elementary volume (REV) method based on high-resolution CT images.…”

Experimental Study on Gas Seepage Characteristics of Axially Unloaded Coal under Different Confining Pressures and Gas Pressures

“…The results revealed that, in the initial stage of loading and unloading, the permeability of the intact coal body weakens; when the stress difference exceeds the yield strength of the coal sample, the fracture volume increases, resulting in capacity expansion and permeability enhancement of the coal sample. Guo et al [17] found that the cyclic loading and unloading could cause damage to the intact coal body; the permeability of the coal sample is enhanced when the stress exceeds its yield strength; as peak stress rises and damage in the coal sample accumulates, the stress sensitivity of the intact coal body gradually decreases. Cheng et al [18] designed mining stress paths for three stages (loading, unloading and recovery), according to different stress concentration coefficients.…”