Experimental investigation on occurrence of gassy coal extrusion in coalmine

Coal permeability is a key parameter that affects the drainage of coal bed methane (CBM). Owing to the lower original permeability of coal seams in China, more attention was paid to the study of damage‐induced permeability laws. However, the theory of damage‐induced permeability still needs to be improved. In this paper, the permeability evolution experiments during the complete stress–strain process of coal were carried out firstly. The results are shown that with the increase in axial strain, the coal permeability decreases slowly at first, then increases rapidly, and finally increases slowly or even remains unchanged, and the peak stress point can be regarded as the extreme point of permeability. Then, the equivalent plastic strain was used to describe the damage of coal. Based on the above results, a new damage‐induced permeability model was developed, and the new model can match the experimental data of permeability very well. In addition, solid–gas coupling models of coal were developed based on the new permeability model, and the numerical results show that there is a region of sudden increase in permeability around the borehole where plastic failure occurs, which indicates that the damage‐induced permeability model is reasonable. Finally, the results of numerical simulation of gas predrainage in combination of soft coal and hard coal under different cases were used to optimize the borehole layout of gas predrainage in the field.

Section: Introductionmentioning

confidence: 99%

Damage‐induced permeability model of coal and its application to gas predrainage in combination of soft coal and hard coal

Zhang

et al. 2019

“…18 For instance, during driving roadways and normal mining process, the loading mode on coal body can be simplified as the cyclic loading and unloading process. And in the actual production, the coal seam will encounter the gravity of overlying strata, horizontal in situ stress, and tectonic stress, as well as the dynamic loadings from various mining operations, such as drilling, blasting, roadway heading, and other engineering activities.…”

Section: Introductionmentioning

confidence: 99%

Mechanical response characteristics and permeability evolution of coal samples under cyclic loading

Yang

Cao

Cheng

et al. 2019

Understanding the stress‐cracks‐permeability evolution law inside coal body under cyclic loading is significant to optimize the gas extraction technology and gas disasters prevention technology. In order to explore the influence of mining cyclic stress on the mechanical behavior and permeability variation of gas‐bearing seams, the experiments on permeability evolution, deformation law, and acoustic emission (AE) characteristics of coal samples under cyclic loading with different loading stress level and different loading frequency were carried out. These results indicate that the higher loading stress level, the shorter the fatigue life of coal sample. With the increase of the loading stress level, the change rate of permeability became higher and the relation curves between permeability and loading cycles developed from “U” to “V,” which can be defined and divided into three stages, for example, decrease stage, stable stage, and increase stage. And the permeability in the decrease stage can be modeled as a power function of the loading cycles, while the permeability in the increase stage can be modeled as an exponential function of the loading cycles. Besides, the loading stress level has a significant on the permeability, while the loading frequency has little impact on the permeability evolution. In the process of coal deformation under cyclic loading, the strain development of strain coal samples was in the shape of inverted “S,” while the variation of the peak values of corresponding AE ring counts presented “U” type. In addition, there was a good correlation between the permeability and the AE parameters of coal samples, which provide a new sight into the dynamic variation process of the stress‐cracks‐permeability evolution inside coal body under cyclic loading.

“…[43][44][45][46][47] This precursory information indicates that the AE monitoring can make a good early response to the occurrence of coal and rock dynamic disasters. The AE peak intensity is 2-3 times of that in the stationary period.…”

Section: Relationship Between the Ae Parameters And The Gas Concentmentioning

confidence: 93%

Acoustic emission monitoring technology for coal and gas outburst

et al. 2019

In recent years, with the increase in mining depth and strength, coal‐rock gas dynamic disasters, such as coal and gas outburst, have shown an increasing trend. Acoustic emission (AE) technology has been viewed as a promising method that can effectively forecast coal and gas dynamic disasters. This paper first tests the AE characteristics of coal and rock samples during loading. Then, self‐developed AE continuous monitoring and early warning equipment is used to monitor and predict the coal and gas outburst dynamic disasters on the working face. And it is found that the coal samples primarily show ductile failure, and the AE exhibits the evolutionary characteristics of “rise‐peak‐fall”. The rock samples primarily exhibit brittle failure, and the AE evolution mode is almost no falling stage. Coal and gas outbursts occur after the stress peak. Before coal and gas outbursts occur, there is a clear increasing trend in the AE ahead of the gas concentration variation. When the gas‐bearing coal is damaged by the load, the coal body first breaks due to the stress, and the AE value increases. Then, due to the fracture of the coal body, the crack penetrates, gas rushes out, and the gas concentration increases. The research results can provide an advanced technical method for the monitoring and early warning of coal–rock gas dynamic disasters, and improve the prediction accuracy for dynamic disasters.