This study considered the mining roadway with coal pillar protection in the fully mechanized caving face of the Dananhu No.1 Coal Mine, China. Theoretical analysis, numerical simulation, and field tests were conducted, and the stress environment, deformation, and failure characteristics of the mining roadway in the fully mechanized caving face were analyzed. The results revealed that the intrinsic cause for the large asymmetrical floor deformation in the mining roadway is the asymmetrical phenomenon of the surrounding rock's stress environment, caused by mining. This also results in the non-uniform distribution of the mining roadway floor's plastic zone. The degree of asymmetrical floor heave is internally related to the thickness of the caving coal. When the thickness of the caving coal was in the range of 5.9 m, the deformation of the asymmetrical floor heave, caused by the plastic failure in the floor, became more obvious as certain parameters increased. As the rotation angle of the principal stress direction increased, the maximum plastic failure depth position of the floor gradually moved toward the middle of the roadway. This caused a different distribution for the maximum deformation position. The control of the floor heave deformation was poor, and it was not feasible to use high-strength support under the existing engineering conditions. Hence, the control should mainly be applied to the floor heave deformation. When the thickness of the caving coal was more than 5.9 m, the main roof strata was prone to instability and being cut along the edge of the coal pillar; the rock stress environment surrounding the roadway tended to revert back to the initial geostress state. The proposed floor heave control strategy achieved good results, and as the deformation of the floor heave decreased, the workload of the floor heave was also greatly reduced.Energies 2019, 12, 3009 2 of 21 and law governing the asymmetric floor heave of the mining roadway in a fully mechanized caving face, we propose a targeted response plan to ensure the normal operation and safety of the roadway.The floor heave control of mining roadways has always been an important issue in the field of mine pressure and rock mechanics. In recent years, many studies have been conducted to clarify the deformation mechanism of the roadway floor heave, and countermeasures have been proposed to control it. To date, different types of roadway floor heave management methods have been proposed. Hou et al. [8][9][10] reported that the main factor influencing the floor heave of the mining roadway is the front abutment pressure of the coal face. The floor heave of the mining roadway is mainly caused by the post-peak deformation of the floor's broken strata. The deformation of the roof and two sides of the roadway also exert a significant influence on the floor heave. Reinforcing the two sides of the roadway and the corners can achieve better control over the floor heave of the mining roadway. He et al. [11][12][13] proposed a new method to effectively control the ...
Grouting is an important method to reinforce soft coal roadway, and the presence of primary cracks in the coal body has an important influence on the grouting effect. With the discrete element simulation method, the grouting process of the soft coal seam was simulated. The mechanism of primary cracks on grouting was revealed, while the influence of fracture characteristics and grouting pressure on the grouting effect was analyzed. The results demonstrated that grouting in the soft coal seam involves the stages of seepage, rapid splitting, slow splitting, and stability. Due to the presence of primary cracks, the grouting diffusion radius increased significantly. Under the slurry pressure, the tensile stress concentration was formed at the crack tip, and the slurry split the coal once the splitting pressure was reached. In addition, the distribution characteristics of fractures are found to have a great influence on the grouting effect. It is observed that smaller fracture spacing is associated with a larger slurry diffusion radius and thus easier penetration of the primary crack tips. The fracture angle affects the direction of fracture propagation. The secondary fracture formed by splitting is a tensile fracture, which is more likely to extend along the direction parallel to the maximum principal stress. Overall, these simulation results have guiding significance for the setting of reasonable spacing of grouting holes in the practice of grouting engineering.
Due to the influence of deep high stress, geothermal heat, and other factors, the law of desorption of methane in coal seams is more complicated in the process of mining deep coal seams, which is prone to methane over-limit, coal and gas outburst, and other accidents. In order to study the desorption characteristics of coalbed methane under different loading and temperature conditions, the desorption tests at different deformation stages of coal containing methane were carried out in the process of loading-adsorption-desorption-reloading until the coal sample was destroyed by using the seepage-adsorption-desorption test system on coal and rock mass, and the test programs were different combinations of gas pressure 1.2 MPa, two kinds of confining pressure, and three kinds of temperature. The results show that the cumulative methane desorption amount corresponding to each deformation stage presents a convex parabolic increase trend with the increase in desorption time, while the desorption rate presents a power function decay trend. Under the condition of the same desorption time, the cumulative methane desorption amount from large to small is residual deformation stage, compaction stage, near the peak stress, plastic deformation stage, and elastic deformation stage. Under the same confining pressure, temperature, and methane pressure, the maximum desorption rate from large to small is residual deformation stage, near the peak stress, plastic deformation stage, compaction stage, and elastic deformation stage. The desorption and diffusion of methane are promoted under the higher temperature and lower confining pressure, which presents a certain mechanism of promoting desorption. The thermal movement of methane molecules is intensified with the increase in temperature, and the adsorption effect between methane molecules and the molecules at the surface of the coal is weakened. The cumulative methane desorption amount and the maximum desorption rate increase with the increase in temperature. The cumulative methane desorption in the residual deformation stage is obviously greater than that in other deformation stages. The increase in confining pressure inhibits the development and expansion of pore fractures in raw coal specimen and hinders the increase in the effective desorption surface area. The cumulative methane desorption amount and the maximum desorption rate decrease with the increase in confining pressure.
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