Experimental investigation into stress-relief characteristics with upward large height and upward mining under hard thick roof

Abstract

According to geological conditions of No. 3 and No. 4 coal seams (namely A3 and B4) of the Pan'er coal mine and the parameters of panels 11223, 11224, and 11124 with fully-mechanical coal mining, we built 2D similar material simulation and FLAC 3D numerical simulation models to investigate the development of mining-induced stress and the extraction effect of pressure-relief gas with large height and upward mining. Based on a comprehensive analysis of experimental data and observations, we obtained the deformation and breakage characteristics of strata overlying the coal seam, the development patterns of the mining-induced stress and fracture, and the size of the stress-relief area. The stressrelief effect was investigated and analyzed in consideration with mining height and three thick hard strata. Because of the group of three hard thick strata located in the main roof and the residual stress of mined panel 11124, the deformation, breakage, mining-induced stress and fracture development, and the stress-relief coefficient were discontinuous and asymmetrical. The breakage angle of the overlying strata, and the compressive and expansive zones of coal deformation were mainly controlled by the number, thickness, and strength of the hard stratum. Compared with the value of breakage angle derived by the traditional empirical method, the experimental value was lower than the traditional results by 3°-4°b elow the hard thick strata group, and by 13°-19°above the hard thick strata group. The amount of gas extracted from floor drainage roadway of B4 over 17 months was variable and the amount of gas per month differed considerably, being much smaller when panel 11223 influenced the area of the three hard thick strata. Generally, the stress-relief zone of No. 4 coal seam was small under the influence of the hard thick strata located in the main roof, which played an important role in delaying the breakage time and increasing the breakage space. In this study we gained understanding of the stress-relief mechanism influenced by the hard thick roof. The research results and engineering practice show that the main roof of the multiple hard thick strata is a critical factor in the design of panel layout and roadways for integrated coal exploitation and gas extraction, provides a theoretical basis for safe and high-efficient mining of coal resources.

Dip Angle Effect on the Main Roof First Fracture and Instability in a Fully‐Mechanized Workface of Steeply Dipping Coal Seams

“…Current studies show that when the tensile stress exceeds the shear stress, while the latter exceeds the compressive stress (σ tensile < σ shear < σ compressive ), the tensile or shear failure is likely to take place in the stratum, and the failure pattern is determined by its tension and shear strengths as well as the stress within the stratum [27,28]. erefore, the analysis of distributions of principal stress and shear stress on the main roof is of great significance.…”

Dip Angle Effect on the Main Roof First Fracture and Instability in a Fully-mechanized Workface of Steeply Dipping Coal Seams

“…When the maximum tensile stress reaches the tensile strength limit at a certain point in the thin rock plate, the tensile fracture occurs, and gradually thin rock plate evolves into spatial surrounding rock structure. Current studies show that when the tensile stress exceeds the shear stress, while the latter exceeds the compressive stress (σtensile < σshear < σcompressive), the tensile or shear failure is likely to take place in stratum, and the failure pattern is determined by its tension and shear strengths as well as the stress within the stratum (Yang et al 2015). Therefore, the analysis of distributions of principal stress and shear stress on the main roof is of great significance.…”

Effect of Advancing Direction of Working Face on Mining Stress Distribution in Deep Coal Mine

“…As the level of modern industry increases year by year, the eastern part of China needs more energy supplies [1][2][3][4][5][6]. e shallow resource was exhausted, and the deep ones begin to develop.…”