Theoretical description of drawing body shape in an inclined seam with longwall top coal caving mining

Abstract

Understanding the characteristics of drawing body shape is essential for optimization of drawing parameters in longwall top coal caving mining. In this study, both physical experiments and theoretical analysis are employed to investigate these characteristics and derive a theoretical equation for the drawing body shape along the working face in an inclined seam. By analyzing the initial positions of drawn marked particles, the characteristics of the drawing body shape for different seam dip angles are obtained. It is shown that the drawing body of the top coal exhibits a shape-difference and volume-symmetry characteristic, on taking a vertical line through the center of support opening as the axis of symmetry, the shapes of the drawing body on the two sides of this axis are clearly different, but their volumes are equal. By establishing theoretical models of the drawing body in the initial drawing stage and the normal drawing stage, a theoretical equation for the drawing body in an inclined seam is proposed, which can accurately describe the characteristics of the drawing body shape. The shape characteristics and volume symmetry of the drawing body are further analyzed by comparing the results of theoretical calculations and numerical simulations. It is shown that one side of the drawing body is divided into two parts by an inflection point, with the lower part being a variation development area. This variation development area increases gradually with increasing seam dip angle, resulting in an asymmetry of the drawing body shape. However, the volume symmetry coefficient fluctuates around 1 for all values of the seam dip angle variation, and the volumes of the drawing body on the two sides are more or less equal as the variation development volume is more or less equal to the cut volume. Both theoretical calculations and numerical simulations confirm that the drawing body of the top coal exhibits the shape-difference and volume-symmetry characteristic.

Drawing mechanisms for top coal in longwall top coal caving (LTCC): A review of two decades of literature

“…Their frictional coefficients are close to those of actual top coal and gangue in mines. Figure 9 shows typical devices used for top coal drawing tests (Wang et al 2019b, a). A 3D testing device is shown in Fig.…”

“…The dense layout of the marked particles usually leads to a smooth boundary of the TCD. The TCD and TCRR can be calculated according to the location information and mass of the drawn out marked particles (Chen et al 2017;Zhang et al 2018a;Wang et al 2019bWang et al , 2020b. Marked particles are also commonly used in block caving testing (Sharrock 2008;Jin et al 2017).…”

Longwall Top Coal Caving Design for Thick Coal Seam in Very Poor Strength Surrounding Strata

“…Similarly, the use of LTCC for dip angle's seams studied and drawing parameters proposed to improve top coal recovery (Wang et al 2020). The only good side of the very poor surrounding rock strata condition for Alpu lignite field is the high cavability of the roof, which will be helpful for assumed LTCC method.…”

Breaking and mining-induced stress evolution of overlying strata in the working face of a steeply dipping coal seam

“…Producing high-quality coking coal and anthracite yields considerable economic gains (Tu et al 2015;Wu et al 2020). In China, over half of the production of these rare types of coal occurs in steeply dipping coal seams (SDCSs), which make up about 20% of the proven resources (Yun et al 2017;Wang et al 2019Wang et al , 2020. However, SDCS mining safety and efficiency are jeopardized by difficult geological structures and prevailing conditions, the complicated and coupled effects of which require further in-depth investigations (Kulakov 1995;Peng 2006;Wu et al 2014;Das et al 2017;Zuo et al 2020).…”