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Rib spalling is one of the main factors restricting the safe and efficient production of the fully mechanized mining face in gangue-bearing coal seams, and the gangue has significant influence on the occurrence of rib spalling. In this study, the instability process and mechanical mechanism of rib spalling in gangue-bearing coal seams were studied, and the sensitivity of gangue parameters to rib spalling was analyzed. The simulation test of rib spalling under different gangue parameters was carried out by orthogonal tests. The width and depth of rib spalling were taken as evaluation indexes, and the influence of gangue parameters on the rib spalling was analyzed by variance analysis and significance tests. The results show that the failure process of rib spalling is characterized by the fracturing failure of the lower coal body, shear failure of the gangue layer, and the falling off of the upper coal body caused by the gravity; the gangue parameters (thickness, density, joint inclination, and internal friction angle) have an important influence on the sliding instability of the coal wall. In the sensitivity analysis, the influence of gangue parameters on the width of rib spalling is ordered as gangue density > joint inclination > gangue thickness > internal friction angle; the influence of gangue parameters on the depth of rib spalling is ordered as gangue density > joint inclination > internal friction angle > gangue thickness. Besides, the greater the gangue density, the less damage caused by stress concentration, and the lower the risk of rib spalling. [ABSTRACT FROM AUTHOR]

The hyporheic zone is a transition zone for the exchange of matter and energy between surface water and subsurface water. The study of trends and sensitivities of bed hyporheic exchanges to the various influencing factors is of great significance. The surface−groundwater flow process was simulated using a multiphysics computational fluid dynamics (CFD) method and compared to previous flume experiments. Based on that, the single-factor effects of flow velocity (u), water depth (H), dune wave height (h), and bed substrate permeability (κ) on hyporheic exchange in the bed hyporheic zone were investigated. The sensitivity analysis of various factors (H, u, dune wavelength (L), h, bed substrate porosity (θ), κ, and the diffusion coefficient of solute molecules (Dm)) in the surface−subsurface water coupling model was done using orthogonal tests. The results indicated that u, h, and κ were positively related, whereas H was negatively related to hyporheic exchange. H and u showed large effects, whereas κ, Dm, and θ had moderate effects, and L and h showed small effects on hyporheic exchange. This study provides valuable references for the protection and recovery of river ecology.

The hyporheic zone is a transition zone for the exchange of matter and energy between surface water and subsurface water. The study of trends and sensitivities of bed hyporheic exchanges to the various influencing factors is of great significance. The surface−groundwater flow process was simulated using a multiphysics computational fluid dynamics (CFD) method and compared to previous flume experiments. Based on that, the single-factor effects of flow velocity (u), water depth (H), dune wave height (h), and bed substrate permeability (κ) on hyporheic exchange in the bed hyporheic zone were investigated. The sensitivity analysis of various factors (H, u, dune wavelength (L), h, bed substrate porosity (θ), κ, and the diffusion coefficient of solute molecules (Dm)) in the surface−subsurface water coupling model was done using orthogonal tests. The results indicated that u, h, and κ were positively related, whereas H was negatively related to hyporheic exchange. H and u showed large effects, whereas κ, Dm, and θ had moderate effects, and L and h showed small effects on hyporheic exchange. This study provides valuable references for the protection and recovery of river ecology. [ABSTRACT FROM AUTHOR]