Stability Analysis of “Support-Surrounding Rock” System for Fully Mechanized Longwall Mining in Steeply Dipping Coal Seams

Abstract

The key to safe and efficient longwall mining of steeply dipping seams lies in the stability control of the “support-surrounding rock” system. This study analyzes the difficulties encountered when controlling the stability of the support during the longwall mining process of steeply dipping coal seams in terms of the characteristics of the nonuniform filled-in gob using a combination of physical tests, theoretical analyzes, and field measurements. Considering the floor as an elastic foundation, we built a “support-surrounding rock” mechanical model using data obtained on support-surrounding rock systems in different regions and the laws of support motion under different load conditions. Our findings are summarized as follows: first, depending on the angle of the coal seam, the caving gangue rolls (slide) downward along the inclined direction, resulting in the formation of a nonuniform filling zone in the deep gob where the lower, middle, and upper sections are filled, half-filled, and empty, respectively. In addition, an inverted triangular hollow surface is formed on the floor of the gob in the middle and upper sections behind the support. Furthermore, as the angle of the coal seam, length of the working face, and mining height increase, the characteristics of the nonuniform filled-in gob are enhanced. Second, we found that because of the gangue support, the “support-surrounding rock” system is relatively stable in the lower part of the working face; however, in the middle and upper sections of the working face, the contact method and loading characteristics of the support are more complicated, making stability control difficult. Third, the magnitude and direction of the load, action point, and mining height affect the stability of the support to varying degrees, with the tangential load and action position of the roof load having the most significant impacts on the stability of the support. Under loading by the roof, rotation and subsidence of the support inevitably occur, with gradually increasing amplitudes and effects on the intersupport and sliding forces. Finally, we found that overall stability can be achieved by adopting measures involving “sliding advancement of supports” and applying a “down-up” removal order. These research results serve as a significant reference and guidance for longwall mining applications.

Research on the hydraulic support face guard mechanism and coupling characteristic of rib spalling in large mining heights

“…The coal wall stability is directly impacted by the coupling relationship between the face guard mechanism and the coal wall structure 37 , 38 . On the one hand, the face guard mechanism can apply actively support to the rib, avoid spalling coal blocks and gangue from damaging workers and equipment.…”

Experiment on Space-Time Evolution Characteristics of Deformation and Failure of Overlying strata in Longwall Mining of Steeply Dipping Coal Seam

“…Affected by seam angle, there are significant differences in strata behavior, strata migration law and support-surrounding rock relationship between steeply dipping coal seam and horizontal coal seam. Over the past three decades, a large number of scholars have studied from different aspects of longwall fully mechanized mining in steeply dipping medium thick coal seam, longwall fully mechanized caving mining in thick coal seam, and coal seam group mining under different mining methods of strata behavior(e.g., Luo et al, 2021;Sun et al, 2019;Wang et al, 2020;Yang et al, 2021), bearing capacity of gangue(e.g., Ding et al, 2022;Lv et al, 2022;Wei et al, 2021), space-time evolution characteristics of mining transfer paths(e.g., Chi et al, 2020;Luo et al, 2022aLuo et al, , 2022bLuo et al, , 2022c, disaster-causing mechanism of irregular random separation in stope space(e.g., Hu et al, 2020;Wu et al, 2021), surface subsidence(e.g., Huang et al, 2020;Yin et al, 2018), coupling mechanism and stability control of support-surrounding rock system under interaction of roof and floor(e.g., Liu, 2021;Shen et al, 2021;Wang and Jiao, 2016;Wang et al, 2018;Xie et al, 2021), mechanism of support and equipment downturn and surrounding rock disaster(e.g., Luo et al, 2018Luo et al, , 2022aLuo et al, , 2022bLuo et al, , 2022c. The existing research has solved the basic problems of safe and efficient mining of steeply dipping coal seam to a certain extent.…”