Abstract
The artificial-caved rock composited backfilling approach can effectively restrain the dynamic phenomena in the coal seam and the associated roof and floor during mining operations, and can also improve the stability of the system of support and surrounding rock. In this study, based on the analysis of influencing factors affecting the surrounding rock movement and deformation of the composited backfilling longwall face in a steeply dipping coal seam, the roof mechanical model is developed, and the deflection differential equation is derived, to obtain the roof damage structure and the location of the roof fracture for the area without backfilling. The migration law of the roof under different inclination angles, mining depths, working face lengths, and backfilling ratios are analyzed. Finally, mine pressure is detected in the tested working face. Results show that the roof deflection, bending moment, and rotation drop with the increase of the inclination angle and backfilling ratio, whereas these parameters increase with greater mining depth and working face length. The roof failure location moves toward the upper area of the working face as the inclination angle and working face length increases, while it moves toward the center of the non-backfilling area with greater mining depth and backfilling ratio. Results from the proposed mechanical model agree well with the field test results, demonstrating the validity of the model, which can provide theoretical basis for a safe and efficient mining operation in steeply dipping coal seams.
Highlights
The backfilling technique can better control the overburden movement and surface subsidence with increased coal production, it can reduce waste production and restrain the dynamic phenomena on coal seams and the associated roof and floor [1,2,3]
Dipping coal seams (SDCS) have been widely recognized to be difficult to mine [15]. This part of coal seams make up 20% of the proven reserves and 10% of the total coal production in China; 50% of Steeply dipping coal seams (SDCS) are premium coking coal or anthracite coal, which are considered as rare coals and are being mined protectively [16,17]
Since the SDCS can well meet the requirement for self-sliding of waste rock, and considering that the caved roof approaches the goaf bottom and the swelling of the loose rock [16,20,21], the composited backfilling approach, which combines both the artificial waste rock and caved roof waste, can be used in this case
Summary
The backfilling technique can better control the overburden movement and surface subsidence with increased coal production, it can reduce waste production and restrain the dynamic phenomena on coal seams and the associated roof and floor [1,2,3]. The method can significantly reduce the backfilling costs, with a simpler filling system and less backfilling materials, while still enabling the backfilling approach when waste rock is not sufficient for some conditions. This approach can better control the damage in surrounding rock, reduce the strata behavior, and improve the stability of support and surrounding rock, which can be considered as an effective approach to achieve safe and efficient mining of SDCS. This study establishes a mechanical model to account for the roof displacement and deformation in SDCS with the composited backfilling method. The coal seam inclination angle, mining depth, working face length, and backfilling ratio can affect the roof movement, a detailed analysis on each of these factors is given below
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