The deformation, failure, and filling characteristics of a caving roof in the initial and normal mining stages of a pitching oblique longwall mining area are analyzed using large-scale three-dimensional physical-similitude experiments and numerical calculations to study the characteristics of roof fracture and migration in a steeply dipping seam. The results show that the roof fracture development has evident sequential and spatial characteristics. Among them, immediate roof breaking in different parts of the mining area shows difference in time and space. The failure sequence of the immediate roof in different areas changes with the mining: unique regional stability evolution characteristics are observed in the suspended immediate roof simultaneously, resulting in its significant regional stability on the goaf filling. The unbalanced filling range of the immediate caving roof is smaller than that of the true inclined mining area, and the corresponding compaction filling range is larger than that of the true inclined mining area. The filling process has three stages: filling in the lower-middle parts, followed by the upper and middle parts, and finally the middle parts. The primary breaking formation of the main roof in the mining area is different from the main roof breaking of the general working face with a steep seam. It shows evident asymmetric "O-X" breaking characteristics, and timing characteristics when "X" breaks. The "X" breaking cracks expand in a clockwise direction. The different positions and numbers of the main roof cracks reflect the different failure time sequences of the main roof in different parts of the mining area. In a period caving step distance, the lower part of the inclined middle zone collapses three times; the upper part and the lower part both collapse one time. The location and the migration path of the broken roof are different in different areas, and the broken roof is hinged with the suspended roof in the inclined direction of the main roof caving and filling. The periodic weighting and breaking of the main roof have zoning and timing characteristics. This study provides a scientific basis for the strata control of pitching oblique mining areas in steep seams.
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