ABSTRACT
After excavation, immediate roof can be simplified as clamped rock beams in trend of the coal seams. Constraints under the rock beams are so deficient that flexures would occur with the self-gravity and even-distributed loadings. However, displacement of immediate and main roofs is uniform. Horizontal shearing failure between immediate roof and main roof is occurred due to obviously variation of constraints, loadings and tangential displacement in Figure 1a, which is prerequisite to bedding separation emerging. Subsidence characterization of both roofs is also conflicting with the stope advancement resulting in occurrence of the bedding separation in Figure 1b. Loading of main roofs as pressure balancing arch would transmit towards terminal of rock beams with remarkable faulted cracks in the main roof. With a larger span of rock beams, tensile cracks in the middle of rock beams and shearing cracks at the end would emerge and finally the first caving of immediate roof happens in Figure 1c.
