Mechanism of Dynamic Failure in Roadways with Thick and Competent Roof Strata: A Case Study

Rock and coal dynamic failures have a higher chance to occur when thick and competent roof strata are presented, which can build up a high level of energy. This paper studied the fracturing characteristics of the competent roof strata during longwall face retreat and their effects on roadways’ stability to gain an improved understanding of the rock dynamic failure occurred in roadways as well as the associated ground controls. The results indicated that the main reason of dynamic failure in roadways was the structural change of lateral main roof over a chain pillar, which transformed from the cantilever beam in the period of primary mining impact (PMI) to the triangular arch in the period of secondary mining impact (SMI). Based on corresponding mechanical models developed for the lateral main roof over the chain pillar, it was calculated that the force on roadways’ roof in the period of SMI was 3.7 times larger than that in the period of PMI. Then, the dynamic failure control method of increasing the chain pillar width was proposed. The stress distribution and deformation of roadways with different chain pillar widths were simulated using FLAC3D. The results indicate that as the pillar width increases, the influence of secondary mining on roadways’ stability decreases, and a threshold of not less than 30 m pillar width was suggested. The outcomes of this study would provide guidance for the design of chain pillars where thick and competent roof strata are presented.

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