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In order to achieving safe and efficient exploitation in horizontal section top-coal mechanized caving of steep and thick seams, pre-blasting of top-coal is one of the prerequisites and analysis of crack evolution law is a key method to achieving good pre-splitting effects. Based on investigations of coal seams and mining conditions, theories of fracture mechanics were applied to explain the process of caving cracks and fracture toughness of coal seams in preblasting caving were calculated. The distribution of caving cracks was determined with in-situ borehole-wall real deformation optical monitoring systems. The results showed that the pre-splitting crack could rapidly develop in the direction of borehole center line and form the failure surface along the same direction in the last; the fracture toughness of B3 and B6 coal seams was 0.5616 and 1.1900 MPa·m 1/2 , respectively. The distribution of caving stress from real monitoring instruments provided a theoretical proof for optimizing the parameters of pre-blasting in top-coal safe mining.

Analysis of Pre-Blasting Cracks in Horizontal Section Top-coal Mechanized Caving of Steep Thick Seams