Fracture Mechanical Behavior of Cracked Cantilever Roof with Large Cutting Height Mining

Abstract

Accurately predicting the roof collapse span is crucial in ensuring the safe production of thick seam mining with large mining height, which is easy in forming a “cantilever beam” structure. Considering roof damage caused by roadway excavation and coal seam mining disturbance, the fracture mechanics model of large mining height roof cantilever beam with nonpenetrating cracks was established. The roof was divided into two parts: the crack-affected area and the crack-unaffected area. The analytical expression of the boundary between the two areas was established by fracture mechanics methods. Based on the boundary equation, the influences of crack size, crack inclination, roof lithology, and roof thickness on the roof crack-affected area were analyzed in detail. Finally, the accuracy of the theoretical model was verified by numerical experiments using the extended finite element method. The results demonstrate that the size of the area affected by the vertical crack increases with the increase of the crack size and the thickness of the roof. The influence of the crack decreases with the increase of roof lithology. The probability of early periodic collapse of a thin roof with the crack is increased. When the crack is completely located in the interior of the roof, the crack-affected area shrinks greatly with the decrease of the crack inclination. When the crack inclination is small, the crack will not cause the early collapse of the roof. Overall, the conclusions obtained are of great significance for predicting the collapse span of a cantilever roof with initial damage in large mining height.