Mine disasters, such as large deformation, floor heave, and roof fall, occur extremely easily in weakly consolidated soft rock strata in western China, posing enormous challenges to traditional anchorage support design. To avoid tensile failure of bolts as a result of the superposition effect of stress accumulation, a segmentally yieldable anchorage support, taking into consideration the different failure zones in surrounding rock, is presented in this paper. First, load transfer mechanisms and the process of anchorage failure are analyzed for end anchorage, full-length anchorage, and segmentally yieldable anchorage based on numerical pull-out tests. Results show that the load transfer follows a multipeak chain-like trend in the case of multipoint segmental anchorage, and that the peaks of stress attenuate slowly. Therefore, the proposed anchorage type can leverage the shear strength effectively. Furthermore, numerical models for the applications of the aforementioned three different anchoring modes to weakly consolidated soft strata are established. Results indicate that segmentally yieldable anchorage can withstand larger tensile deformation and surrounding rock deformation. Moreover, the bolt shows higher strength reservation. A combination of these characteristics is conducive to controlling deformation and damage during roadway excavation.

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.

No abstract

No abstract

No abstract