Numerical simulation of fracture patterns in roof strata with different thicknesses

Roof breaking is the root cause of rock burst and mine earthquake. However, the classical "thin plate theory" and "thick plate theory" cannot fully reveal the mechanical mechanism of the influence of roof thickness-span ratio on the fracture mode. In this paper, based on the cohesive element technology, the mechanical behavior of cohesive element failure was studied according to the maximum nominal stress criterion and BK fracture criterion, and the fracture mechanical behavior of roofs with different thicknesses fixed on four sides under uniform load was numerically simulated. The fracture pattern and the maximum principal stress evolution laws of roofs with different thicknesses were obtained. The results show that there are three fracture modes of the plates with different thickness: pure tensile fracture mode at the bottom surface, mixed fracture mode around the "X" shape crack, and pure shear fracture mode along the long edge boundary. The crack morphology of thin plate is the transverse "O-X" type, and the crack morphology of thick plate is the "O-❋" type. With the increase of thickness, the tensile-shear mixed failure mode gradually changes from the tensile dominant to the shear dominant.