Discrete element method (DEM) has been widely used in studying fracture development of rock due to its ability to accurately depict particle interactions. In order to more intuitively describe the fracture characteristics of the main roof during coal seam mining using DEM, a novel numerical model for generating irregular particles roof (IPRM) in PFC^3D is developed. In this novel model, irregular blocks are established using rblock, where the balls are placed to form irregular particles. Irregular particles use the flat-joint model, while the smooth-joint model is utilized between these irregular particles. The interlocking effect between the irregular particles of model can well restore the real failure characteristics of the main roof. Using the IPRM, five models of the main roof with varying thicknesses are created to investigate the failure characteristics with different thicknesses under uniform loads. The results show that the load-bearing capacity increases, and deflection decreases with the main roof thickness increasing. Additionally, the increase in main roof thickness leads to a shift in the failure pattern from “o-x” to “o- *,” accompanied by an increase in the fracture angle and the emergence of shear cracks. This change also leads to a transition of failure mode in the main roof from tensile failure to tensile-shear mixed failure. Finally, a mechanical model of the main roof is established, and the influence of different thicknesses and advance distance on the tensile stress and shear stress of the main roof is analyzed. It is found that the increase in the main roof thickness inhibits the development of tensile stress and promotes the development of shear stress, which is also the root cause of shear cracks and shear failure of the thick main roof. The study has theoretical guiding significance for ground control and is conducive to safe production of working face.

离散元法（DEM）由于能够准确描述颗粒相互作用而被广泛应用于研究岩石的裂缝发育。为了使用DEM更直观地描述煤层开采过程中主顶板的破裂特征，开发了一种在PFC ^{3D中生成不规则颗粒顶板（IPRM）的新型数值模型。}在这个新颖的模型中，使用 rblock 建立不规则块，其中放置球以形成不规则颗粒。不规则颗粒采用平接缝模型，不规则颗粒之间采用光滑接缝模型。模型中不规则颗粒之间的互锁效应可以很好地还原主顶板的真实破坏特征。利用IPRM建立了五种不同厚度的主顶板模型，研究均匀荷载下不同厚度的破坏特征。结果表明，随着主顶板厚度的增加，承载力增大，挠度减小。此外，主顶板厚度的增加导致破坏模式从“ox”转变为“o-*”，伴随着断裂角度的增加和剪切裂缝的出现。这一变化还导致主顶板的破坏模式从拉伸破坏转变为拉剪混合破坏。最后建立了主顶板的力学模型，分析了不同厚度和推进距离对主顶板拉应力和剪应力的影响。研究发现，主顶板厚度的增加抑制了拉应力的发展，促进了剪应力的发展，这也是厚主顶板剪切裂缝和剪切破坏的根本原因。该研究对地面控制具有理论指导意义，有利于工作面安全生产。