Discrete element modeling of progressive failure in a wide coal roadway from water-rich roofs

Progressive failure of roadway roofs is a common failure mechanism in underground coal mines, especially when water-rich roofs are in close proximity to the roadway. In this case study at a Chinese coal mine, the UDEC-Voronoi method was used to investigate the process of progressive roof failure in a wide coal roadway from water-rich roofs. In the numerical scheme, the studied domain was partitioned into polygonal blocks bonded through contacts with pre-defined dimensions. The parameters of polygons and contacts in the Voronoi program were calibrated to rock mass properties obtained through laboratory tests. Based upon laboratory tests and previous research findings, a time-dependent strength degradation process from water absorption was assumed and implemented in the numerical modeling. Next, the progressive failure of a roadway from water-rich roofs was analyzed in detail. The numerical results agreed well with field measurements and observations. This method was demonstrated to reproduce the real phenomenon of roof failure in all of its complexity. The numerical results revealed that the progressive failure mechanism was characterized by an initial fracturing of the roof due to strength degradation, which was followed by significant dilation as fractures grew. The large span of the roadway further contributed to the roof failure process. The results also clearly showed that shear cracks were predominant in the roof and played a major role in the behavior of the roadway roof. Additionally, support and excavation schemes that affect roof stability were observed.