Simulation of Failure Mechanisms around Underground Coal Mine Openings Using Discrete Element Modelling

Roof failure has always been a major concern in underground coal mine roadways. Understanding the failure mechanism of roadway roofs is important for improving the safety of underground coal mines and reducing economic loss. In this research, a numerical modelling methodology named UDEC Trigon in 2D and 3DEC Trigon in 3D and based on a discrete element framework is developed to model rock mass behaviour, with a particular focus on the damage process including generation and propagation of fractures, and heavy dilation in the post-peak failure stage. Simulation of compression and Brazilian tests indicates that the methodology can capture different failure mechanisms under varying loading conditions. The UDEC Trigon is then used to investigate shear failure mechanism in roadway roofs. The results suggest that shear cracking plays a dominant role in the roof shear failure. Rock bolts can aid in ensuring the retention of more rock bridges which is critical to the roof stability. Cutter roof failure, which is a three-dimensional roadway rock failure mechanism, is studied using both PFC3D and 3DEC Trigon. The 3D models explicitly capture the cutter roof failure process and found that incorporating bedding planes and cross joints results in a more distinct cutter failure. Roadway squeezing failure mechanism is studied using the UDEC Trigon approach. The results show that the UDEC Trigon approach is able to reproduce the large dilation due to fracturing of rock mass surrounding a roadway under two distinct situations: high mining-induced stress and strength degradation of moisture sensitive rocks. In addition, the UDEC Trigon approach is used to simulate the progressive caving process of a longwall panel of coal. It is found that compressive shear failure, rather than tensile failure, is the dominant failure mechanism in the strata above the goaf. A further demonstration of the potential of UDEC Trigon in capturing roadway failure is presented as a case study of a roadway driven adjacent to unstable goaf in the Wuyang Coal Mine. The case study reveals that the combination of Synthetic Rock Mass (SRM) and UDEC Trigon is able to evaluate failure mechanisms in underground coal mines.;The insights gained from this research provide an improved understanding of typical failure mechanisms in underground coal mine roadways, guiding the design of panel layout and roadway support. The 3DEC Trigon method provides an alternative for simulating rock damage under real 3D conditions.;Keywords: Numerical modelling; brittle fracture; shear failure; cutter roof; squeezing; longwall mining.