Numerical investigation of coal pillar damage mechanisms for various width-to-height ratios

Pillar stability has garnered significant attention owing to the effects of pillars on coal resource recovery rate, coal pillar stability, and coal bump risk. This study examined the roadway stability control principles of conventional and yield coal pillars. The conventional coal pillars were designed as load-bearing structures with a high load-bearing capacity to carry most of the abutment load, while yield coal pillars were designed as buffer structures for transferring rapidly increasing abutment loads to adjacent solid coal ribs by progressive deformation. In order to analyze the features of dynamical evolution of vertical stress distribution and failure zone during loading, a meticulously validated roof-coal-floor composite mathematical model was established.The energy evolution for coal pillars under diverse w/h ratios was analyzed, and the failure energy ratio and elastic strain energy release rate were introduced to evaluate the failure severity. Furthermore, the behavior and damage mechanism differences between conventional and yield coal pillars were investigated: conventional pillars are designed as strong structures that bear most of the load while the yield pillars are designed to buffer and transfer sudden loads to nearby solid coal ribs by gradually deforming. Finally, two case studies of conventional coal pillars in the Zhulinshan coal mine and the yield coal pillars in the Tashan coal mine were reported.