Coal pillar failure analysis and instability evaluation methods: A short review and prospect

Underground coal mining is characterized by the formation of extensive pillars. Coal pillars serve various purposes, and their instability failure characteristics play a vital role in safety mining. Considerable studies have been conducted over the last few decades on pillar instability and failure analyses. It was concluded that pillar failure for system instability is governed by both the strength of the pillars and the load acting on the pillars. There are several methodologies to evaluate pillar failure for instability; however, each method has its own applicable conditions, and none of them are applicable to all circumstances. This study focuses on methodologies (theoretical models, numerical simulations, and field measurements) for estimating pillar system loads and strengths. In the theoretical model, pillar failure criteria are significant factors for calculating coal pillar strength, and the primary factors for instability evaluation are noted. The general steps of the numerical simulation methods are summarized and analyzed. The finite element method is the most widely used method, whereas the discrete element method has become popular in recent years. Pillar stress, deformation, and fracture development are the main concerns when assessing pillar failure characteristics in field measurements. Finally, we list primary study interests (pillar failure analysis in abandoned and deep coal mines) on coal pillar failure analysis in future studies based on the development of underground coal mining.