Instability and pillar burst mechanism in roof-pillar system with rock beam embedded in elastic foundation

Pillar burst depends not only on the pillar itself but also on other components of the roof-pillar system. Instability theory is applied to optimize the critical condition of pillar instability, thus minimizing the likelihood of a pillar burst event. The instability mechanism and evolution process of a pillar burst for a rock beam embedded in an elastic foundation (EF) are investigated. The unmined orebody (UMO) is considered to be an EF; the pillar’s strain-softening behavior is described by a Weibull distribution. Pillar burst events occur in the post-peak strain-softening stage of the pillar and are mainly dependent on the pillar strength and stiffness ratio rK of the UMO-roof-pillar system. The EF coefficient kf reflecting the UMO property is an important factor affecting rK. The maximum deviation of rK reaches up to 198% when the UMO is regarded as a rigid foundation (RF), which emphasizes the importance of kf in terms of overall system instability. A typical case of partial pillar recovery is simulated to demonstrate that EF hypothesis accurately reflects the UMO response in such a system. The instability conditions obtained by simulation analysis are consistent with the theoretical results. The instability of the UMO-roof-pillar system is the result of many factors, among which the thickness hb and span l of the rock beam are extremely sensitive. The lateral pressure coefficient does not significantly affect pillar instability and can be neglected to some extent. The pillar burst evolution process can be divided into a stability stage, subcritical instability stage, instability stage, and post-instability stage.