Unstable Pillar Failure under Soft Loading Condition

AbstractPillar rockburst is an unstable pillar failure and one of the most hazardous problems in the underground mining engineering of deep hard-rock mines. In order to study the mechanism of unstable pillar failure, laboratory tests, numerical simulation, and theoretical analysis are adopted. The disc spring group was used to realize the soft loading function of testing machine, where loading stiffness of testing machine can be adjusted by changing the number and combination mode of disc springs. The results show that the loading stiffness of testing machine has major effect on the post-peak failure behavior of rock specimen, which means that the elastic rebound of disc spring group determines the unstable failure characteristics of rock specimen. The sudden jump Δd of rock specimen deformation and the elastic energy release ΔW of disc spring group all increase with the decreased loading stiffness of testing machine, resulting in more severe rock unstable failure (pillar rockburst). The soft loading condition has buffering and delaying effects on rock failure, but it increases the unstable failure intensity of rock specimen. The numerical simulation reproduced the rock unstable failure and the elastic rebound behavior of disc spring group, which also illustrated the damage evolution process of rock unstable failure. The necessary condition of rock unstable failure and the analytical solution of sudden jump Δd and elastic energy release ΔW were derived based on catastrophe theory, which further verified the experimental results. This study reveals the physical essence of unstable pillar failure, which may help to under the mechanism of pillar rockburst and provide references for underground mining