Abstract
Rock burst is the dynamic failure of rock that poses serious threat to the underground activities. This is particularly the case in deep underground mining in which high in situ stresses and brittle rocks are involved. In this paper, strain burst which a type of rock burst in which gradual accumulation of strain in a rock structure such as a pillar is the cause of dynamic failure is discussed. A steel frame structure was designed as a tool to apply the compressive load to the rock specimen in the lab. The accumulated energy in the beam is high enough to cause sudden rock failure. Rock fragment velocities up to 4 m/s were measured using a high speed camera. A bonded particle-finite element model was used to simulate the rock burst testing in the lab. An approximate formulation is proposed to evaluate the induced kinetic energy due to strain bursting of a pillar. The numerical simulation results appear to support the appropriateness of the proposed formulation.
1. INTRODUCTION
Rock burst is a spontaneous and uncontrolled failure of a brittle rock structure. As a result of rock burst in a pillar, in a very short period of time, the apparently statically deforming rock can turn into the dynamic deformation and violent failure. Consequently, rock particles can be ejected with a velocity of 8 to 50 m/s [1] which can cause fatal injuries and damages to the equipment. Stacey et al. [2] report that during a rock burst, the thickness of the ejected rock can be in the order of 1 meter and hence supports for the rock must be capable of absorbing the rock kinetic energy. One of the first attempts to model rock burst in a room and pillar mining system was proposed by Salamon [3] who used the stiffness matrix (K) of the mining layout together with the slope matrix (A) of the complete load convergence relations of pillars to predict the stability of the rock structure. He showed that the stable situation is achieved if the system matrix K+A is positive definite. Petukhov and Linkov [4] considered the interaction between a linear elastic rock mass with a softening material and used some energy equations to introduce a criterion for the stability of the system. Zubelewicz and Mroz [5] considered rock burst phenomenon as a dynamic instability problem. In their approach, a dynamic perturbation was superimposed into the static solution of the problem and then the possibility of kinetic energy growth of the system as an indication of rock burst was investigated. Lippmann [6] developed an elasto-plastic formulation to simulate the translatory rock bursting in the vicinity of tunnel faces. Whyatt [7] reported on the dynamic failure in deep coal mines. In particular, he showed the growing rate of dynamic failures in mines in Colorado and Utah that have caused injuries or disruption of the mining activities.
