Analytical and numerical investigations on pillar rockbursts induced by triangular blasting waves

Abstract

Rockburst is a term used to describe a sudden and violent failure of rock ranging in magnitude from abrupt ejection of small rock fragments to sudden collapse of a large section of a roof or sidewalls in underground excavation, which could cause damage of equipment, casualty of workers, or even abandonment of tunnels and mines. It is observed that rockburst has often been induced by dynamic loads in terms of triangular stress waves from blasting in the proximity. This paper studies the mechanism of pillar rockburst analytically and numerically, under the excitation of triangular stress waves from underground blasting. The pillar rockburst is regarded as a problem of dynamic instability (or dynamic buckling) of a column. To formulate the problem, a governing equation of motion was developed, which was a second-order differential equation with variable coefficients of Mathieu-Hill type. An analytical method was proposed to investigate the effects of various factors on the mechanism of pillar rockburst, such as the amplitude of static and dynamic component loads, frequency, slope, duration, multimode, peakedness, and time gap between two dynamic loads. A numerical matrix method was then introduced to verify the analytical results. It was found that the amplitude and frequency of dynamic disturbances play a critical role in the occurrence of pillar rockburst in terms of the mechanisms of perturbation effect and parametric resonance. Longer time gap between dynamic component loads will help reduce rockbursts. Meanwhile, the positive slope of triangular loads has the same influence as the negative slope. Based on the mechanism obtained, measures were proposed to alleviate the hazard of rockbursts in underground excavation.