Experimental and Numerical Investigation on the Role of Energy Transition in Strainbursts

The manifestation of strainbursts is related to the strain energy stored in the rock and how this energy is released and transitioned during unstable dynamic failure. It is of significance to investigate the role of energy evolution and transition during strainbursts and how it is influenced by surrounding rocks. For this purpose, experimental and numerical studies were performed in this study. Composite rock–coal specimens were loaded under the uniaxial compressive condition to produce strainbursts in the laboratory. Numerical simulation was then performed to reproduce the strainburst process observed in the laboratory and investigate the energy-absorbing-transition process associated with the spontaneous instability of the coal in the composite coal–rock specimens. The result has provided direct evidence of the conversion of elastic energy stored within a rock into the forms of kinetic energy to be released during the strainbursts process. For composite rock specimens under unconfined compressive conditions, a softer rock with lower Young’s modulus tends to store more elastic energy than a stronger rock and thus contribute more to the strainbursts that occurred at a surrounding rock. This loading condition is analog to the pillar loading condition in which the pillar is loaded by the roof and floor of the pillar due to the stress distribution resulting from excavation. The kinetic energy of ejected rock in strainbursts is not solely from the elastic energy stored in the zone where the bursts occur but also from the surrounding rocks. Most of the kinetic energy comes from the elastic energy stored within the busting zone and the contribution of the elastic energy stored in surrounding rocks is not significant.