Experimental investigation into influence of surrounding rock on strainburst: Insight from failure process and energy partition

The strainburst is the most common type of rockbursts, which may cause injury and death to workers, ruin to underground engineering facilities and destruction to mining/civil infrastructures. However, it is still unknown how the energy released from the surrounding rock affects the strainburst. To explore the effect of the surrounding rock on the strainburst, uniaxial compression tests were carried out on coal-rock combinations to mimic strainburst with the combinations of high-speed camera and strain acquisition instrument. The results demonstrated that the strainburst process can be divided into four stages, i.e., the ejection of small coal fragments, the coal spalling, the transverse volume expansion of local failure area and the violent coal burst. Additionally, two strainburst modes were observed, i.e. tensile strainburst and shear strainburst, relating to the inclination angle of the pre-existent cracks and bedding of the coal blocks. Furthermore, a four-phase model is established for the failure process and energy evolution of the coal-rock combination. It is found that only the released energy in the surrounding rock during the coal burst can affect the strainburst with the energy transfer from the rock block to the coal block. During the coal burst, the post-peak modulus of the coal block grows with the increase in the energy released from the upper rock block. This relationship is accurately fitted by an exponential function, demonstrating a high determination coefficient of 93.5%. As a result, the energy partition of the coal block is modified at the post-peak stage, meaning more released energy in the coal block is converted into the kinetic energy of coal fragments. The findings in this study could promote a better cognition of the intrinsic process and energy evolution for the influence of surrounding rock on strainburst.