Experimental investigation of rock mineralogical effect on energy transfer and rockbursts induced by tensile fracturing of roof strata

Abstract

The elastic energy released by the tensile fracturing of hard roof strata is partially transferred to surrounding rocks and causes rockbursts during underground coal exploitation. However, the effect of rock mineralogical properties on the transferred energy and rockbursts has not been quantitatively analysed. In this study, three-point bending tests were conducted to reproduce the tensile fracturing of roof strata, with the transferred energy, i.e., the radiated energy as acoustic emission (AE) events and the kinetic energy of fractured rock, being calculated using a calibrated AE system and a digital image correlation (DIC) system. The effects of rock cementation, rock grain size and mineral composition on the energy transfer were quantitatively analysed. The energy transfer during the tensile fracture of roof strata is 2–3 orders of magnitude higher in the siliceous roof strata than in the argillaceous ones. The energy transfer for the siliceous strata stems mainly from the kinetic energy of fractured strata that is one order of magnitude higher than the radiated energy. The high kinetic energy is attributed to a very high crack velocity of 225 m/s. Owing to localized micro-shear failure and the detachment of rock grains, the energy transfer stems mainly from the radiated energy for the argillaceous strata. The energy transfer increases with the increased grain size and brittle minerals. It can be found that rock cementation plays a domain role in the rock mineralogical effects on the energy transfer and rockbursts compared to grain size and mineral component. The tensile fracture of brittle siliceous cemented strata exhibits a much greater rockburst hazard than plastic cemented strata. These findings have implications for the identification of roof strata with rockburst hazards and the effective prevention of rockburst disasters caused by the tensile fracture of hard key roof strata.