Electromagnetic radiation (EMR) energy evolution law of loaded coal-rock and its fracture precursor identification strategy

Abstract

The EMR energy of loaded coal-rock changes with stress, which provides a way for non-contact early warning of coal-rock fracture. Based on the analysis of the energy conversion at the fracture, this paper uses experiment at different rates of 0.3 – 0.5 mm/min to study the evolution law of coal-rock’s EMR energy. Subsequently, a coal-rock fracture precursor identification strategy based on EMR energy characteristic factors is proposed. Finally, its effect and universality are verified. The results show that: the energy conversion due to friction at the coal-rock fracture is the source of the EMR energy, which belongs to the dissipated energy. When coal-rock is loaded, the superposition of EMR energy density is similar to the dissipated energy, both of which show a trend of “slow increase − rapid increase”, which reflects the characteristics of EMR energy more stably and effectively. The variation of the EMR energy of loaded coal-rock has three phases. When approaching fracture, the precursor of EMR energy is 16.6 s earlier than dissipated energy, which fundamentally ensures the early warning effect. The constructed EMR energy characteristic factor EF is related to the damage development rate, whose adjacent maxima can be used to identify fracture precursors of coal-rock. The effect of the proposed two-level identification and early warning strategy for fracture precursors is not affected by the loading rate or the type of coal-rock, and has the “deviation correction” performance, whose average effective early warning duration can reach 33.095 s. These results are beneficial to improving the ability to prevent coal and rock dynamic disasters.