Multivariate early warning method for rockbursts based on comprehensive microseismic and electromagnetic radiation monitoring

The phenomenon of rockbursts is notable during the initial stage of the construction of a pumped storage power station in Heilongjiang Province, and thus it is urgent to study the monitoring and early warning of the induced rockbursts along with the deep excavation of the underground powerhouse. The microseismic (MS) and electromagnetic radiation (EMR) monitoring systems are firstly used to identify and analyze the precursory information of the induced rockbursts in the underground caverns of the hydropower station. Meanwhile, a multivariate early warning method is also proposed based on the five quantitative early warning parameters, cumulative energy of microseismic events, apparent stress gradient, cumulative apparent volume rate, variation rate of electromagnetic radiation intensity and variation rate of pulse number. Then the multivariate early warning method is applied in the key area of the underground powerhouse for the potential rockbursts. The comprehensive monitoring results show that there is an increasing trend of the cumulative energy of microseismic events in the early stage of rockbursts while the apparent stress decreases and the cumulative apparent volume increases sharply. In addition, the intensity of electromagnetic radiation and the number of pulses are characterized by large fluctuations, and the precursory characteristics of the surrounding rockmass damage are significant. The application results show that the early warning time and the delineated location of microfracture activity are both consistent with the engineering practice. The proposed method is proved to be effective and may provide new ideas for the early warning of the rockbursts induced in the similar projects.