Study on fractal characteristics of b value with microseismic activity in deep mining

The deep mine excavation usually induce dynamic disasters of rock mass. Huize Lead & Zinc mine is a 1000 m deep mine in China. In this deep hard-rock mine, the basic characteristics are high in-situ stress, abundant water and fractured surrounding rocks. In light of the complicated geologic conditions of this mine, a digital 24-channel microseismic monitoring system was established to monitor the microseismic events in the deep 8# orebody of this mine. During the monitoring period, the microseismic parameters such as magnitude, the number of microseismic events and the magnitude-frequency relation (b value) were recorded. After analyzing the monitoring data acquired in 4 months, the changes of b value and fractal dimension were determined with time and stopes collapse. Results show that rock failure is closely related with b value. The stress concentration of the local rock mass induces crack compaction, initiation, and extension with the disturbance of mine excavation, but b value shows an increase and is relatively quiet. Once the dynamic disasters are caused by rock failure, b value shows an abrupt decrease. Based on the site examination, the probability of rock failure increases with the decrease of b value; on the contrary, the probability of rock failure decreases. The fractal dimensions also show this property. This conclusion provided a good reference for forecasting of rock mass stability monitoring in site excavation.