Spatial Fractal Structure of Microseismic Events for Different Types of Rockburst in Deeply Buried Tunnels

Abstract

Based on a large amount of real-time microseismic monitoring data and hundreds of rockburst cases of different types stemming from the construction of deep tunnels at Jinping Mountain Hydropower Station, Sichuan Province, China, a fractal calculation method, which is suitable for the study of linear tunnels, was proposed to investigate the self-similarity of the spatial distribution of the microseismic events occurring during the development of strain-structure slip rockbursts and strain rockbursts. The range and distribution characteristics of spatial fractal dimensions in the development process of different types of rockbursts were also compared and analyzed. The overburden above the tunnels, which are largely excavated in marble, is between 800 and 2,525 m. The results indicate that the spatial distribution of microseismic events during the evolution of rockbursts displays fractal properties. The daily spatial fractal dimensions of microseismic events decrease during the development of a rockburst, and are reduced to the minimum value as a rockburst occurs. There is an inversely proportional relationship between the daily spatial fractal dimension and microseismic energy release. The spatial fractal dimensions of microseismic events associated with a whole rockburst can be used as a basis for estimating the type of rockburst: spatial fractal dimensions greater than and less than 1.3 correspond to strain rockbursts and strain-structure slip rockbursts, respectively. For different types of rockbursts, if the intensity is higher, the spatial fractal dimension is smaller. The conclusion provides a basis for the development of a warning system for the prediction and prevention of different types of rockbursts in deep tunnels.