Fractal Analysis of Fragmentation Distribution of Rockbursts Induced by Low-Frequency Seismic Disturbances

Lihua Hu,Zhenghu Zhang,Chunan Tang,Xin Liang,Pingye Guo

doi:10.1155/2021/6679891

Abstract

Low-frequency seismic disturbances frequently induce violent rockburst hazards, seriously threatening the safety of deep excavation and mining engineering. To investigate the characteristics and mechanisms of rockbursts induced by seismic disturbances, in this study a series of true triaxial experiments, including the moderate seismically induced, the weak seismically induced, and the self-initiated rockburst experiments under different conditions were conducted. The fractal geometry theory was applied to study rockbursts and the fractal dimensions of fragmentation distribution of different types of rockbursts were calculated. The results show that the fragmentation distributions of both the seismically induced and self-initiated rockbursts exhibit fractal behaviors. For the moderate seismically induced rockbursts, as the static stresses (i.e., the maximum and minimum static stresses) and disturbance amplitude increase, the fractal dimension increases, whereas, as the disturbance frequency increases, the fractal dimension decreases first and then increases. Under similar static loading conditions, the moderate seismically induced rockbursts have the largest fractal dimension, followed by the self-initiated rockbursts, and the weak seismically induced rockbursts have the smallest fractal dimension. There is a linear relationship between the average fractal dimension and kinetic energy of these rockbursts, implying that the fractal dimension can serve as an indicator for estimating rockburst intensity. Furthermore, from a fractal point of view, the energy input, dissipation, and release of these rockbursts are all linear processes.

Highlights

In recent decades, with the worldwide expansion of mining and civil engineering to the deep ground, many large deep-buried tunnels/openings have been built [1]
True Triaxial Experiments of the Seismically Induced Rockbursts. e true triaxial rockburst testing system developed at Guangxi University, China [9, 27, 28], is used to conduct rockburst experiments (Figure 1). e rockburst testing system consists of a true triaxial testing machine, a high-speed camera system, an acoustic emission (AE) system, a control system, and a data acquisition system. e testing machine is an integral frame type press machine, which can independently load and unload in three mutually perpendicular directions, and conventional rock mechanics tests, such as uniaxial/triaxial compression, tensile, and shear tests can be performed with this testing machine
It can be seen that the fractal dimension increases with the increase of σz. is means that, under the preset high static stress, increasing the maximum static stress σz can effectively improve the utilization of the energy input by the cyclic disturbance, so that the rock consumes more energy during the failure process, leading to a higher fragmentation degree

Summary

Introduction

With the worldwide expansion of mining and civil engineering to the deep ground, many large deep-buried tunnels/openings have been built [1]. Under the combined effects of high static stress and dynamic disturbances, violent rockburst disasters are frequently encountered [2,3,4,5,6,7,8,9,10,11]. E dynamic disturbances causing rockbursts can be high strain rate shock waves from blasting [7] or lowfrequency seismic waves/disturbances (or analogous stress waves [2,3,4,5,6, 8, 9]). Ere are many sources of the seismic disturbances in deep engineering, such as natural seismic events, stress waves attenuated from remote blasting, seismic events caused by fault-slip, rockbursts in nearby excavation, and ground vibration caused by huge vehicles [6, 8,9,10]. Due to the high complexity of the seismically induced rockbursts, the driving mechanisms are still not clear and effective control of them is a challenge

Methods

Results

Discussion

Conclusion