The multifractal characteristics of acoustic emission for composite samples subject to simulated field loading condition

Abstract

ABSTRACT The composite strata structure is a common geological formation in western China. The study of the failure characteristics of the composite structure is of great help to the stability evaluation of stope and the prediction of coal mine dynamic disasters. In order to study the influence of different hard rock coefficients on the instability characteristics of composite samples, the triaxial tests with progressive varying confining pressure simulating the field loading condition were conducted on eight groups of composite samples with different hard rock coefficients. The bearing capacity of different samples was tested using the RMT-150B triaxial compression equipment, while the DS-5 type eight-channel acoustic emission monitoring system was employed for simultaneous monitoring of acoustic emission parameters. Additionally, the multifractal theory in mathematics is applied to the analysis of acoustic emission signals, exploring the multifractal characteristics of the time series of acoustic emission signals. The results show that the peak strength of the composite sample decreases first and then increases as the hard rock coefficient increases, which is consistent with the trend of the multifractal spectrum parameter Δ f α of the acoustic emission time series. A significant increase in the low-frequency and high-amplitude signal ratio can be used as a precursor to early indicate the instability in composite samples. The dynamic changes of multifractal parameters at different stages of the progressive varying confining pressure can reflect the influence of axial pressure and confining pressure on the crack propagation in the composite samples, and the two parameters at the hydrostatic pressure stage can be used as a rule-of-thumb for screening the testing samples. Simultaneously, the multifractal parameters can early warn the rock failure much more ahead of time than the conventional approach associated with the warning point obtained in the acoustic emission curves, and its head of time can be reaching 0.015 failure progress.