Correlational fractal characterisation of stress and acoustic emission during coal and rock failure under multilevel dynamic loading

Abstract

The fractal characterisation of stress and acoustic emission (AE) of coal and rock failure may provide quantitative guidance for analysing the stability of rock mass during excavation engineering. The correlation between stress and AE data was calculated using fractal theory methods and Grassberger-Procaccia (G-P) algorithms to evaluate the damage and degree of flaw in coal and rock materials under multilevel dynamic loading (MDL). First, the mechanical properties of the testing device were developed to obtain synchronous data regarding the stress and AEs of coal and rock specimens under MDL. Second, strength deterioration behaviour and the Felicity effect during coal and rock failure are compared under different levels of dynamic loading. The results show that cumulative dynamic loading are less than the uniaxial compression strength of coal and rock. The Felicity effect is notable, and Felicity ratios decrease to 1 with increased loading velocity. Finally, stresses and AE signals are considered as the data mining specimens of correlation dimensions based on the G-P algorithm. Fractal characteristics on stress and AE coupling properties become more notable as the correlated dimensions become larger. However, the Felicity effect is less prominent, reflecting a lesser degree of damage and flaws in coal and rock materials. Therefore, this study suggests a data mining method for the correlation dimension to be applied in an in-situ monitoring system for rock mass excavation engineering.