Determining rock damage strength with acoustic emission monitoring technique in terms of hurst exponent
摘要
In complex deep engineering environments, progressive rock mass failures, such as slabbing failure and deep fracturing, often pose significant threats to engineering safety, and the rock damage strength (σcd) is a critical threshold parameter to characterize the progressive failure process of rock masses. Thus, accurately identifying the σcd is one of the key tasks for achieving the early warning and short-term forecasting for geological disaster. Based on acoustic emission (AE) monitoring data, this paper proposed an overlapping sliding window improved rescaled range (R/S) analysis method to dynamically calculate the Hurst exponent (H) of AE count rate and AE energy rate time series. aiming to characterize the statistical characteristic changes during the evolution of rock damage. In addition, the uniaxial compression test was conducted on granite, sandstone, and basalt under five different strain rate conditions, and the evolution of the H-value during loading was analyzed. Subsequently, the σcd was determined by combining the physical mechanism of H variation. Finally, the value of the σcd obtained in terms of the Hurst exponent was verified with that determined by the crack volume strain (CVS) method. The results indicate that, under quasi-static loading conditions, the H-value in the AE count rate and AE energy rate sequences generally initially declines, subsequently rises, and finally reaches a peak during the whole damage stage. The smallest difference between H-based σcd and CVS-based σcd will be obtained when the Hurst exponent is represented by AE energy rate compared with AE count rate, AE cumulative count, and AE cumulative energy. The methodology proposed in this paper exhibits good applicability for hard rock under low strain rate, providing new insight into quantitative identification of rock mass instability and engineering disaster early warning.