A New Explanation of loading Rate Effect on Rock Compressive Strength

Abstract

Apart from several qualitative descriptions, such as the delay crack propagation and the difference in energy absorption, the involved mechanism of loading rate effect (rate-dependence) on unconfined compressive strength (UCS) of rock is not clear. According to the statistical analysis of the dominant frequency of acoustic emission (AE) waveforms, this work proposed a new explanation of rate-dependence on rock UCS from a micro failure perspective. The uniaxial compression tests, coupling with AE signals monitoring, of five types of hard rocks under different loading rates were conducted. The rate-dependence on compressive strength of various rocks was investigated comprehensively. By using batch processing and Fast Fourier Transform methods, the dominant frequencies of AE waveforms associated with rock failures were extracted and analyzed to explain the rate-dependence of rock UCS. The results show that, as the loading rates increase, the UCS of most of the rocks increase, while the AE waveforms with low dominant frequency released during the entire loading process significantly decrease. Moreover, the percentage of AE waveforms with low dominant frequency has a negative correlation with the rock UCS. The micro-tensile failures can be characterized by AE waveforms with low dominant frequency and its reduction can be responsible for the increase in the UCS with increasing loading rates. The proposed explanation provides a new and reasonable perspective on the rate-dependence of rock UCS based on its intrinsic property.