Investigation on evolution of rock fractures based on acoustic emission bywaveform energy spectrum

Based on the three-dimensional acoustic emission monitoring test of white sandstone with prefabricated crack, the fracture propagation direction was determined by the spatial energy distribution of acoustic emission waveform, and the fracture evolution characteristics of white sandstone under uniaxial compression were studied.Short-time Fourier transform (STFT) was used to obtain the energy spectrum of each channel waveform, and the direction of microfracture was represented by the direction of the smallest energy channel to the largest energy channel.The energy intensity was used to represent the fracture length.The results show that the fracture propagation of white sandstone is mainly parallel to the principle stress direction and the theoretical conjugate shear plane direction.In the initial compaction section and elastic section, the fracture is dominated by a certain direction.Starting from the fracture deformation section, the fracture proportion in the three directions gradually converged, and tended to be 30% in the pre-peak softening section.It is also found that the AE vector is clustered along the main fracture surface.Shear zone running through the rock sample is formed in the pre-peak softening section, which is considered as a reliable critical precursor to rock failure.