Energy characteristics of infrasound abnormality during rock deformation and failure of rock

Eight groups of axial compression tests on sandstone are conducted in laboratory. The infrasound signals of each test process are recorded synchronously, and then the energy characteristics of each specimen are analyzed using the wavelet decomposition method. The results show that the infrasound energy of rock failure is mainly concentrated in two frequency bands. One is the medium frequency band with frequency range of 3.91~7.81 Hz, and the other is the high frequency band with frequency range of 7.81~15.62 Hz. The energy of the former is higher than that of the latter. At the same time there still exists a certain amount of energy with frequency range of 0~3.91 Hz in the signal. By comparing the energy distribution in different frequency bands, the infrasound of rock deformation and failure can be recognized. With the increasing degree of rock deformation, the energy with medium and low frequency bands decreases, and the energy with high frequency band increases relatively. When rock failure is coming, the ratio of the energy in medium and low frequency bands to that in high frequency band is near 1. The discovery of the above characteristics of infrasound during deformation and failure of rock may provide an important basis for recognizing infrasound signals and failure warning of rock.