67 / 2021-09-14 00:09:05

Vector characteristics of electromagnetic radiation generated from rock fracture

electromagnetic radiation,fracture,directionality,monitoring

It is well acknowledged that the fracture of rocks is accompanied by electromagnetic radiation signals. And as a monitoring method, electromagnetic radiation has been rapidly developed with broad prospects, but the research on the vector nature of the electromagnetic field generated by rocks is relatively insufficient. Based on the self-developed three-axis electromagnetic antenna, this paper studies the vector characteristics of the electromagnetic radiation signal during Brazilian tests of granite. According to the significant correlation between acoustic emission, electromagnetic radiation and load drop, the three-axis signals corresponding to the main fracture are extracted. Signals on the three axes have obviously different waveform characteristics in the time domain but have similar distribution in the frequency domain. And based on the signal auto-correlation function and cross-correlation function, the difference of the signal energy and rise time of the three channels is obtained. The results show that the signals of each channel of the three axes can be regarded as the three components of the magnetic vector. According to the principle of vector synthesis, directional characteristics of electromagnetic signals received at different positions are studied. There is obvious correlation between the synthesized signals of different antenna groups, but the degree of correlation differs depending on the position. The directionality characterization mainly depends on the feature vector obtained by the maximum value and peak matching of the synthesized signals. Results show that the direction of the magnetic flux intensity generated by rock fracture tends to be parallel to the crack surface, and the measured signal intensity is greater in a direction closer to the direction parallel to the crack surface. Based on the vector characteristics of electromagnetic radiation, it provides a more convenient method for stress monitoring and lays a foundation for realizing the precursor electromagnetic radiation orientation in underground engineering.