Long-term monitoring of rock mass using electrical resistivity tomography and high-frequency active seismic methods at the Bukov Underground Research Facility

Abstract

Long-term monitoring of the rock mass parameters near the underground excavation at a depth of 550 m was carried out in the Bukov Underground Research Facility (URF). A series of measured parameters exceeding two years were acquired. Apparent resistivity was measured by the electrical resistivity tomography (ERT) method with 48 electrodes on a profile length of 11 m. High-frequency active seismic measurement was implemented between one source and three registration sensors at 30, 60 and 90 cm distances in the central part of the ERT profile. The measurements showed that the apparent resistivities and seismic wave parameters exhibit a one-week periodicity related to the weekly regime of the mine ventilation. From the estimation of the depth range of the methods used, it can be concluded that the rocks near the excavation are fractured, and their water saturation regularly changes up to the depth of the first meters due to the mine ventilation schedule. The intensity of the weekly periodicity varies seasonally. In the case of seismic measurements, seismic waves' attenuation increases during the switched-off ventilation period. The weekly apparent and inverted resistivity periodicity shows a significant positive and negative correlation with periods without ventilation. In the case of active seismic measurement, the highest sensitivity was found to the changes in the amplitudes and frequencies of body and dispersive waves. The presented research is unique, especially in the volume of measured and processed data from underground excavation site monitoring by simultaneous seismic and resistivity methods. The results bring new insight into measurement design and interpretation of ERT and active high-frequency seismic monitoring.