Experience of Using Dipole Electrical Sounding of the Rock Mass in the Chirkey Hydroelectric Power Plant Area to Monitor its Stability

For the first time in the practice of field observations in the area of the Chirkey hydroelectric power plant dam, the dipole method of continuous electrical sounding is employed. The aim is to study geodynamic processes in the rock mass near the mentioned high dam to develop new methods for monitoring hazardous geological processes of natural origin and anthropogenic nature. The observation results for the 2018 – 2019 period show that there is a correlation of K = –0.78 between seasonal changes in the reservoir water level and the apparent electrical resistivity with a time shift of data series by 45 days. The lagging of apparent resistivity variations behind the water level demonstrates the presence of a physically justified rather than a random relationship. Based on the time series analysis of apparent resistivity, large-amplitude variations were found, which suggests that the rock mass under study is in an unstable state. In certain periods, processes associated with inelastic rock deformation take place. They are accompanied by the emergence of additional fracture zones in the rock along which shear can occur. Anomalies of the uneven electrical resistivity of limestone accompanied by acoustic emission were also detected in laboratory experiments at the stage of inelastic rock deformation before its failure. Thus, the phases of apparent resistivity growth can be considered as the opening of fractures in the mass, while apparent resistivity decrease indicates their filling with water. This process can be accompanied by shearing along the fracture zone in the rock mass. Such shearing can be triggered by the operation of hydroelectric generators, their start-ups and shutdowns, as well as earthquakes and other natural phenomena. This method in combination with measuring instruments can be translated into practice for monitoring hazardous geological processes.