Assessment of state of earth dam of Elchovka settling pond by combination of electromagnetic soundings and polarization methods

Abstract

Earth dams are constantly under the hydraulic pressure. Their long-term operation leads to arising of zones of increased water cut and filtration in body and base of dams. This weakens dam’s strength. Geophysical methods can be used to control condition of the soil structures. We describe the research results of the Elchovka earth dam by a complex of electrometric methods, as they are most sensitive to changes in soil moisture. We applied the self-potential (SP) method, the vertical electrical soundings (VES) and the remote induction soundings (RIS) with the study of the frequency dispersion of electrical resistivity. Main pathways of the water filtration were identified by the self-potential method. According to the results of RIS, the boundary between bulk and natural soils as well as the boundary between sedimentary and bedrock are clearly distinguished. Electric soundings on direct current (VES) allowed us to localize places with reduced resistivities due to increased soil moisture. Frequency dispersion anomalies, which can also indicate water filtration in bulk soils and bedrock, were found. On the investigated dam, anomalies of the electrical conductivity and the frequency dispersion coincide with anomalies of the self-potential. This indicates increased filtration. Thus, the use of the remote induction soundings and the frequency dispersion methods together with widely applied VES and SP methods enhances the reliability of research and provides additional information about the hydrogeological situation in the area of the dam.