3D DCIP Techniques for Detection of Internal Defects in the Älvkarleby Test Dam

This study explores the effectiveness of combining Electrical Resistivity Tomography (ERT) and Induced Polarization (IP) for identifying internal erosion processes in embankment dams. A small-scale test dam was built in Älvkarleby, Sweden, with deliberately embedded but undisclosed defects to test monitoring capabilities. Daily ERT and IP measurements were collected during 4.5-year years, and analysed using 3D inversion. ERT provided higher spatial resolution, while IP supported the detection of key subsurface anomalies. Two intentional core defects, one vertical and one horizontal crushed rock zone, were clearly identified early in the monitoring period by both methods. A third defect, a concrete block, was also detected but with slight spatial offset. After three years, an area near a wooden block showed high resistivity and low chargeability, interpreted as severe internal erosion. A defect near the abutment remained undetected, likely due to resolution limits. Several additional anomalies not linked to intentional defects were revealed, interpreted as zones with anomalous leakage and possible internal erosion which is supported by documented observations made when the dam was demolished. These results highlight the complementary strengths of ERT and IP for erosion monitoring.