Integrated high-resolution electrical tomography and drilling cascading investigation of earth-rock dam leakage in a siltstone region: A case study of the Maoshan Reservoir, China

Abstract

Piping, erosion at the contact of flowing soil, and leaching damage pose a serious leakage risk to earth-rock dams in the siltstone regions. With increasing reservoir operation time, seepage phenomena commonly occur in earth-rock dams, leading to progressively severe damage to the dam body. To understand the distribution of seepage in an earth-rock dam, including its location and magnitude, an imaging analysis of the dam structure is necessary. This involves determining the leakage positions and the underlying reasons. In this study, we conducted a high-resolution electrical resistivity tomography (HERT) investigation to characterize the leakage conditions of the Maoshan Reservoir earth-rock dam in the siltstone area of Jiangxi Province. To enhance the reliability of the HERT data interpretation, drilling, and water pressure tests were employed to validate the interpretations of low-resistivity zones. By applying this cascading survey and analysis method, we obtained spatial variability information on the apparent resistivity of the dam. The resistivity imaging of the entire dam revealed significant variations in apparent resistivity in the study area. Low-resistivity anomalies and high-resistivity anomalies were observed on both the upstream and downstream slopes of the dam. These anomalies represent saturated water channels and impervious bodies, with resistivities less than 200 Ωm and greater than 700 Ωm, respectively. The results of this study indicate that a cascading survey combining HERT and drilling is effective for analyzing the leakage positions of earth-rock dams, providing valuable insights for engineers in implementing effective anti-leakage measures in siltstone area reservoirs.