Investigation of the Characteristics and Evolution of Seepage Field Distortion in Dams Induced by Core Wall Leakage

Abstract

Core wall leakage is a common seepage-related defect occurring during the operation of core wall dams. Clarifying the characteristics and evolution of seepage field distortion under leakage conditions is an important basis for assessing dam safety status and evaluating leakage risks. In this study, short-duration, small-scale physical model tests of an asphalt concrete core wall dam were conducted under leakage heads of 14 cm (S1) and 20 cm (S2) to characterize the spatial response of the seepage field. Finite element simulations were subsequently validated against the experimental results and extended through parametric analyses of leakage channel widths of 1–10 mm and burial depths of 5–29 m. The experiments showed that the distortion profiles on horizontal sections were approximately semi-elliptical, with the maximum extent occurring at the elevation of the leakage center and progressively decreasing with vertical distance. The maximum dam-axis diffusion width increased from 9.00 cm under S1 to 11.05 cm under S2, while the maximum streamwise diffusion distance increased from 4.70 to 6.00 cm, corresponding to increases of 22.8% and 27.7%, respectively. Three-dimensional reconstruction further showed that the distorted region exhibited a quasi-semi-ellipsoidal morphology centered on the leakage location. Quantitative comparison between the experimental and numerical results yielded MAEs of 1.325 and 0.550 cm, RMSEs of 1.506 and 0.628 cm, and MAPEs of 18.01% and 13.90% for the dam-axis diffusion width and maximum streamwise diffusion distance, respectively, indicating that the numerical model captured the observed spatial response with moderate quantitative discrepancies. Engineering-scale simulations further showed that increasing leakage channel width generally enlarged the distorted region, whereas the effect of burial depth was non-monotonic and controlled by the downstream phreatic surface. Above the phreatic surface, seepage field distortion increased with leakage channel burial depth; once the leakage channel reached or extended below the phreatic surface, the distortion weakened with further increases in depth. These findings quantitatively characterize the spatial response of the internal seepage field to local core wall leakage and provide a physical basis for interpreting leakage-induced anomalies in seepage monitoring of core wall dams.