A Diagnostic for Internal Erosion in Earth Dams Using Piezometric Indicators

Abstract

This study aims to assess seepage behavior and internal erosion in an earth dam using Time Lag (T_L) and Pressure Ratio (P_R) as diagnostic indicators. Piezometric head data from 2003 to 2024 were installed in the residual soil layer of the case study dam. The T_L values showed a decreasing trend over time, notably at OSP 10, where T_L dropped from 50 to 20 and then to less than 1 day in 2003, 2013, and 2024, respectively, indicating progressive crack opening and continuous seepage paths. P_R values suggested internal erosion levels ranging from Very Likely to Likely (P_R = 1.0–0.8, 0.8–0.6), with reduced risk beyond +80 m from the dam axis, reflecting downstream progression of erosion. The combined use of T_L and P_R effectively captures internal erosion behavior in both temporal and locations. The approach provides a reliable basis for early warning, maintenance planning, risk management, and long-term dam safety assurance.