Delineation of leakage pathways in an earth and rockfill dam using multi-tracer tests

Abstract

In this study, a multiple tracer analysis was carried out to investigate the leakage pathway of the Xixiayuan dam, located on the Yellow river in China. Composite geomembrane and a concrete cutoff wall are used jointly to control seepage. Filling of the reservoir began on May 30, 2007, with water level rising to 133.6mASL (Above Sea Level) on October 2, 2007. Thereafter, the water level fluctuated between 133.0m ASL and 133.6mASL until a leakage point emerged on October 15, 2007. From October 16 to 18, 2007, two other water leakage points were found emerging from the top of a drainage channel located at the downstream toe of the left earth rockfill dam. To determine the possible leakage pathways, 10 additional investigation boreholes were installed. Single-borehole artificial isotope dilution tests were carried out to quantify the vertical and horizontal flow velocities in boreholes at high and low reservoir water levels. Temperatures and water levels were measured in boreholes, reservoir water, and leakage points. An interconnection test using salty water tracer was performed between borehole and leakage point. As a result of these studies, the possible seepage location was identified to be near boreholes ZZ5 and ZZ6. Excavation and inspection at the estimated seepage location confirms the presence of a construction defect.