Seismic Design of Stage IV Raising, Los Leones Dam, Chile

Tailings dams can reach dimensions which place them among the largest of all embankments. They should be designed with the same care and concerns for safety and the environment as water storage dams. Los Leones Dam is a compacted earth and rockfill dam, now built to Stage Ill. It impounds copper tailings and a shallow “clear water” reservoir. In Stage IV, the dam will be raised to 650 feet above streambed. This paper provides details of the seismic design of the Stage IV raising, Nonlinear effective stress analyses were used to calculate deformations of the embankment and excess pore pressures in the tailings and saturated part of the dam. Predicted crest settlements formed the basis to select the final freeboard. The March 3, 1985 Chilean earthquake (MS 7.8) shook the Stage II Dam (354-foot high), which was instrumented at crest and toe with strong motion accelerometers. This makes Los Leones Dam one of only a few large dams with recorded seismic performance during a major earthquake. We used the 1985 records to calibrate a numerical analysis model of the raised dam.