Foundation Treatment in Karstic Limestone: El Cajon Hydroelectric Project, Honduras

Abstract

The El Cajon Project, completed in 1985, provides the necessary hydroelectric energy to relieve Honduras of the need for importing oil for generating purposes. The existing interconnection with Nicaragua and Costa Rica allows Honduras to export electricity on demand using the new facility. Steps are being taken to construct transmission lines to both Guatemala and El Salvador and thereby develop a regional electric inter-tie system. Construction began in 1980 following nine years of effort that included a final feasibility study, field investigations, design, and procurement of the necessary financing. One of the major aspects of the project was the treatment of the limestone foundation that contained solution features and large caves. Because of the geologic relationship between the limestone and nearby volcanic rocks upstream, the geometry of the grout curtain is unique. The curtain, developed by grouting between adjacent galleries, begins at the dam, enters the abutments and then curves upstream to close against the volcanic rocks. The curtain is therefore vertical in the abutments with a transition to a nearly horizontal plane beneath the river. The overall shape is similar to a bathtub with the back of the tub open to the reservoir. A comprehensive monitoring program was initiated when impoundment began in 1985 and will continue for several years. Measurements of seepage, pressures, and displacements are made regularly with periodic review by outside consultants. At the time of this writing, the reservoir is 80 percent full and the performance of the foundation is considered to be satisfactory.