DESIGN AND IMPLEMENTATION OF A GROUT PROGRAM IN AN EVAPORITE-KARST FOUNDATION, RED BLUFF DAM, ORLA, TEXAS

Red Bluff Dam is a high-hazard, 9,000-foot-long embankment dam located in west Texas on the Pecos River. The dam and reservoir it impounds are owned and operated by the Red Bluff Water Power Control District and provide irrigation water for seven irrigation districts in the area. Construction of the dam began in late 1934 and was completed in 1936 under the engineering supervision of the Public Works Administration. Impoundment of the reservoir began in late 1936. Soon after initial filling of the reservoir, extensive seepage was noted at various locations along the toe and on the downstream slope of the dam. The District performed grouting operations in 1973 and 1978 to address seepage through multiple zones of the foundation. The geology of the site includes the Permian-age Rustler Formation (dolomite, gypsum, and shale at the site), and Quaternary deposits of weakly to strongly cemented sand, gravel, and clay. Extensive collapse structures resulting from dissolution of layers of evaporites (salt and/or gypsum) in the underlying Rustler, Salado and Castile Formations exist within the dam foundation. Site investigations were performed in 2012 and 2013 that included geologic mapping, core drilling, and piezometer installation. Data from these investigations, combined with existing data from previous grouting operations and site investigations were used to develop a comprehensive geologic model of the site and to design an effective grouting program aimed at mitigating the most critical seepage zones. The grout program was designed, and contract documents were prepared based on data from previous studies and grouting programs, as well as 2012 and 2013 site investigations. The grout-program criteria were to provide optimal grouting of the dam foundation while protecting the embankment dam. Grouting began in February of 2014 with the Judy Company as the contractor and was completed in January of 2015. This paper will present details of the grout program, geologic conditions encountered during grouting, revisions of the grout program based on field conditions to maximize the effectiveness of the foundation grouting, and the use of data from the grout program to develop additional treatment measures for ongoing seepage mitigation for the dam.