Mud Mountain Dam Concrete Cutoff Wall

by Richard D. Eckerlin, U.S. Army Corps of Engineers, Seattle, United States,

Document Type: Proceeding Paper

Part of: Geotechnical Practice in Dam Rehabilitation


Mud Mountain Dam is an earth and rockfill flood control dam on the White River. The dam is located approximately 50 km southeast of Seattle, Washington. The dam was constructed in 1941 across a narrow rock gorge with steep volcanic rock walls more than 85 m high on both sides. The dam is 130 m high and is composed of a central impervious core and symmetrical upstream and downstream transition zones and rock shells. Core material consists of a mixture of sand, gravel, and silty mudflow materials. Transition materials are 100-mm-minus crushed rock. In 1980, as part of a program to install instrumentation on the dam, a single observation well was drilled through the dam core in the deepest part of the canyon. From 1980 to 1984 water levels in the well were routinely measured. Over the 4 years, water levels were found to be increasing which suggested that deterioration of the core was occurring. Further investigations revealed that fine materials were being washed out of the lower part of the core. It was determined that the transition did not meet requirements for a graded filter. As a result differential settlement and cracking damaged the upper, more sandy, portion of the core. During 1989-90, Soletanche, Inc., constructed a concrete cutoff wall through the embankment core into the rock foundation. During wall excavation the contractor experienced severe slurry losses due to hydraulic fracturing. Soletanche's contract was modified to use remedial grouting techniques to close the soil fractures and recompact the saturated core material. The completed cutoff wall measures 246 m in length and varies in depth from 3 m on the abutments to 122.7 m in the deep canyon.

Subject Headings: Concrete dams | Rockfill dams | Soil settlement | Rocks | Hydraulic fracturing | Embankment dams | Diaphragm walls | Washington | United States | Seattle

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