The Jackson Lake Dam was constructed in 1917 in the Grand Teton National Park near Jackson, Wyoming. The dam was a hydraulic fill placed on a natural alluvium and outwash foundation. The Bureau of Reclamation (Burec) determined that the dam and its foundation would be susceptible to liquefaction and failure during a potential earthquake; a series of contracts was let to remove and replace the dam with a compacted fill and to improve the dam’s foundation to depths of up to 110 feet (33 meters). After considering a number of options, the Burec selected deep soil mixing (DSM) as the method to improve the subsoils and to install an upstream cut-off wall.
A pre-job test section and extensive quality control testing was carried out, particularly related to the strength of the mixed soil. The results are summarized and reported herein. Significant conclusions reached from the testing program include:
– DSM samples continue to increase in strength for at least 112 days after placement.
– water cement ratio is the key determining factor in final strength, even more important than cement content.
– laboratory results run before the project conservatively predicted field results.
– wet mix samples generally have lower strengths than cores taken after the column set.
The DSM method appears to have great promise as a method for creating deep foundations, retaining walls, areal soil improvement and even underwater foundations. A rapid expansion in the application of this technology is likely for the U.S. market.