Vibroflotation Compaction at Thermalito Afterbay

A test program using vibroflotation to density silty sands beneath surface day and silt layers is presented. Vibroflotation compaction columns were constructed along the downstream toe of an embankment dam at two locations. At one location, columns were placed through the dam crest. The sands treated contained between 5% and 35% fines. The test program and construction monitoring are described in detail along with the atypical construction procedure used in the program. Comparisons of before and after standard penetration test and cone penetrometer test results generally indicated no improvement after construction. Failure of the method to density the sand is attributed principally to the presence of significant amounts of fines in the sand.