Sand Densification by Piles and Vibroflotation

The effectiveness of compaction piles and vibroflotation in densifying 30 ft of loose to medium dense sand fill at Treasure Island, California was evaluated by field tests. Compaction piles were installed by driving a 14-in. diam steel pipe mandrel with a false bottom to the required depth, filling the pipe with sand and then withdrawing the pipe to leave a sand column. Relative density of the fill was measured before and after densification by standard penetration tests and samples obtained with a piston sampler. Conclusions based upon results of the testing program are: (1) Both compaction piles and vibroflotation are effective in densifying sand fill if proper spacing is used; (2) vibroflotation produces a more uniformly dense fill; (3) compaction piles must be spaced closer together than vibroflot points to produce the same relative density; and (4) limited cost data indicates vibroflotation is more economical than compaction piles in cost per cu yd of compacted soil.