Effects of Vibroflotation on Clayey Sands

Results of tests, during vibroflotation of loose silty and clayey sands containing up to 30% clay, indicate that although significant increase in density can be achieved, the results are not as good as in clean sands and that there is a danger that vibroflotation might reduce the strength of any clays or dense clayey sands in the sub-soil. Field data are presented for five different saturated sandy materials from three sites. Satisfactory results are obtained with the use of the static cone penetrometer for checking the effectiveness of vibroflotation during preliminary tests and for subsequent compaction control. When crushed stone fill, instead of sand, is added to the vibroflot crater, compaction of saturated clayey sands is improved, but both the amount of compaction and the zone of influence of the vibroflot decrease with increasing clay content. The method of superimposing the effects of adjacent vibroflots, given by D'Appolonia, to predict compaction is shown valid for clayey sands. The use of the average cone penetration resistances to predict settlements after vibroflotation leads to overly conservative values.