Settlement of floor slabs on stone columns in very soft clays

Abstract

Investigations of serviceability failures of building floor slabs supported by stone columns in very soft clays prompted a review of the methods for predicting the settlement reduction achieved by the columns. Data from both successful case histories and serviceability failures indicate that, in practice, settlement reduction for widespread loading of very soft clays may be both quite limited and overestimated by current design methods. Analysis of long-term settlement observations from two serviceability failures suggests that the reduction in secondary settlement achieved by the stone columns was also quite limited. Based on these findings it is considered that the range of loadings and thicknesses of very soft clay for which stone columns would be viable for widespread building loads is likewise limited. A review of the serviceability failures led to the conclusion that inadequacies in the procurement of the design and construction of the stone columns contributed to the failures.