Effects of Clogging on Settlement Predictions of Ground Improved with Stone Columns

Clogging of stone column (i.e., the mixture of column material and surrounding soil) is widely reported as well as its hindrance effect on the consolidation rate of soft ground improved with stone columns, however, its influence may be more complicated in settlement estimations. In this study, a modified consolidation model is proposed for making predictions of settlement with consideration of clogging. Its influence on permeability and compressibility is included while both radial and vertical flow in stone column are taken into account. Parametric studies reveal that the consolidation rate will be largely impeded if the permeability of clogged column drops below that of surrounding clay. The short-term settlement is lower mainly because of the reduction of permeability. On the contrary, the long-term settlement becomes larger due to an increase in compressibility. This finding implies that the final settlement may be underestimated if the clogging effects are not incorporated even when early field observations are available, as supported by a design example.