Settlement performance of pad footings on soft clay supported by stone columns: A numerical study

The settlement behaviour of small loaded areas (such as pad and strip footings) on soft soil supported by stone columns is poorly understood. The lack of confinement associated with peripheral columns and the sharp stress decay with depth are features which are incompatible with the widely-used unit cell method for infinite column groups thereby rendering small group behaviour particularly difficult to analyse. Useful field data is virtually non-existent and although innovative laboratory modelling has been insightful, the findings cannot easily be extrapolated to field scale. In this study, a 3-D finite element analysis in conjunction with an elastic-plastic soil model is used to identify the effect of variables in the design process and interactions between them: these include column arrangement, spacing, length, and Youngs modulus of the column material. A simplified method is proposed to relate the settlement of small groups to a reference unit cell settlement predicted by current analytical approaches.