An estimation method for predicting final consolidation settlement of ground improved by floating soil cement columns

Ground improvement using floating soil cement columns with shallow stabilization is an effective technique for the treatment of deep soft soil layers under infrastructure embankments. In order to investigate the settlement performance of this improvement technique, model load testing of model column analogues for visualization of ground behavior under plane strain conditions was performed and field observations at full scale test embankments were investigated. The results of model testing and field investigation show that the ground below an embankment founded on a floating column system can be considered as two separate layers with a confined portion and a consolidating layer which can be related to the degree of improvement used at a particular site such as the improvement ratio and the depth of improvement. A simplified estimation method for final consolidation settlement is proposed using a stress distribution ratio which considers the contribution from skin friction at the surface of floating columns. The advantage of this method is that is possible to determine the consolidating layer thickness as a function of simple parameters such as the degree of improvement, loading conditions and undrained soil strength. The predicted settlements of the improved ground correspond well to that measured in full scale case studies.