Consolidation settlement of floating-column-improved soft clayey deposit

The interaction behaviour between a floating column and the surrounding soil, with or without a surface cement stabilised slab, has been investigated by laboratory model tests as well as finite-element analysis (FEA) using an axisymmetric unit cell model. Based on the test and the FEA results, a method for calculating the consolidation settlement–time curve of floating-column-improved soft clayey subsoil has been developed. This method has been modified from the earlier method of Chai and Pongsivasathit by treating a part of the column improved layer with a thickness of H_c as an unimproved layer in settlement calculation to consider the effect of possible penetration of the column into the soft soil layer below the column. An explicit equation for calculating the value of H_c has been proposed as a function of area improvement ratio (α), depth improvement ratio (β), load intensity (p) and the undrained shear strength (s_u) of the soft clayey soil. The validity of the method has been checked using the laboratory model test results as well as four field case histories in Japan.