The traditional calculating method of composite modulus is based on the assumption of the displacement compatibility between the flexible columns and the surrounding soil. However

case histories of embankment on ground improved by flexible columns revealed that the magnitude of the settlement of surrounding soil is often larger than that of flexible columns. The traditional composite modulus method may under-estimate the settlement of composite foundation under embankment. A two dimension finite element method (FEM) is adopted to capture the displacement incompatibility between the flexible columns and the surrounding soil under embankment and to investigate the factors influencing the settlement of composite foundation. The composite modulus of reinforced zone is back-analyzed by the layer-wise summation method. Comparison of the deformation of substratum before and after flexible columns installation yields the modified calculating method for settlement of substratum. Hence

the FEM is related with the layer-wise summation method. A practical calculating method of settlement of reinforced zone and substratum is put forward

respectively. A case study is also presented for verifying the validity of the proposed method.