A new FEM analysis procedure for the consolidation analysis of composite foundation, named PDSS approach, is proposed and programmed. A case of composite foundation with flyash-lime columns beneath highway is analyzed by PDSS approach and 2D FEM respectively. From the comparisons of the numerical results and those observed from field test, PDSS approach is proved to be more satisfactory than 2D FEM. The investigation on the consolidation behavior of the composite foundation shows that the settlement of the soft soil stratum beneath highway can be reduced significantly by the reinforcement with flyash-lime columns because the columns increase the stiffness of the whole foundation. Redistribution of stress in the composite foundation accelerates the dissipation of excess pore water pressure although the permeability of columns is smaller than that of soil. So the consolidation mechanism of flyash-lime columns is different from that of vertical drains.
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