Abstract: The composite foundation with combined stone columns and impervious piles can not only improve the bearing capacity of the foundation, but also accelerate the consolidation of soil, which has a strong application value in treating saturated soft clay foundation. Based on the calculation model of axisymmetric consolidation with bidirectional seepage, a consolidation differential equation of composite foundation reinforced by stone columns and impervious piles is established by considering the volume compression of central and peripheral stone columns and the disturbance effect of piles construction. The analytical solution of the combined composite foundation consolidation under the variation of additional stress with time and depth is derived by using the analytical method, including the solutions of average excess pore water pressure of stone columns and soil and the average consolidation degree of composite foundation. The correctness of the solution is verified by degradation study and comparison with existing solutions. Finally, a smaller additional stress at the bottom of the composite foundation, or a denser distribution of stone columns and impervious piles, will lead to a faster consolidation of the combined composite foundation. The disturbance effect of stone columns construction on composite foundation is greater than that of impervious piles. Ignoring the effect of the volume compression of stone columns will overestimate the consolidation rate of composite foundation; the smaller the radius ratio is, the larger the error will be. A good agreement can be observed between the predicted consolidation degree by the theoretical solution and the measured one.

Key words: composite foundation, bidirectional seepage, volume compression, additional stress, analytical solution