Abstract: The consolidation equations and the corresponding solution conditions of the composite ground with floating stiffened deep cement mixing (SDCM) columns with long core piles are derived under an instant loading. On the basis of one-dimensional consolidation theory of a third-layer soil ground, the corresponding analytical consolidation solutions are developed, including the average excess pore water pressures within the surrounding soil and underlying soil and the overall average degree of consolidation of the composite ground. The correctness and accuracy of the proposed analytical solutions are verified by comparison of the consolidation rates by the proposed analytical solution and the FEM. Some main factors are analyzed to investigate the consolidation behavior of this type of composite ground using the proposed analytical solution. The results show that the consolidation rate of the composite ground depends mainly on the penetration ratio of the SDCM columns with long core piles and the stiffness of the underlying soil. It increases with increasing penetration ratio of the pile and the constrained modulus of the underlying soil. The variations in the length, thickness and stiffness of the deep cement mixing (DCM) column sockets as well as the area core ratio of the concrete core piles have little effect on the consolidation rate of the composite ground. An increase in the modulus of the core pile decreases slightly the consolidation rate of the composite ground at the early stage of consolidation process, and it affects insignificantly the consolidation rate at the later stage of consolidation.