The design of the cushion thickness for the dynamic-static combined drainage consolidation (DSCDC) technique has long relied on engineering experience due to the lack of a theoretical basis.To address this issue,the reinforcement mechanism of the DSCDC technique and the role of the cushion layer are first investigated.On the basis of a systematic analysis of representative engineering cases,the statistical relationships among the optimum cushion thickness,tamping energy,and the strength of the underlying soft soil are built.An impact model for stiff-over-soft double-layered foundation is built,and a theoretical equation for determining the optimum cushion thickness is derived by simultaneously considering the dual objectives of protecting the underlying soft soil and ensuring effective transmission of impact energy.Quantitative ranges for the key design parameters are also given.On the basis of engineering cases,a systematic design procedure for determining the cushion thickness of the DSCDC technique is proposed.The results indicate that the optimum cushion thickness is positively correlated with the square root of the tamping energy and negatively correlated with the undrained shear strength of the underlying soft soil.The cushion thickness should be designed by comprehensively considering the maximum allowable impact stress ratio,stress diffusion characteristics,and the configuration of the drainage system.The findings can provide both a sound theoretical basis and practical guidance for optimizing the design of DSCDC technique.