In view of the problems of low shear strength index of soft foundation in large gap such as fluid mud and silt soil layer,difficulty of anti-sliding stability and settlement control,which can not meet the requirements of closure,this paper studies the closure scheme of fluid mud and fresh silted soft soil foundation of Hengsha Dongtan Circle(Phase 8)project.Based on theoretical analysis and numerical simulation calculation method,it proposes the combined foundation treatment method of drainboard installation in deep mud,thin layer mud gravel replacement and long bag reinforcement at the same gap.The strength of gap foundation soil is greatly improved in the short term and meets the closure requirements.The research results can provide new ideas for construction design of similar projects.