Abstract: By using finite element method and theory of consolidation, rheology and damage, the post construction settlement of thick soft roadbed improved by surcharge preloading and vacuum surcharge preloading is calculated considering two in situ experiments in Guang Zhu Expressway. Calculation results show that the primary consolidation of underlying stratum and the second consolidation of roadbed are major factors of the total post construction settlement of expressway roadbed, so the post construction settlement must be controlled in foundation improvement.