In order to study the causes of post-construction settlement of deep-jet-mixed（DJM） pile composite foundation at bridge approaches

the settlement is analyzed and back-analyzed by Biot’s consolidation FEM.The soil constitutive model is the Duncan-Chang nonlinear elastic model in finite element analysis;and Duncan-Chang nonlinear elastic model and Merchant viscoelastic model are used in finite element back-analysis.The computation results show that the traffic load and soil creep are the main causes induced the post-construction settlement of DJM pile composite foundation.The traffic load is the main cause at early period

but soil creep is the main cause at post period.