Abstract: In recent years, the construction of regional airports in mountainous areas is increasing. The high-fill engineering projects have large fill volume and use local materials, which contain soil, sand, rockfill materials and other geotechnical materials. Accurate prediction of the post-construction settlements of hill-fill foundations affects the safety and normal running of the airports. Compared with those of clay, the properties of granular materials are often more complex, such as particle crushing. Most of the existing viscoelastic-plastic constitutive models are only for the clay, and cannot be directly used to calculate the rheological deformation of granular materials. A time-dependent unified hardening model suitable for granular material is proposed, which can describe the stress-strain-time characteristics of clay and granular materials in a unified way. The process to develop the new constitutive model in ABAQUS by using the user subroutine is given and implemented. Finally, the new model is validated through test results, including triaxial drained creep tests on clays and triaxial undrained tests on sand. It is shown that the model can well describe the stress-strain-time relationships of clay and granular materials.