Abstract: Pavement performance in widened roads has been a great concern for highway engineers in road-widening-related design and construction projects in western China since the fast implementation of West Development Strategy several years ago. The 3D finite element method (FEM) was used to simulate the construction and operation process of flexible pavements with Plaxis 3D Tunnel, a geotechnique-tailored commercial software. Elasto-plastic properties of materials as well as the filling process of subgrades in widened sections and critical placements of traffic loading were considered in the simulation. In particular, the non-uniform settlement behavior over newly-built and existing subgrades was assessed to explain premature damages of pavements commonly found in widened-road sections. Transfer functions were also used to predict the influence of widening subgrade sections on pavement responses. At the end, recommendations are made for design-construction based on results of numerical simulation.