Abstract: Compatibility of deformation between the existing embankment and widened portion is a common problem in widening projects. There is still a lack of direct comparative analysis of the influence of widening methods on the engineering characteristics of soft soil subgrade. In this study centrifugal model tests are conducted to investigate the widening styles of slope and retaining wall using ordinary or lightweight materials. The embankment deformations, pore pressures and earth pressures in soil are monitored during flight. The results show that using the foamed light-weight soil can significantly reduce the pore water pressure and additional stress increments induced by the construction of the widened portion. As compared with the slope widening, the retaining wall widening had less impact on the foundation. The inclination of the retaining wall and the earth pressure on the back caused by the foamed light-weight soil embankment are low. It is indicated that the additional stress distribution in soil because of the widening portion calculated with the Boussinesq's equation is conservatively in good agreement with the measurements. The research results are meaningful for guiding widening projects.