Based on numerical modeling combined with a practical engineering

the characteristics of consolidation settlement and deformation of the new and old road foundations are analyzed for an expressway widening project where the old road is unstable.Some analyses and discussions are made of the possible methods of ground improvement.The analytical results show that the settlements of the new and old embankments increase gradually with the decrease of the consolidation degree of the old road foundation

but the differential settlement decreases gradually.When the consolidation degree of the old road foundation is relatively low during the late course of consolidation

it is probable that the differential settlement decreases gradually.When the new road foundation is improved with the lightweight embankment method and the composite foundation method

the effects of the two improvements have their own advantages and disadvantages.The former method induces much more additional settlement of old embankment

but can control the differential settlement better

while the latter method induces less additional settlement of old embankment

but much more differential settlements when the consolidation degree of the old road foundation is comparatively low.