Abstract：Due to the rapid increase of traffics，more and more early-built expressways will be reconstructed；and the control of differential settlements between old and new roadbeds on soft foundation is one of the key technical issues. Focusing on a typical soft foundation segment treated with dry jet mixing(DJM) piles in the Shanghai— Nanjing expressway widening project，the influences of pile length，pile distance，pile lateral friction force，geogrid and construction rate to the coordinated deformation between old and new roadbeds are analyzed with FLAC3D programme. The procedure is firstly analyzed for the influence of different pile lengths and distances on the deformations of soft foundation. Then，based on the proposed pile length and distance，the influences of pile lateral friction force with/without laying geogrid and construction rate are considered. The results indicate that pile length and distance are the most significant influential factors while the others are relatively minor ones. It is also shown that the excess pile length has little effect on settlement reduction；and excess pile distance can not meet the settlement control standard. It is suggested that the rational pile length is to ensure piles embedded in supporting soil layer about 2.5 m，and the rational pile distance is about 1.1 m. If actual pile lateral friction force is not 50% lower than the designed value，the influence is comparatively small on post-construction and differential settlements. Considering laying geogrid over the soft foundation treated with piles and pile caps has not distinct improvement on differential settlements；and the construction rate has potential influence on settlement rate but little influence on accumulated settlements with a loading rate of 10 kPa/d. According to the above results，an optimized treatment scheme for widening soft foundation is advanced and adopted. The settlement monitoring results show that the numerical calculation results agree well with the actual settlements；and the settlements indexes can meet the requests of engineering design.
