Comparative FEM analysis of deformation properties of expressway widening projects with cast-in-situ X-shaped concrete piles and circular pile

Based on the section S1 of Nanjing Yangtze River Bridge, a three-dimensional ABAQUS numerical model for composite foundation with cast-in-place X-section (XCC) piles and circular piles under widening road embankment is established. Meanwhile, the rationality of the numerical model is verified by the measured field results. The differential settlement between new and old roads with the addition of a new embankment, lateral displacement and pore stress between two kinds of piles are analyzed comparatively. The differential settlement and stress ratio between piles and soils, pile shaft force and shaft friction of combining section are also analyzed. The results show that the largest settlements and lateral displacements appear in the combining section and the bottom of new embankment slope respectively. The XCC piles have advantages in reducing the settlement and lateral displacement compared to the circular piles. The uniquely shaped section of XCC piles ensures that the shaft force and shaft friction are greater than those of the circular piles. The largest increase of the pile shaft force is 35%, thus the pile-soil stress ratio of XCC piles is approximately 42.5, bearing more than 46.6% upper road embankment than the circular piles. The XCC piles are advantageous when dealing with widening projects as they require short construction period and cause little settlement.