Abstract：When a highway is built on soft clay，vehicles will bounce when they run through a bridge approach because of large settlement difference between a bridge and embankment. Jialichen Bridge uses a composite foundation of rigid piles with different length along embankment to reduce the settlement difference. Embankment weight is a kind of flexible load and prototype observation analysis is reasonable way to study composite foundation under embankment. The prototype observation shows that because settlement of soil is larger than that of piles，an arch effect appears in the embankment so that its weight is gradually transferred from the soil to piles and pile-soil stress ratio increases. Due to the composite foundation，two-thirds of natural foundation settlement is removed. It is more significant that the road surface is basically smooth because of the piles with different length along the embankment. The observation of settlement in different depth shows that larger deformation is developed in the layers nearby the stabilized layer bottom.
