The deformation characteristics of river embankments on soft ground, improved by circular deep mixed columns and a combination of circular and grid-form columns, were investigated via two centrifugal model tests. The results indicate that the slope stability of the river embankment was effectively sustained in both cases. The combined reinforcement method exhibited superior overall performance, significantly reducing settlement. The greatest settlement was observed at the top of the river embankment, and although the settlement had not fully stabilized one year after construction, the settlement rate had slowed. Compared with the circular reinforcement alone, the river embankment maximum settlement was reduced by 25.3% in the combined reinforcement. Additionally, the grid-form columns effectively reduced the horizontal displacements in the middle and lower parts of the foundation. The deep-mixed columns performed effectively in providing support and reinforcement, and none of the piles reached the bending capacity during the test process. Given the stiffness difference between the columns and the surrounding soil, the stress distribution exhibited a stress concentration effect in the model. The measured column soil stress ratio ranged between 2 and 3, which is considered reasonable. The pronounced stress concentration effect of the mixing columns contributed to a faster consolidation rate of the foundation. On the basis of the measured settlement and excess pore water pressure, the degree of consolidation of the circular column-reinforced foundation one year after construction reached over 90% and 80%, respectively. For the foundations reinforced with combined circular and grid-form deep mixed columns, the degree of consolidation reached over 80% and 75%, respectively.