The composite foundation with sparse piles is widely used in practice as a time-saving and effective way to treat soft soil. Considering the distribution law of skin frictions on capped PTC (prestressed thin-wall concrete pile) rigid piles

this study assumes that the distribution of skin frictions can be simplified as two triangles. Combining Mindlin-Geddes’ solution with Boussinesq’s solution

the formula of additional stresses of the sparse pile foundation can be derived under the full consideration of the radius of influence. In numerical cases

the ground settlement can be determined using the layerwise summation method. The authors compared the results from the traditional calculation method and the united solutions and analyzed the variation of calculated ground settlement using united solutions while the pile spacing varies. The proposed combined method is used to analyze the settlement of the sparse pile foundation for ground treatment. The results show that the calculated settlement is smaller than that from the traditional method and fits well with the monitoring results. When the pile spacing is eight times larger than pile diameter

as the pile spacing increases

the additional stress field shows no significant variation but the settlement increases accordingly. For foundations with a large pile spacing

the utilization of the long-short-pile composite foundation is preferable. With the installation of deep cement mixing piles

the soft embankment can be reinforced and the ground settlement can be effectively reduced.