Abstract: The composite foundation is a common method for treatment of soft soil subgrade. The accurate calculation of settlements of composite foundation is of great significance for differential settlement control of new and old roads. Based on the widening project of Huai'an-Jiangdu Expressway, the CPTU tests and pressuremeter tests on the foundation of the new and old roads are conducted, and the tangent model for the soil is obtained according to the pressuremeter tests. The settlements of the reconstructed and expanded subgrade are monitored, and the compression modulus of the subgrade soil layer is back-calculated through the settlements of subgrade. The model for calculating the settlements of the composite foundation using the parameters of the CPTU tests is studied and compared with the traditional empirical relationship model. The results show that the proposed model can accurately calculate the settlements of subgrade, and the calculated results are close to the measured settlements. The proposed model is obviously superior to the traditional empirical relationship model, and it is recommended to use in the settlement calculation of composite foundation.