Abstract: The analytical solutions of the equivalent deformation modulus and equivalent Poisson’s ratio of composite foundation on the stage of elastic deformation are developed according to the deformation consistent principle and considering boundary constraint conditions based on the unit cell model. The research results indicate that the equivalent elastic constants of composite foundation are related to the lateral restraint condition of the unit cell. The equivalent deformation modulus increases as the lateral restraint enhances, and the equivalent Poisson’s ratio has a reverse trend. The equivalent deformation modulus are respectively the upper and lower limit values; and the equivalent Poisson’s ratio varies with area replacement ratio greatly when the lateral restraint condition is strong. The results also show that the deformation modulus calculated by area-weighted method leans to small; and the compression modulus leans to large. Comparing with area-weighted method, the difference value of the equivalent compression modulus varies with area replacement ratio and increases as the oedometric modulus ratio enhances; the difference is up to 20%-30%

Key words: composite foundation, equivalent deformation modulus, equivalent Poisson’s ratio, replacement ratio