Solutions for settlement of subsoil improved with sand compaction piles and the vertical stresses acting on the sand compaction pile and the subsoil clay are presented. These solutions were obtained using a simplified method of analysis based on the unit cell concept and assuming that the composite subsoil deforms under one-dimensional confined compression. The solutions were shown to be identical to those of the equilibrium method by Aboshi et al. (1979) with the stress concentration ratio given by the ratio of the constrained modulus of the sand compaction pile to the constrained modulus of the clay. The accuracy of the simplified method was verified by the rigorous theoretical approach reported by Balaam and Booker (1981).