A significant amount of foam shield tunneling surplus excavation soil, which contain a foaming agent and a blow off inhibitor, has been produced on shield tunneling construction. To utilize the surplus soil effectively for reclamation of harbor areas, engineering properties of the mixture of the surplus soil and steelmaking slag, which is an industrial byproduct in steel manufacturing, have been studied. Issues regarding the putting of the mixture in water was studied in this study. Two types of water putting ways were investigated through small-sized laboratory model experiments. One way was to put from the bottom of a water tank; the other was to put from the water surface. Effects of the ways for configuration of the sedimented mixture, bearing capacity of the mixture and segregation of the mixtures were studied by the experiments. Results show that the configuration of the sedimented mixture and the steepest gradient are not affected by the putting ways. The maximum and average bearing capacities of the ground surface were larger when the mixture was put from the water tank bottom. The water turbidity was smaller when the mixture was put from the water tank bottom.