PURPOSE: To greatly reduce the total cost of reclamation work by concurrently connecting an opening on the reclamation material side with an opening on the floating material side.

CONSTITUTION: At the place where the inside of a sandbag of a water-permeable bag 1 is divided into nearly two sections from an opening 4 toward the longitudinal direction, a seam 5 is provided or a partition film 6 is put in the inside. A reclamation material 2, e.g., gravel, etc., is put into one section to an extent that it sinks slightly in water, and also a floating material 3, e.g., wood chips, etc., is put into the other section. The opening 4 on the reclamation material 2 side and the opening 4 on the floating material 3 side are concurrently connected with each other. The consolidation and settlement of soft ground below the seabed are thus reduced and the improvement of the ground by sand drain work, etc., is also cut down. Therefore, the total cost of reclamation work can be greatly reduced.