Abstract: Apparatus comprising a vehicle such as a sledge containing a reel, bin, or the like, holding casing material folded flat, is disposed for travel immediately over an underwater object or piece ground to be covered and is towed by a surface vessel. Situated behind the supply of casing material, relative to the direction of travel, is a table comprising two hinged parts sloping down toward the bottom of the body of water, the lower of the two table parts being arranged to slide over the object or piece of ground to be covered. Concrete of plastic consistence coming from the surface vessel by means of a pressure hose is injected into the casing sliding over the table, the nozzle of the hose being inserted through an opening between the two edges of the casing material. This opening, which may be formed in a zipper by means of two zipper slides, is then closed by joining the two long edges to form the casing.