A submerged jet can be utilized to excavate the sea bottom obtain a large quantity of sand buried under the bottom. Experiments have been conducted for the most foundamental case of a vertical submerged jet impinging on the horizontal surfaces of sand and gravel. The sizes and depths of excavated holes were measured for various combinations of jet pressures and nozzle diameters. It was found that the hole depth is determined by the jet velocity, nozzle diameter, and grain size, and a semi-empirical relation emong these quantities is presented in this report.
　At the same time, a prototype test of underwater excavation was made with the jet venturi drefger Hiryu-Go. The volume of excavated sand was almost proportional to the momentum of a jet, as expected from the rusults of model experiments.