A method has been developed for pouring hardened bottom mud into water. This method can be used for largescale projects at rates up to 1, 000m3/hr without polluting the seawater at the site. When it was first used for hardening and placing work in actual ocean water, 160, 000m3 was deposited in a short time at an average rateof 700m3/hr. Here, an outline and explanation of the advantages of this method are presented.
Next, it was proposed that this method be used as earth cover material to cover polluted sea bottoms, taking advantage of the fact that the hardened material can be poured without polluting the ocean. To verify that this use would be effective, elution testing of nutrient salts and the like from the hardened soft clay wasperformed. The results confirmed that it could be used effectively as earth cover material restricting the elution of nutrient salts from undredged material.
