Levee work for No.3 unit in Ikata Nuclear Power Plant

An underwater concreting technique was decided to be used for preventing subsidence of a rubble mound which may occur after the installation of a caison. It was planned to fill the gaps among the rubble stones with a special type of underwater concrete. This report deals with the tests for concrete placing and actual levee work which was carried out based on the test results. Tests are performed to determine the compressive strength, flow properties and self-levelling properties of the concrete. Water analysis is also conducted. Furthermore, examinations are made on the capability of the mixer to be mounted on the vessel, the capacity of the concrete pump and required batches to be fed. A work plan is developed based on these examinations. The actual underwater concrete placing work was carried out as follows: 1) excavation of the foundation ground by a grab dredger, 2) throwing down of rubble stones around the foundation and compaction of them by a heavy weight, 3) shaping of the face of slope, 4) throwing down of additional stons in the central portion, and 5) placing of special underwater concrete. For quality management, measurements of the slump. slump flow and air volume were made and compressive strength testing was performed during the work. The tubidity is also observed. (Nogami, K.)