Rationalized construction of embedded structures in dam bodies constructed by the RCD method

摘要

In general, layered concreting methods for dam construction, including the RCD method, require a continuous cycle without making a vertical gap or a cold joint in a field. This is to secure quality and safety of the work, as well as to make the transversal movement of heavy equipment easier. Sometimes, however, this continuous cycle shall be suspended due to the construction of embedded structures, such as galleries, conduits, shafts, and rooms. Shortening the construction period of such structures and securing safety during such works are serious issues we have confronted during past use of the layered concreting method. Miyagase Dam is the highest and the largest RCD dam in Japan. This paper presents two examples of the many challenges overcome while constructing the Miyagase Dam. One is the adoption of pre-cast concrete members as permanent forms for the gate operation rooms, instead of conventional and time-consuming in-situ forms. This was an epoch making event because it has been necessary to minimize extraneous materials at dams before the Miyagase Dam was constructed. A significant time saving was reported, not only because on-site formwork periods could be eliminated, but also because dam concrete placement and the installation of gates could be scheduled simultaneously. This also made the installation of steel gates faster and safer than in the past, due to the relatively spacious working environment. The other is the adoption of pre-fabricated conduits. Each steel pipe was integrated with its supporting frame in the fabrication yard, carried to an appropriate position, and jointed using flanges instead of on-site welding. On-site welding was limited to that for waterproofing, applied from the inside of the pipes. Based on our experiences building the Miyagase Dam, we believe that those challenges could contribute to the earlier completion and greater safety of any layered concrete dam project.