Telecommunications shield tunnels have a small inner diameter of approximately 2 to 3 meters, and the primary lining is made of steel segments in view of cost performance. A secondary lining is added for rust-proofing effects and to ensure efficient use of internal spaces. This secondary lining has been made of concrete which is poured on-site, but this creates the problem of long construction times. Therefore, NTT has developed a new construction method which greatly reduces the construction time. With this method, three-segment precast concrete components are produced at a factory and then assembled into ring form by a special assembly machine inside the tunnel. In addition, prefab internal facilities have also been adopted in order to further shorten construction times and reduce costs.
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