To create and renovate urban underground spaces, we have developed many new construction methods and techniques: namely the backfill shield method for removing existing shield tunnels, the P&PC segment method, which is an integration of the Re-cube mole and concrete segment methods, the ring lock segment method, the JUC method, the dustless shotcrete method, and so forth.
This method is used to create one new tunnel branching off from another tunnel or to join one tunnel to another tunnel without constructing a vertical shaft. By using this method, the effects of tunnel renovation or excavation work on the surrounding environment can be significantly reduced and the work period also shortened at the same time. With this approach, special segments are installed in the tunnel to be worked on first so that tunnel branching or joining work can be done using ordinary shield machinery.
P&PC segment method and ring lock
With the P&PC segment method, a prestress force is applied circumferentially or in the direction of the tunnel axis to bring installed segments into firm contact with each other thereby forming a solid tunnel structure. The P&PC segment method, which was developed to construct shield tunnels, is not only cost-efficient but also very effective for constructing tunnels in land subject to high inner water pressure or for tunnels that require high earthquake resistance (This method was awarded the Innovative Technique Award by the Japan Society of Civil Engineers.). Ring lock segments have tendons designed as guides to facilitate the tunnel member assembly process. Because they are made rigid so as to resist high inner water pressure, they are used as the lining for underground rivers, underground regulating reservoirs, shield tunnels, and so forth, to prevent floods from occurring in urban areas.