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 segments
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.
Dustless shotcrete method
With the dustless shotcrete method, the centrifugal force generated by a rotating disk (impeller) is used to blow shotcrete onto the wall of a tunnel. Because compressed air is not used, the amount of generated dust can be decreased down to between 1/20 to 1/30 of what is normally experienced and a good working environment can be maintained.
Backfill shield method and Re-cube mole method (for removing installed cables and pipes without excavating the ground)
In urban areas cables and pipes are densely laid in the underground spaces. Many of the tunnels that contain these cables and pipes are becoming superannuated requiring renovation or replacement as they reach the limits of their capacity. Using the backfill shield method, the ground close to an existing tunnel can be excavated using backfill shield machinery while at the same time earth can be filled back into the existing tunnel. Using the Re-cube mole method, a medium-or small-sized tunnel can be renovated using either the sheath pipe method, the pullout method, the crushing method, or a combination thereof.