The project was unique in the fact that the jacking pipe and the existing shield tunnel, which had the same diameter, were connected at the lateral juncture – a rare occurrence for pipes of equal diameter.
The road above the rainwater main experiences heavy traffic, and as such, materials for the job had to be transported by crane to the bottom of the starting shaft and were then passed sideways through to the jacking point.
The length between the starting shaft to the TBM-driven main pipe (Naruo No.2 Rainwater Main) was 630 metres – Japan’s second largest pipe jacking project.
The pipe jacking machine used in this project was a segmented and recyclable jacking machine, referred to as Yadokari-kun, or hermit crab. The machine has a movable hood attached to the top and bottom part of the machine to laterally connect the existing tunnel.
Article continues below…Construction process
After reaching the existing main pipe, the cutter spoke of the pipe jacking machine was shortened so that the spoke could be drawn back to the starting shaft. The front edge of the movable hood was then removed to fit the existing pipe and construct the connecting part. A steel support was installed in the existing pipe, and the segment lining was replaced with concrete lining.
Important considerations for this project included:
* Using the large diameter jet-grouting method due to the urban surroundings, and treating the ground around the bottom of the existing pipe; * After the internal lining of the existing main pipe was cut, concrete walls were broken into small pieces with a jack so that the pieces could be transported out of the manhole; * A steel framework was applied at the aperture of the existing pipe to support it structurally; and, * Use a good jacking-management system, contributing to the accuracy of the installation.
Design and development of the unique machine used was another major element in the success of this installation - the pipe jacking machine had a movable hood and the core parts of the machine, such as the cutter spoke and motor, were able to be pulled back to the starting shaft. Man-entry was also available at the front face of the machine.
Adopting a movable hood at the connection site and reusing the jacking machine were the major keys to the success of this project.
