Project Story

General view

Main NEWJEC work on the Yamatogawa Route

Plane view of Route 6

Digging a tunnel under the city center involves coordinating various buried utilities: power lines, gas lines, water lines, telecommunications lines. Shigeji Yoshinaga, tunnel expert on the Yamatokawa Route project, reflects:
"At a diameter of 12 meters, the tunneling shield for the Yamatogawa Route tunnels is way larger than utility service tunnels. It was a real challenge thinking of how to build such large tunnels along the Yamato River. For example, the Osaka Metro Midosuji Line passes close to the Joban exit. How should we keep them from interfering with one another? How should we plan the road alignment and depth? What size structural members would we need to ensure strength? Finding the right answers proved very difficult as we went through the few domestic examples and literature grasping for clues in the structural planning. We also worked on the excavation tunnel design for the Amami shielded shaft section where digging would be carried out to a depth of 29 meters, close to the path of the Kintetsu Minami-Osaka Line. The circumstances called for ingenuity; we analyzed for subsidence and other impacts to the ground surface and used an earth retaining wall with members to reduce deflection. In the box culvert sections, we had to appropriately model the complex changing structure for the connection geometry between the traffic lanes and off ramps (sectional width, depth, ramp plane positions, etc.), which went from a double box to a triple box to a quad box. After evaluating with the seismic coefficient method, we designed the structure to ensure seismic resistance.
In all of NEWJEC history, I think it's the first time we've planned and designed a road tunnel of this scale. We did that, with our own hands. It was a great sense of achievement."

There are two types of tunnels on the Yamatogawa Route.

"In my almost 20 years working on the Yamatogawa Route, the most difficult part was tunnel disaster prevention. There were very few domestic examples to draw from, and we did not have any experts among us. Under the circumstances, we needed to establish a disaster operation plan." -Takashi Mizuguchi
How does smoke spread in large-scale blazes in a long underground tunnel? How do you keep people safe in such situations? What equipment is needed and what procedures should be followed to evacuate? Junji Kawasaki simulated various considerations and created evacuation guidance scenarios.
"The Yamatogawa Route has the first tunnel in Kansai to employ an evacuation slide. Originally, we were thinking of evacuating people to the tunnel running parallel for opposing traffic. With more safety considerations made, however, we changed over to having people evacuate by dropping under the road within the tunneling shield hole and using a shaft connecting to the surface. The change was made in 2017. There were only three years to the tunnel opening for service, and we didn't have a set design criteria or any drawings to work with. With that we held repeated discussions between the NEWJEC members and clients, poring over relevant literature and domestic and international cases. Our issue was how to verify our expected evacuation timeline: with the tunnel still under construction, no verification testing was possible. What I proposed was to use the distinct element crowd behavior simulator, a joint research project with Dr. Hitoshi Gotoh of Kyoto University, who I know from my graduate school days, to analyze the movement of people during a fire. In this simulator, evacuees and rescuers can freely act in a three-dimensional VR space. We checked for crowding points and calculated the time it took for them to evacuate underground from the fire and reach the surface via the complex underground space. From this, we were able to create a highly accurate timeline and verify our evacuation guidance.
After the tunnel was completed, we verified the results through actual field testing. For the field testing, we had stakeholders alongside kids and elderly from the general public evacuate as if an actual fire occurred. It was a big relief when the evacuation went safely and smoothly in line with the expected timeline. Every day was a slog, but doing something unprecedented like this with no manual made it that much more satisfying to complete. I remember telling the client, 'This is the first real engineering work I've done in years!' It was an engineer's dream come true."