Projects Using Cutting-edge Technologies

Case 2

Oi Area Tunnel Project, Central Circular Shinagawa Route (completed 2012)

New attempt that attracts global attention through unity

Masayoshi IZAWA Resident Engineer, Project Engineer (at that time)

Oi Area Tunnel Project, Central Circular Shinagawa Route
Large-Scale Construction Using New and Existing Methods

This project involved the construction of a road tunnel extending approximately 730 m from the overpass bridge connecting the Oi Junction, which is part of the Central Circular Shinagawa Route of the Metropolitan Expressway, to the Oi North Ventilation Station. It was a complex project using a wide variety of construction methods including the bridge superstructure and substructure, a pneumatic caisson to excavate the vertical shaft, and the main shield tunneling with one of the largest shield machines in Japan.

Unlike the usual shield tunneling method where a vertical shaft is dug at the starting point and the tunnel is excavated from underground, URUP method was used. The shield tunneling machine was launched from the ground, dug its way underground, reached the vertical shaft constructed with pneumatic caissons, changed direction 180 degrees in the shaft, excavated the tunnel again, and returned to the surface. It was the first practical application of URUP method in Japan. There was no example of URUP method used in overseas projects of this scale, so this case attracted international attention.

As the supervisory engineer of the project, I was in charge of overall construction planning, management, client relations, and others. I had mixed feelings of gratefulness and elation at being entrusted with the unprecedented challenge, pride as a professional in engineering, and pressure as a leader for successful completion.

URUP, a new construction method put to practical use

The URUP method, which does not require the excavation of vertical shafts at the launch and arrival points, shortens the construction period and significantly reduces the amount of soil generated during construction. In this project, construction soil and CO2 emissions were reduced by 40% and 54%, respectively, compared to open-cut excavation.

On the other hand, there were risks associated with launching from and arriving at ground level, such as tunnel uplift due to the groundwater, and deformation of the cross section due to unstable loads caused by small overburden.

We conducted demonstration tests in advance to identify issues with this method not found in theory. Furthermore, based on the findings of the tests, we obtained a technical review certificate, which led to the introduction of the method to the site.
Specifically, to prevent the tunnel uplift by groundwater, we stabilized the weight balance with temporary fill during construction and with heavy concrete for the tunnel structure upon completion. And to prevent the deformation of the cross section due to unstable load with small overburden, we reinforced the tunnel with temporary steel during construction and with the permanent reinforcing structure at a location that does not interfere with the road space upon completion.

Since this was a large-scale URUP project, the first of its kind in the world, we were busy attending many overseas visitors, including ones from New Zealand who were considering URUP method for the upcoming construction.

Masayoshi Izawa Resident Engineer, Project Engineer (at that time)
URUP expanded the scope of the application

The tunneling with URUP method started in February 2010. Overcoming challenges such as excavation in the locations with only a 30 cm gap between the tunnel and the buried infrastructure supplying electricity, the project was completed in May 2011. The method opened a new era of shield tunneling with shorter construction periods and reduced environmental impact.

The URUP method has literally opened the way to a new era of tunnel construction, greatly expanding the range of applications for shield tunneling. Accumulating achievements in the construction of roads that access from the surface to underground, the method is also used in a variety of other situations, including lifeline tunnels that cross rivers and the ocean floor.

Realizing the importance of solidarity once again

As a tunnel engineer, I observe phenomena carefully and capture the essence by making full use of my knowledge and experience. Perseverance is my policy and I believe in proceeding with construction work with integrity and certainty.

A large-scale project like this can only succeed with collaboration among all members. I try to communicate as clearly as possible so that we can work toward our aim based on a common understanding.

This project involved various types of construction methods including the new one, and we reaffirmed the importance of unity among our colleagues on site, in-house technical teams, and our subcontractors.
As a leader, I believe that I should set an example through my behavior. At the same time, when I thought about the meaning of drinking parties, I realized that, as the leader, I had to deepen friendships more than anyone else. So, I thought it would be better to promote close relationships between workers and gradually start to lose the restraints. Now some younger workers even trade quips with me.
I will keep this attitude toward my work, and I hope to pass it on to the next generation.

I want to be the one who implements "MAKE BEYOND”

The Obayashi Group's new brand vision, "MAKE BEYOND; Transcending the Art and Science of Making Things," happens to be very similar to what I have always had in mind.
“With the Power of Vision we see beyond tomorrow. Through the Power of Creation we transform ideas into tangible innovations. But it is the Power of People that makes everything possible.” With this motto in mind, I will continue to take on the challenges to "go beyond," empowering us to break the experience and technology of “making things” in a way that has never been done before.