Tunnel Construction Professionals
Conventional Tunneling
General Manager, Tunnel Engineering Department, Civil Engineering Technology Division Obayashi Corporation Hideo KINASHI
Integration of Technology and Nature in Tunnel Construction
Characteristics of tunnel construction
Construction of tunnels involves digging a hole in the earth and supporting the excavated ground with concrete and/or rock bolts. Unlike in other civil engineering works such as building of dams and bridges, the tunnel may collapse at the face (the foremost part) in some rare cases as the ground itself is a part of the structure that keeps the tunnel space open.
Safe construction of tunnels while producing a quality finished product and protecting the surrounding environment requires a wide range of knowledge and skills --- not only in the construction materials, explosives and heavy machinery used, but also engineering, hydrology, geology and rock mechanics.
Evolution of Technology in Tunneling
From 1990 to 1995, Obayashi researched and developed various technologies in ground characteristic modeling and monitoring, and various construction methods at an underground cavern in the Kamioka Mine in Gifu Prefecture. At that time, the underground site was the only place available to conduct large-scale experiments like displacement monitoring of actual ground during blasting under the same conditions as at construction sites. The results of the experiments became the basis of today's technology. Since then, we have been conducting research in the various fields of tunnel construction mentioned above, particularly in survey and countermeasure techniques for unstable ground conditions and research and development of lining concrete, which demands a high quality finished product. More recently, we have been focusing on the introduction of AI and the automation of construction machinery to improve productivity and to solve a skilled labor shortage in the industry.
Obayashi’s biggest asset: on-site capabilities
In addition to the technological development, what Obayashi values above all is on-site capabilities. From early on, our employees gain experience in the field, especially in tunnel construction, working at the tunnel face, learning ground monitoring and evaluation, and all of the tunnel construction means and methods in detail. Through hands-on experience, they understand all the processes to completion and acquire the ability to do their job quickly and accurately.
Great examples of Obayashi’s on-site capabilities are especially seen at emergency restoration projects of major infrastructure such as the Uonuma Tunnel on the Joetsu Shinkansen (high-speed rail system) and the Sasago Tunnel on the Chuo Expressway. As both were important infrastructure, there was no time or work to waste. Veterans and the young worked together as a team by communicating with all project stakeholders, developing plans, and making on-the-spot decisions to accomplish the restoration. I could see the results of the staff’s daily efforts.
The founding spirit passed down
Obayashi Corporation was founded in 1892 by Yoshigoro Obayashi, the second son of a marine products wholesaler in Osaka. Obayashi had already undertaken a number of major projects in those times, one of which was the construction of the Ikoma Tunnel for Osaka Electric Tramway (now Kintetsu Railway). This large-scale project involved tunneling through Mt. Ikoma where the geology was complicated and high groundwater inflow was expected. During the construction, the bedrock collapsed, making it an unprecedentedly difficult project. After the accident, the construction was forced into a difficult situation due to a lack of funds from the owner. Yoshigoro said, "I'll lend you money for the construction expenses. Let's put our hopes in the future and strive to achieve the goal.” He then put in a large sum of his money to complete the Ikoma Tunnel. The Ikoma Tunnel became the longest double-track tunnel at the time and was called "the longest double-track tunnel in the Orient," which was a major undertaking in Yoshigoro's later years.
Even today, each and every one of Obayashi's employees carries on the will of Yoshigoro: "Never cut corners even in difficult situations and use the best materials to achieve the best possible construction.”
Further Development
While we need to keep updated on technological innovations in tunnel construction such as AI, automation of machines, new technologies and materials developed around the world, we also need to keep our focus on the basic engineering research in geology, rock mass and other disciplines.
Acquiring deeper knowledge of the ground, which is part of the structure that supports the tunnel, is crucial in developing and utilizing new technologies.
Mountains are a part of nature, and we don’t have 100% control over them. There are always chances to experience ground water inflow or rock falling during the tunneling. But when we figure out how to work with the mountains, tunnels will support our vital infrastructure.
I believe that people involved in tunnel construction must have a sense of awe and respect for mountains. We will remain humble in the pursuit of further development of tunnel construction.
