Japan’s Legacy of Underground Innovation : A Tribute to 50 Years of Excellence

Former President,
International Tunnelling and Underground Space Association (ITA) Prof. Arnold Dix

It is with great admiration and respect that we celebrate Japan’s extraordinary contributions to underground construction and tunneling over the past 50 years. Japan has long been a centre of excellence in underground engineering, pushing the boundaries of what is possible beneath the surface of the Earth. From its pioneering high-speed rail tunnels to breathtaking feats of deep, long, and even double-decker tunnel construction, Japan’s advancements have shaped the global industry. The country’s leadership in TBM innovation, air cleaning technology, fire suppression systems, underground transportation hubs, and flood mitigation infrastructure has set new benchmarks for safety, efficiency, and sustainability.

As President of the International Tunnelling and Underground Space Association (ITA), I am honored to recognize Japan’s groundbreaking achievements and its invaluable contributions to ITA’s working groups and global best practices. This is a nation that has built not just tunnels, but pathways to progress—engineering feats that have transformed economies, connected communities, and enhanced the quality of life for millions.

A High-Speed Rail Revolution Beneath the Surface

Japan’s Shinkansen (bullet train) system is one of the most ambitious and successful underground rail projects in history. With large sections of the network passing through tunnels that slice through mountain ranges and congested urban areas, Japan has set the gold standard for high-speed rail tunneling.

The Seikan Tunnel (53.85 km) stands as a testament to Japanese engineering ingenuity. Linking Honshu and Hokkaido, it remains one of the world’s longest and deepest undersea tunnels. Excavated under extraordinary water pressure, in challenging geology, and in an earthquake-prone zone, this tunnel was more than an infrastructure project—it was a declaration that Japan’s engineers could master even the harshest underground conditions.

The upcoming Chuo Shinkansen Maglev, involving vast deep-underground tunnel networks, represents the future of high-speed travel, once again proving Japan’s ability to take on the most ambitious tunneling challenges.

Mastering the Depths: The Tokyo Bay Aqua-Line

One of the most daring underwater tunnel projects ever attempted, the Tokyo Bay Aqua-Line is a stunning blend of engineering mastery and environmental harmony. With 9.6 km of tunnel stretching under the bay, it dramatically reduces travel time across the region, exemplifying Japan’s expertise in undersea tunnel construction.

Overcoming some of the most hostile underwater conditions, including seismic risks and extreme water pressures, this tunnel set global precedents for safety and ventilation. Today, it stands as a model for other nations tackling similar engineering challenges.

A Leader in Underground Transportation Hubs

Japan has pioneered highly complex underground transportation hubs, integrating multiple transit systems in dense urban areas with unparalleled efficiency. The country has mastered the art of creating seamlessly connected multi-level underground networks, minimizing surface congestion while enhancing accessibility.

• Tokyo Station’s underground city is a prime example, housing high-speed rail platforms, metro lines, and vast pedestrian tunnels beneath one of the busiest rail hubs in the world.

• Osaka’s Umeda Underground Complex integrates rail, shopping, and business infrastructure across multiple levels, demonstrating advanced underground spatial planning.

• Shinjuku Station’s underground labyrinth, the busiest transport hub globally, exemplifies Japan’s ability to engineer massive subterranean spaces while ensuring intuitive passenger flow and emergency preparedness.

These projects reflect Japan’s leadership in underground urban mobility, setting global benchmarks for efficiency, disaster resilience, and transit-oriented development.

Fire Suppression Systems: Pioneering Safety in Road Tunnels

Japan has been at the forefront of fire safety innovation in road tunnels, developing some of the most advanced fixed fire suppression systems in the world. Recognizing the devastating potential of tunnel fires, Japanese engineers have led global advancements in automatic water mist, foam-based suppression, and early detection systems, significantly improving response times and minimizing damage.

Fire safety developments in Japan’s road tunnels, such as the Kan-Etsu Tunnel and Yamate Tunnel, have set benchmarks in tunnel resilience. Research into fire suppression effectiveness in confined spaces has informed global best practices, influencing ITA working groups and international road tunnel safety standards.

These innovations have dramatically improved survival rates in tunnel fire scenarios and have been adopted in major projects worldwide, reinforcing Japan’s leadership in underground fire engineering.

Advanced Underground Flood Mitigation Systems

Japan is also a world leader in underground flood prevention, having developed some of the most advanced tunnel-based flood mitigation solutions.

• The Metropolitan Area Outer Underground Discharge Channel, the world’s largest underground flood control system, protects Tokyo from catastrophic river overflows using colossal underground reservoirs and tunnels.

• The Fukagawa Underground Drainage System, a network of underground channels, reduces urban flooding by redirecting excess stormwater beneath the city.

• Multi-purpose underground spaces in Osaka and Tokyo are engineered for dual use—serving as transportation or commercial areas while doubling as emergency flood protection systems when needed.

These systems showcase Japan’s mastery of integrating flood resilience into underground infrastructure, ensuring urban safety while optimizing subterranean space.

TBM Innovation: Machines Built for the Impossible

Japan has revolutionized Tunnel Boring Machine (TBM) technology, with cutting-edge innovations that have made it possible to excavate tunnels under the most extreme geological conditions.

Japanese TBM manufacturers, including Hitachi Zosen, Mitsubishi Heavy Industries, and Kawasaki, have developed world-class machines designed for complex underground environments. The introduction of Variable Density TBMs and Multi-Mode TBMs—capable of adjusting to different soil conditions mid-operation—has changed the game in tunnel construction.

Japan’s mega TBMs, some of the largest in the world, have been instrumental in constructing massive underground projects, including multi-level urban road tunnels and ultra-deep high-speed rail tunnels.

Global Leadership in ITA Working Groups and Committees

Japan’s contributions to the International Tunnelling and Underground Space Association (ITA) have been instrumental in shaping global best practices. Japan has been a key voice in:

• Fire safety innovations, setting standards that have saved lives in underground spaces worldwide.

• Soft ground tunneling expertise, ensuring safer underground expansion in congested urban environments.

• Seismic-resilient tunnel design, providing critical insights for countries with high earthquake risks.

• Sustainable underground development, leading research on energy-efficient tunneling solutions.

Japan’s leadership and collaboration within ITA working groups have had a profound impact on global tunneling standards, ensuring that underground infrastructure remains at the forefront of safety, efficiency, and sustainability.

A Legacy of Excellence, A Future of Innovation

As we reflect on 50 years of Japanese underground engineering brilliance, we do not just celebrate structures of concrete and steel—we celebrate a nation’s vision, resilience, and unwavering pursuit of excellence. Japan’s tunnels are not just passages beneath the earth; they are monuments to human ingenuity, perseverance, and ambition.

On behalf of the International Tunnelling and Underground Space Association, I extend my deepest congratulations to Japan’s engineers, tunneling professionals, researchers, and policymakers who have shaped the industry. Your contributions have inspired the world and will continue to define the next frontier of underground infrastructure.

The future is underground, and Japan will undoubtedly remain a guiding light in that journey.