THE SEIKAN TUNNEL

Civil Engineering Consortium IIT Roorkee

5 min readNov 10, 2021

INTRODUCTION

Japan’s 53.85km Seikan railway tunnel passes beneath the Tsugaru Strait and connects the Aomori Prefecture on Honshu Island and the Hokkaido Island. With its track located 140m below the seabed, the Seikan tunnel is the world’s deepest and longest railway tunnel. Approximately 23.3km of the tunnel lies under the seabed, making it the world’s longest undersea tunnel.

HISTORY AND CONSTRUCTION TIMELINE

In 1954, a typhoon sank five ferry boats in Japan’s Tsugaru Strait and killed 1,430 people. In response to public outrage, the Japanese government searched for a safer way to cross the dangerous strait. With such unpredictable weather conditions, engineers agreed that a bridge would be too risky to build. A tunnel seemed a perfect solution. Ten years later, work began on what would be the longest and hardest underwater dig ever attempted.

The timeline of the construction of this tunnel goes as follows:

24 April 1946 — Geological surveying begins.

26 September 1954 — The train ferry Toya Maru sinks in the Tsugaru Strait

23 March 1964 -Japan Railway Construction Public Corporation is established..

28 September 1971 — Construction on the main tunnel begins.

27 January 1983 — Pilot tunnel breakthrough.

10 March 1985 — Main tunnel breakthrough.

13 March 1988 — The tunnel opens.

26 March 2016 — Shinkansen services commence operation through the tunnel, regular narrow gauge passenger services through the tunnel cease.

ENGINEERING SPECIFICATIONS

Type of Tunnel : Double Track Rail Tunnel

Track Length : 53.85 km (23.3 km undersea)

Track Gauge : Dual Gauge (1435 mm Standard Gauge for Shinkansen trains and 1067 mm Narrow Gauge for freight trains)

Engineers couldn’t use a tunnel boring machine(TBM) to carve the Seikan Tunnel because the rock and soil beneath the Tsugaru Strait was random and unpredictable. Instead, tunnel workers painstakingly drilled and blasted 33 miles through a major earthquake zone to link the main Japanese island of Honshu with the northern island of Hokkaido.

Three stories high and 800 feet below the sea, the main tunnel was designed to serve the Shinkansen, Japan’s high-speed bullet train.

Materials used during the construction of the Seikan Tunnel include more than 2,800 tons of explosives, and one hundred sixty-eight thousand tons of steel was used in the construction of the tunnel.

During construction in 1976, tunnel workers hit a patch of soft rock with disastrous results. Water gushed into the tunnel at a whopping rate of 80 tons per minute. It took more than two months to control the flood. Luckily, no lives were lost

ROLLING STOCK

Today, about 50 freight trains and 30 Shinkansen bullet trains pass through the tunnel every day, carrying more than two million tons of cargo each year. ED79 and EH500 class locomotives carry freight and offer overnight sleeping car services through the tunnel.

The Hayabusa Shinkansen series, a Japanese bullet train with a top speed of 199 miles per hour, has to slow down to 87 miles per hour in the tunnel to avoid disrupting the freight trains. At full speed, the wind pressure created when the two trains cross paths could cause the freight trains to spill their loads. Ways to manage this situation, and to raise the speed limit, are still being investigated.

SHAFTS OF THE TUNNEL

Vertical Shaft

These shafts are constructed vertically downwards. These shafts were used for elevators to haul workers, materials, and machinery. Now these shafts are used for circulating fresh air inside the tunnel.

Main Shaft

This is the main tunnel, in which the railway lines are placed. This shaft is constructed 7.85 meters high and 9.7 meters wide.

Pilot Drift Shaft

It was used as a supporting shaft for digging the main shaft and the construction shaft. Testing and research of the nature of the soil and sea water leakage were performed using this shaft. The digging operations were performed after all these inspections. Presently, this shaft is used for drainage and ventilation.

Construction Shaft

The construction shaft is built to the side of the main shaft. This shaft was used for connecting guide paths. It was very important because it enhanced the pace of digging by increasing the face. It was also used for transporting materials and machineries.

Inclined Shaft

Two main inclined shafts were constructed, first in Yoshioka and the second in Tappi. It was made inclined at an angle of 14 degrees to the side of sea bed, and it was mainly used for geological surveys. Rather, it was also used for transporting workers, materials, machinery, and the rocks and mud left due to the dig. Now, a cable car is used in this shaft to carry materials.

SEISMIC STUDIES

It was deduced in a study that when an earthquake took place in 1969(when one of the sloping galleries of the tunnel was under construction) the amplitude in the tunnel was only 20 % of the amplitude on the surface. This along with the fact that big earthquakes are not likely to occur in the zone of the tunnel led to the expert’s conclusion that the effects of such earthquakes in this tunnel will be relatively minor.
An earthquake took place in 1983 of magnitude 7.7 on Richter Scale, which did not cause any damage to the tunnel in spite of the tunnel being under construction at that time.

CONCLUSION

The Seikan Tunnel is one of the largest tunnels in the world. Most of the technologies used in its construction were applied for the first time, and now, these technologies are used worldwide. The process of inspection of this tunnel is unique, and the Seikan Tunnel is a lasting gift of engineering for Japan

Author : JATIN SINGH

REFERENCES

THE SEIKAN TUNNEL

Written by Civil Engineering Consortium IIT Roorkee