Seikan tunnel

As I wrote in the previous post, on 18th July after having lunch at a restaurant in Aomori railway station, hubby and I went to the platform where we took a train named ‘Hakucho’ for traveling to Hakodate city in Hokkaido prefecture. The train travelled through an undersea tunnel named Seikan tunnel that has been acting as a main artery that connects the islands of Honshu and Hokkaido. We wished to do sightseeing inside Seikan tunnel and so we bought train tickets that included Tappi undersea railway station tour and Seikan Tunnel Memorial Hall tour course.

Hakucho train at Aomori railway station

Seikan tunnel is a 53.85 km railway tunnel with a 23.3 kilometer long portion under the seabed, and is the longest undersea tunnel in the world. The tunnel travels beneath the Tsugaru Strait linking Aomori prefecture of Honshu and the neighboring island of Hokkaido. The tunnel contains a rail line and is part of the Kaikyo Line of Hokkaido Railway Company. The tunnel connects Aomori city and Hakodate city in just two and a half hours, and was named by combining the two characters and pronunciations of ‘ao (sei)’ of Aomori city and ‘hako (kan)’ of Hakodate city. The tunnel runs at a maximum depth of 140 meters from the sea water level and 100 meters further down from the seabed. Seikan tunnel actually consists of multiple tunnels. A two-track main tunnel for trains travelling, a smaller service tunnel next to it, and an even smaller pilot tunnel below the other two that was dug the first. Today, the service and pilot tunnels are used for maintenance and evacuations. There are other tunnels such as inclined and vertical shafts to connect to the ground.

Seikan tunnel schematic

Typical tunnel cross section model showing main tunnel, service tunnel, and pilot tunnel

Construction of Seikan tunnel began in 1964 and was completed in 1988. About 168,000 tons of steel and 850,000 tons of cement were required for the construction. It was impossible to bore the tunnel because of the unpredictable nature of the surrounding rock, so 6.3 million cubic meters of earth were blasted out. The amount of explosives used for blasting was approximately 2,900 tons. Total construction cost was about 690 billion yen. The tunnel boasts some interesting engineering features. The rails inside Seikan tunnel are welded together, which makes them the longest rails on earth. The super long rail is 52.57 km in length. Furthermore, the tunnel has triple slab track type rail, which is capable of running Shinkansen bullet trains along with regular trains in future. The tunnel remains one of the most formidable engineering feats of the 20th century.

There are two undersea stations inside the tunnel. One is Tappi Kaitei station on the Aomori side which is 135 meters undersea, and the other is Yoshioka Kaitei station on the Hokkaido side which is 149.5 meters undersea. They are both located just under the coastal line. In these two station buildings tour courses have been established with reference displays of the Tsugaru Strait and the Seikan tunnel. However, since 2005 the guided tours for the Yoshioka undersea station are closed due to the ongoing Shinkansen construction that is predicted to start operation by 2015.

The Hakucho train departed from Aomori station at 11.56 am and arrived at Tappi Kaitei undersea station at 12.44 pm. Tappi Kaitei station is one of the two emergency stations for the tunnel and is located on the Kaikyo Line in Sotogahama in Aomori prefecture. Tappi Kaitei is very infrequently serviced by JR trains but is connected by an underground cable car to the surface. As we neared the train station, it was announced that to leave the train we had to go to car no. 2. This is because Tappi Kaitei station is only one car length long. There were about 15 other people heading for the undersea tour. The tour was for about 3.5 hours and there was a railway tour guide to help us.

Hakucho train at Tappi Kaitei undersea station

Walk from Main tunnel to the service tunnel

After moving to the service pit tunnel, the tour guide collected our baggage and put it inside a locker. The guide told us that the walk to the underground cable car would take about 30 minutes. We enjoyed walking in the tunnel and also saw some of the tools used during the construction of the tunnel. At the beginning of our walk in the service pit, we saw an inspector ride by in a bicycle. It was really wonderful to walk inside the tunnel.

An inspector riding a bicycle in the service tunnel

A board indicating Tappi Kaitei railway station

Service tunnel

There was a pleasant breeze blowing inside the tunnel. By sending 3,800 square meters of wind from both the Yoshioka inclined shaft and the Tappi inclined shaft every minute, a one-meter wind continually blows toward the exits allowing for continual ventilation. Throughout the year the environment underground is maintained at a temperature of 20 degrees and humidity is set at 80-90%. After about ten minutes of walk, the guide told us that we had reached a spot where outside the tunnel there was sea water on one side while ground on the other! It was indeed a thrilling experience. The tunnel was fully made of concrete and sometimes mystery tunnels branched off into the darkness.

Spot where outside the tunnel there was sea water on one side and ground on the other

Service tunnel

Branched off tunnel where we were not allowed to enter

Drainage is a big problem in the tunnel as water drips from everywhere here. The amount of sea water soaking the walls of the tunnel that is drained and pumped back to the surface is about 20 tons a minute. In fact, as we walked we felt that we heard the sound of water as if we were in a forest. This sound actually comes from the drain. In addition, we saw that there were rails embedded in the floor of the tunnel. The guide told us that during the construction of the tunnel, this particular tunnel was one of the access tunnels bored to transport people as well as spoil away from it. One of the two rails has been concreted up, while the other has been left to assist in drainage.

Hubby feeling the wetness of cemented walls of the tunnel

Sea water seeping into the tunnel

Two rails embedded in the floor of the service tunnel

It was an amazing experience to walk inside the tunnel at about 140 meters under sea level. Hubby compiled a short video of our walk in the service pit of the Seikan tunnel.

Video of walk inside service pit of Seikan tunnel

Soon we reached a place inside the tunnel called Tappi Kaitei world. It was a medium sized gallery that included many displays of tools and photos related to the construction of the tunnel. Here our guide stopped and explained in details about the map and route of the tunnel.

Panel explaining the tunnel design at Tappi Kaitei world

Display of some of the tools used during construction of the tunnel

Me standing at the lowest point inside the tunnel

After walking for some more time, we passed through a large airlock arrangement and reached the Driftway exhibition (Taikenkodo in Japanese) corner. The tunnel was very dimly lit here. The construction site of the tunnel was recreated, and the machinery and tools that were used to excavate were on display.

People passing through a large airlock arrangement

Driftway exhibition display of a photo regarding the construction of the tunnel

Display of a few tools at the Driftway exhibition

Display of shotcreting technique

Display of rock drilling machine inside the tunnel

Display of heavy machinery equipment used for the construction of the tunnel

Display of heavy machinery equipment used for the construction of the tunnel

The engine could pull heavy loads of gear and people through the service tunnel

Above photo taken from another angle

After seeing the exhibition, our walk inside the tunnel was over and we reached the cable car underground station named ‘Taikenkodo eki’ that hauled our group up to the ground surface. The name of the railway line is ‘Seikan Tunnel Tappi Shako-sen (inclined line), which is a funicular line operated by Seikan tunnel museum. The cable car named ‘Mogura’ uses the Tappi inclined shaft to connect the underground Driftway exhibition point to the Seikan Tunnel Memorial Hall museum above ground. The elevation of the Tappi shaft is 778 meters and there are 2247 steps in the shaft staircase. It took about five minutes to reach the railway station named ‘Seikan tunnel kinenkan eki’ at the ground level. After reaching the museum station, a massive door closed behind us and we were allowed to climb out of the cable car to enter the Seikan Tunnel Memorial Hall museum.

Underground cable car station named Taikenkodo eki

Photo taken from the back of cable car while travelling up the inclined shaft

We were allowed to come out of the cable car after the massive steel door closed

Mogura cable car at the station named Seikan tunnel kinenkan eki

Inside the museum building, the tour guide took all of us to a meeting room and strictly instructed us to be back there by 3.25 pm. After that we were on our own for a while. The museum exhibited the history of Seikan tunnel from the conception of the idea through the actual construction, completion, and operation of the tunnel by means of audio, video, panels, and three dimensional models. It was very interesting to know the various steps involved in the skillful building of the tunnel.

A huge three dimensional display of Seikan tunnel location and position

Me standing in front of the three dimensional display of Seikan tunnel

Panel explaining the details of Seikan tunnel

Another panel giving details of the tunnel

Three dimensional display of the actual size of the tunnel

Hubby standing next to the display of tunnel

Hubby reading the history of the tunnel

Hubby reading the technical details of the tunnel

Hubby seeing the model of the tunnel and its surrounding area

Hubby seeing the display of cutter head of a tunnel boring machine

Me posing next to a model of a worker using equipment for construction of the tunnel

Me standing next to the model of a worker using equipment for designing the tunnel

After seeing the museum, we went outside the museum to have a look at the ground and the surroundings. The museum building had many circular shaped rooms which looked very beautiful from outside. There were several pieces of old equipments on display outside the museum. In addition, we could clearly see the base of Seikan tunnel in the mountain to our left. Unfortunately it was a cold, rainy, and a very windy day, and so after a few minutes we headed back inside the museum building.

Museum building from outside

Two tunnel boring machines used for the excavation on display outside the museum

Some of the pieces of old equipment on display outside the museum

Base of Seikan tunnel on Honshu side (Seikan tunnel Honshu gata kichi Tappi)

We had lunch at the cafe of the museum. After that we returned to the meeting room of the museum and waited for our guide. At 3.30 pm, the guide took all of us to the cable car station for our descent back down to the tunnel. Inside the tunnel, we walked back to the Tappi Kaitei station. We again enjoyed our walk in the tunnel and saw many small details that we missed during our onward walk. On reaching Tappi Kaitei station area, we took our baggage from the locker, and then waited for the Hakucho train to arrive. The train departed the station at 4.18 pm and reached Hakodate railway station in Hokkaido at 5.33 pm.

Walking back in the tunnel towards Tappi Kaitei station

Walking back in the tunnel towards Tappi Kaitei station

Hubby standing next to the board of Tappi Kaitei railway station

Main tunnel showing two railway tracks; photo taken from Tappi Kaitei platform

Straight across to the other platform

Me at Hakodate railway station platform

Hakucho train at Hakodate railway station platform

Hubby and I really loved the tour of Seikan tunnel. It was an amazingly wonderful experience to see one of the greatest engineering feats of the 20th century. At Hakodate railway station, we kept our baggage in a locker located inside the station itself and then did sightseeing at Mt. Hakodate about which I will write in the next post.