Underground masterpieces

By Carsten Paulun
Tunnels are more than mere passageways – they embody the art of engineering and creativity. From the roaring traffic in road tunnels to the silent tracks in railroad tunnels, from pioneering ship tunnels to secret escape routes for underground rescue missions – they all tell tales of progress and of overcoming obstacles.
© Statens vegvesen/Vianova/Baezeni
The highest-altitude tunnel
Underground masterpieces© https://mysterioustibet.com/

On the majestic elevations of the Tibetan Plateau, the Fenghuoshan Tunnel stretches as an architectural masterpiece and miracle of engineering. While it’s only 1,336 meters (4,383 feet) long, it’s located on an impressive 4,905 meters (16,093 feet) above sea level, which makes it the highest-altitude tunnel in the world. It’s part of the Qinhai-Tibet Railway the Lhasa Line of which that was inaugurated in 2006 connects the People’s Republic of China with autonomous Tibet.

Its construction in the dry and low-oxygen air that gets down to – 40 degrees called for innovative methods. They included the integration of an oxygen system into the construction site during the project, which also humified the air to curb the above-average development of dust. This enabled the tunnel excavation speed to be more than doubled from an initial two to three meters (6.6 to 9.8 feet) per day to five to eight meters (16.4 to 26.2 feet). The winds sweeping through the tunnel, occasionally knocking the workers off their feet, posed another problem. The English meaning of fenghuoshan is “wind volcano” for good reason.

Oxygen is still an important issue in today’s operation of the line. To protect passengers from mountain sickness, the trains of the Lhasa Line, like airliners, are equipped with a general oxygen system. Should the system prove to be inadequate every seat has an individual oxygen supply unit.

The Lhasa Line is not non-controversial. Its critics say that the line increases China’s control of the autonomous region of Tibet, promotes immigration from China, and thus dilutes Tibet’s culture.

The longest tunnels

© Hannes Ortlieb (Wikimedia)

Some of the structures in the realm of tunnels truly stand out as giants. Perched on the top of these underground masterpieces is the Gotthard Base Tunnel that has been stunning the world with its impressive length of 57 kilometers (35.4 miles) ever since its inauguration in 2016. This tunnel not only cuts through the Swiss Alps in the direction of Italy but also symbolizes the potential of the modern art of engineering.

Hardly less impressive is the Seikan railroad tunnel in Japan. Opened in 1988, with its length of 53.8 kilometers (33.5 miles) it connects the islands of Honshu and Hokkaido under the sea. In Europe, the Channel Tunnel, inaugurated in 1994, with its length of 50.5 kilometers (31.4 miles) serves as a subsea connection between France and the United Kingdom. The Yulhyeon railroad tunnel in South Korea, inaugurated in 2016, extends across 50.3 kilometers (31.3 miles) and via a high-speed railroad connects the cities of Mokpo and Gwangju.

Like the Gotthard Base Tunnel and parts of the Channel Tunnel, the underground section in Korea was built by means of the so-called new Austrian tunneling method (NATM). This construction method that was developed in the 1950s includes the surrounding part of the mountain as a co-supporting element in the construction while considering geological and rock-mechanical basics. NATM significantly reduces construction costs. As a result, it soon became the preferred tunneling method and has since seen continuous further development.


A masterpiece whose construction is expected to continue until 2032 is the Brenner Tunnel that by penetrating the Alps is intended to accelerate European rail transportation. The targeted track length is 64 kilometers (40 miles). With connecting, supply, and rescue tunnels, the system will even be 230 kilometers (143 miles) long. Half of the way through the rock is supposed to be cleared by blasting and the other half by drilling. The anticipated excavation of 21 million cubic meters (742 million cubic feet) of rock would suffice to fill an Olympic competition pool with a length of 420 kilometers (261 miles). Estimated costs of the mega project: ten billion euros.

Underground masterpieces© Kecko
The oldest tunnel
Underground masterpieces© Moawiyah Ibrahim

Hidden in the barren hills of Khirbet ez-Zeiraqoun (Jordan) is a fascinating secret: one of the oldest human-made tunnel systems in the world. Archeological discoveries suggest that these ancient tunnels were carved into the rock more than 4,000 years ago. They bear witness to an amazing art of engineering at a time when tools mostly consisted of stone.

According to historic records, these tunnels with a depth of up to 100 meters (328 feet) had a clear purpose: They ensured water supply. The academic world is still racking its brains wondering how the people that built it managed to keep the tunnel system from collapsing – three entrances, one staircase, and tunnels with a length of 200 meters (656 feet) still exist today.

The discovery of Khirbet ez-Zeiraqoun reminds us that the deepest secrets of human history are often hidden underground. These human-made tunnels are not only architectural masterpieces but also windows to a bygone world.

The deepest tunnel

© Privat

The Ryfylke Tunnel, Norway’s newest engineering masterpiece, stands out as the deepest tunnel in the world: It’s located 292 meters (958 feet) below sea level. The 14.4 kilometer (8.9 miles) long subsea tunnel (another world record) was opened to road traffic in 2019. The tunnel is part of Norway’s National Road 13 and runs underneath the Horgefjord between the city of Stavanger and the community of Strand in Rogaland. It replaces two ferries.

Despite its deep location the Ryfylke Tunnel is regarded as one of the world’s safest tunnels which is mainly due to its two tubes and a real-time radar monitoring system. In case of fire, people can escape into the other tube through cross headings existing every 250 meters (820 feet). In addition, the fan system can extract smoke in the direction of travel. To access its underground location, the tunnel has a 7 % gradient, which equates to the maximum permissible limit in road tunnel construction.

Before the project started, the construction terrain was surveyed and analyzed with computers. The data gained in that way also controlled the tunnel drilling machines that penetrated the rock. The largely automated processes ensured that the construction time of roughly six years remained equally reasonable as the construction costs equating to 720 million euros.

A feature that’s equally sensible and attractive is the tunnel’s LED lighting system that’s connected to sensors at the exits and so can adjust itself to the outdoor light. That improves the users’ ability to get used to the change in lighting conditions when entering and exiting the tunnel. In addition, the lighting concept serves to make the boring 15- to 20-minute trip through the tunnel more pleasant and attractive. Half-way into the tunnel, a domed drive-through hall featuring an exciting lighting concept as well has been incorporated for that purpose.

By the way, the Ryfylke Tunnel is not going to keep its record very much longer. Not far from it, Boknafjord Tunnel to be opened in 2029 is under construction. It’s going to be 27 kilometers (16.8 miles) long and run down to 392 meters (1,286 feet) below sea level, making it the world’s longest and deepest underwater road tunnel.

Underground masterpieces© T. Holme (Wikimedia)
Tunnels for ships
  • Canal du Midi with the Tunnel du Malpas, the oldest canal tunnel in the world
    Canal du Midi with the Tunnel du Malpas, the oldest canal tunnel in the world © VNF, Victor Tonelli
  • Planned Stad Ship Tunnel in Norway
    Planned Stad Ship Tunnel in Norway © Kystverket / Norwegian Coastal Administration
  • Length: 1.7 kilometers, width: 36 meters, height: 37 meters
    Length: 1.7 kilometers, width: 36 meters, height: 37 meters © Kystverket / Norwegian Coastal Administration

Tunnels for pedestrians, automobiles, and trains are part of our daily mobility life. But tunnels for ships? Even for them, appropriate structures can be found on our planet, such as the Tunnel du Malpas in France. It was built as far back as in 1679 in just eight days which, according to various sources, makes it the oldest canal tunnel in the world. On a length of roughly 165 meters (541 feet), its tube cuts through a hill between the Hérault River and the Canal du Midi.

France is also home to the world’s longest canal tunnel (7.1 kilometers/4.4 miles). The Rove Tunnel, though, has been closed since its collapse in 1963. Two canal tunnels with a length of more than one kilometer (0.6 miles) exist in the United Kingdom as well. All these tunnels have been designed for flat and slim ships.

The Stad Ship Tunnel in Norway is supposed to have clearly larger dimensions. With a length of 1.7 kilometers (1.1 miles), a height of 37 meters (121 feet), and a width of 36 meters (118 feet), this tunnel is supposed to enable circumnavigation of the dangerous Vestkapp with its up to 30-meter/100 feet-high waves and significantly reduce travel time. According to the Norwegian Coastal Administration, 81 percent of today’s ship traffic around the Vestkap will be able to use the tunnel, even the legendary Hurtigruten cruise ships. However, the start of the construction project with costs running into billions of kroner keeps being postponed. The technical effort entailed by tunneling through the hard gneiss rock is massive. A mixed drill and blast process has been proposed. Due to inadequate local roads, all the material required for the project must be delivered by ships. In addition, during the construction stage, the tunnel must be kept free of water by a rock wall to be constructed or possibly by cofferdams.

The cult tunnel

© Tama66 (Pixabay)

The St. Pauli Elbtunnel, just a few steps away from the Reeperbahn, Hamburg’s most notorious party district, is a special piece of Hamburg history. That’s not only due to its design: Ship container-sized elevators on the north and south banks of the Elbe River take tunnel users down to the two tubes traversing the river. 4,400 workers built the 426 meter (1,398 feet) long tunnel between 1907 and 1911 using the shield tunneling method with which the ingress of water into the construction section was prevented by means of compressed air.

The tunnel became necessary to transport the 25,000 port and 20,000 shipyard workers that were living in quarters on the north bank quickly to the port facilities south of the Elbe River. After it was opened, up to 19 million people per year were using this underground Elbe crossing. The user statistics not only reflect the high demand for this unique connection but also the important role that the St. Pauli Elbtunnel played in urban life.

With its construction time of only four years, the St. Pauli Elbtunnel was regarded as a pioneering feat back then. Its characteristic domed buildings and cast-iron elevators are not only architectural masterpieces but also symbols of Hamburg’s industrial progress. Passage of the Elbtunnel was free for pedestrians and bicycle riders and still is today.
However, the St. Pauli Elbtunnel has a problem: It’s located in too flat a position. Originally, three meters (9.8 feet) of the Elbe riverbed and mud separated it from the Elbe’s water.

When the Elbe River was deepened in 1981/82 this blanket was reduced to one meter (3.3 feet) and the tunnel protected with a ferroconcrete structure. Since then, more than a water depth of 10.6 meters (34,8 feet) for ships navigating the river is no longer possible – consequently, cruise ships such as the Queen Mary 2 (10.3 meters / 33.8 feet of draft) can make for the cruise ship terminal at the HafenCity only in high-tide conditions. For today’s giant container ships with a draft of 16 meters (52,5 feet) and more, Hamburg has enlarged the Waltershofer ports located in front of the St. Pauli Elbtunnel.

Underground masterpieces© 2857440 (Pixabay)
The most breathtaking tunnel
Underground masterpieces
Not for the faint-hearted: a dizzying ride on the Guoliang Tunnel Road

In the remote mountains of the Chinese province of Henan there used to be no reliable and fast connection between the village of Guoliang and its surroundings. But nobody cared about that except for the residents. That’s why in 1972 Shen Mingxin, the village’s mayor, decided to create the connection to civilization himself. He recruited 13 men to help him build the Guoliang Tunnel Road. The men worked their way through the hard mountain rock with the simplest of tools. During the work on the tunnel road several fatal accidents are said to have occurred.

But that’s not the only reason why the Guoliang Tunnel Road regularly appears on the lists of the world’s top ten most dangerous roads. Due to its steep slopes, numerous narrow corners, and lack of guard rails, traveling the tunnel road triggers feelings of fear. Even the slightest driving mistake can have dire consequences, although there’s no evidence of any vehicle ever having plunged off the road. Plus, the risk potential seems to attract rather than deter people. The thrill and the breathtaking views attract hundreds of thousands of tourists to the Guoliang Tunnel Road every year.

Despite the hazards the Guoliang Tunnel Road is an impressive example of human courage and determination. The road stands as a monument for the collaboration of the villagers who with the simplest of tools and great tenacity created this unique connection to their community.

The escape tunnel
Underground masterpieces
Commemoration of Tunnel 57 on Bernauer Strasse© N-Lange.de

In the dark days of the Cold War, Berlin became the symbolic front line between East and West. Following the erection of the Wall, as many as 70 escape tunnels were dug. The most famous one of them is Tunnel 57. Unlike conventional tunnels, this one did not represent progress of technology but the human yearning for freedom.

Between April and October 1964, 35 West Berlin escape helpers dug a 145-meter-/476-foot-long and 12-meter-/40-foot-deep tunnel from Bernauer Straße 97 in the western part of the city to a toilet house in the yard of Strelitzer Straße 55 in East Berlin. One of the helpers was the subsequent astronaut Reinhard Furrer. Their aim was to take people from the oppressed East into the free West.

Tunnel 57 was not only a physical gateway but also a symbol of resistance and overcoming of political boundaries. The construction of this tunnel was driven by the unshakeable desire for freedom and solidarity. Its existence reminds us that sometimes the simplest technologies are the most powerful expressions of human determination.

Tunnel 57 was one of three tunnels on Bernauer Straße through which people from East Berlin managed to escape. Tunnel 57 received its name from the number of people that were able to escape through it on October 3 and 4, 1964 before agents from the GDR’s Ministry for State Security (Stasi) discovered the system. The original plan had been for 120 people to escape.

The module tunnel

© Femern A/S

A bold project has been attracting Europe’s attention: the Fehmarn Belt Tunnel that’s to traverse the Baltic Sea between Germany and Denmark is under construction. With an impressive length of 18 kilometers (11.2 miles), this immersed tunnel will not only create an important road and rail connection between Fehmarn and the Danish island of Lolland but also go down in history as one of the longest underwater architectural projects. The Fehmarn Belt Tunnel is supposed to reduce the travel time of motor vehicles compared to ferry transportation from 45 to 10 minutes and the train travel time between Hamburg and Copenhagen from 5 to 2.5 hours.

The construction method of the immersed tunnel with which prefabricated tunnel segments are lowered to the bottom of the sea where they’ll subsequently be connected is an innovative technology. However, the engineers are faced with significant challenges, starting with ensuring the stability of the ocean floor to minimizing environmental impacts. Following its completion in 2029, the Fehmarn Belt Tunnel is supposed to be used daily by up to 10,000 passenger cars and 1,800 trucks and buses, and 111 trains, thus becoming one of the central elements of the European north-south transportation network.

Underground masterpieces
Visualisation of the portal and ramp to the tunnel© Femern A/S
Underground masterpieces
The German construction site on the island of Fehmarn. At Puttgarden, works on the German portal are ongoing. The construction of two of the three bridges required for the new alignment of B 207 (E47) and the railway line is being prepared© Femern A/S
Underground masterpieces
Visualisation of the immersion and connection of tunnel elements© Femern A/S
The tunnel city
Underground masterpieces© Anadolu Agency

Extending underneath the dusty plains of the Turkish town of Midyat is a fascinating underground labyrinth revealing a forgotten world. This underground city, whose origins date all the way to 200 A.D., served as a refuge for Christians protecting them against the Romans.

The underground complex of Midyat stretches across several levels and is home to residential areas, storage facilities, and even churches. Between 60,000 and 70,000 people are supposed to have lived here, according to archeological estimates.
The alleys and rooms of the underground city bear witness to a unique art of building that made it possible to create a livable environment amidst the rock.

Mysterious and almost forgotten, the underground city of Midyat today is deemed to be a historic heritage. Preserving and opening it to visitors enables us to investigate a world in which people adapted their way of life to the challenges of the times. Hence Midyat’s underground city not only remains an impressive archeological relic but also a window to the creative solutions of past generations for the protection and preservation of their habitats.

The floating tunnel

© Statens vegvesen

For upgrading European route 39 between Kristiansand in the south and Trondheim in the north, Norway is planning an ambitious project. By 2050, a little more than 100 bridges and 40 tunnels will have to be built for that purpose. One of those crossings concerns the Sognefjord, Europe’s deepest fjord (1,308 meters / 4,291 feet). Besides two bridge solutions, a unique tunnel is being discussed.

Because, due to the depth, the tunnel cannot be built on the ocean floor, engineers are thinking about building a floating tunnel with a length of 3,700 meters (2.3 miles) 20 meters (66 feet) below the water surface. As a result, cruise ships and freight vessels can continue to navigate the Sognefjord. The two tunnel tubes are supposed to be tethered to pontons. Besides passenger cars and trucks, pedestrians and cyclists are supposed to be able to use the Sognefjord Tunnel.

The then deepest and longest road tunnel in the world will be created as part of the E39 upgrade as well.

Underground masterpieces© Statens vegvesen
The most impressive natural tunnel systems
Underground masterpieces
The largest cave chamber in the world in terms of area: the Sarawak Chamber with a total length of 380 km© yusnizam (iStock)

Not only humans can build tunnels as nature has had this capacity for clearly longer and – admittedly – in more impressive ways. The tunnels of nature are called caves and the Jenolan caves in Australia with an age of 340 million years are deemed to be the oldest ones. The record of the longest cave is currently held by the Mammoth Caves in Kentucky (USA). To date, more than 600 kilometers (373 miles) of underground pathways have been mapped there. The second spot with a length of 311 kilometers belongs to the Sistema Sac Actun on the Yucatán Peninsula in Mexico. It’s also the longest underwater cave in the world. Georgia is home to the deepest cave in the world. The Veryovkina Cave extends from the entrance at 2,285 meters (7,497 feet) above sea level down to 2,223 meters (7,257 feet). Deemed to be the largest cave chamber in terms of area is the Sarawak Chamber that belongs to the massive Mulu system (total length of 380 km / 236 miles) on the Indonesian island of Borneo. Arguably, the Sơn-Đoòng cave system features the most impressive underground world. Two huge windows, at least 150 individual caves with lakes, rivers, and a jungle of its own as well as the world’s largest cave passage (250 m (820 ft) high, 15 m (50 ft) wide, and 9 km (5.6 mi) long) form perfect backdrops for photos.

Specialty warehouse for tunnel boring machines

Modern tunnel construction uses tunnel boring machines some of which have mammoth dimensions. Machines with a drill head diameter of up to 20 meters (66 feet) require powerful and reliable rolling bearing systems. The motion technology company Schaeffler offers such specialty products. The main bearing’s tasks include retaining the rotating drill head of the machine, absorbing the enormous feed forces, and supporting the massive tilting moments. Due to the variety of rock formations, the operating conditions, and hence the loads acting on the main bearings weighing up to 30 metric tons (33 short tons) constantly change.

That’s why after several months of service, tunnel boring machines are rebuilt in a complex process and components such as the bearings replaced. Because the lead time for a new, specially-made bearing is up to two years, refurbishing provides a highly attractive alternative. Refurbishing jobs done by the specialists at Schaeffler Industrial Remanufacturing Services AG & Co. KG in Wuppertal save up to 90 percent time, 60 percent costs, and up to 90 percent CO2 emissions.

Underground masterpieces