With the increase in the depth and width of water barriers, the cost of constructing underwater tunnels increases sharply and problems arise associated with the lowering and underwater joining of tunnel sections. In this regard, a number of countries are working on various conceptual and technological solutions for the construction of “floating” tunnels.
Located entirely in the water, shallow from the surface (depending on navigation conditions up to 30-35 m), such tunnels are held by a system of vertical or inclined cables, fixed to the bottom of the water barrier, or fixed to pontoons (see Fig. 1.1, d, e) .
At the same time, the length of the tunnel passage is significantly reduced, there is no need to open underwater pits and backfill sections, the connection of the underwater part with the coastal sections is simplified and the cost of construction is reduced. Such tunnels can be built up to 30 km long at water depths of up to 500 m or more.
In addition to the usual permanent and temporary loads, the structures of “floating” tunnels are subject to loads caused by fluctuations in water temperature, currents, ebbs and flows, changes in water density, compression waves from passing ships, the likelihood of a collision between ships above the tunnel, loss of buoyancy, damage to the fastening system, etc. .
Norway has developed a program for the construction of “floating” tunnels through deep fiords (water depth up to 600 m). Individual reinforced concrete sections ranging from 300 to 500 m in length are kept afloat by guy ropes attached to the tunnel structure and in anchor arrays at the bottom of the fiord.
An example is the project for the construction of a “floating” tunnel near the city of Stavanger at a depth of 25 m from the surface of the water in a fjord 155 m deep (Fig. 5.22 and 5.23).
Rice. 5.22.
Of the various options for “floating” tunnels - supported on coastal abutments (with a short length), on intermediate supports, anchored into the bottom of the strait (Fig. 5.24, a) or suspended from pontoons (Fig. 5.24, b) - A Kvaerner-developed steel structure consisting of lowering sections, secured by cables to cylindrical pontoons, was chosen. It can be assembled away from the tunnel route and then delivered to it afloat.
It is planned to build a tunnel through Hogsfjord on the southwestern coast of the country. The width of the fiord at the intersection is 1400, depth - 150 m. The construction of a bridge or a tunnel buried in the bottom in this place is fraught with significant difficulties. Tunnel sections of circular cross-section made of prestressed reinforced concrete with a diameter of 9.5 m will be immersed to a depth of 15-20 m below the water level and anchored with cable guys to the bottom (Fig. 5.25).
Rice. 5.23. Options for the cross section and fastening of the “floating” tunnel near Stavanger in Norway: 1 - tunnel; 2 - water level in the bay; 3 - bottom of the bay; 4 - cable stays
Based on six years of comprehensive design and research work, the construction of a “floating” tunnel under Eidfjord has also been proposed. The width of the fjord is 1270 m, the depth of the water is 400-500 m. The tunnel of prestressed reinforced concrete sections with a diameter of 9.5 m is designed at a depth of 15 m from the water surface and is secured with cables to the bottom, and horizontal braces to the shore anchor devices. A variant has been developed for fastening the tunnel with floating paired pontoons anchored to the bottom. Each pontoon is attached to 24 gravity anchors by means of double 44mm diameter steel cables passed through looped outlets at the top of the anchors.
A three-section “floating” tunnel is designed for the Eiden fjord with a width of 1240 m and a depth of 450 m.
The largest “floating” tunnel (model of the “Archimedes Bridge”) for passing combined road and rail traffic between the mainland and the island of Sicily was designed in Italy through the Strait of Messina. Several tunnel options have been proposed, differing in dimensions, anchoring method, etc.
Rice. 5.24. Options (a, b) of floating tunnels: 1 - tunnel; 2 - anchor guys; 3 - pontoons
According to one of the options, a tunnel with a total length of 3.25 km includes lowering sections made of prestressed reinforced concrete, made in the form of three conjugate circular tunnels with an outer diameter of 12.3 m. The side tunnels are intended for two-lane road traffic, and the central one for double-track railway traffic (Fig. 5.26 ).
With a strait depth of 100-130 m, the “floating” tunnel is planned to be located at a depth of 40 m from the surface of the water for the purpose of unhindered passage of ships. The position of the tunnel sections, which have positive buoyancy, is strictly fixed by a system of paired cables anchored in reinforced concrete masses laid along the bottom of the strait.
It is planned to install three sections of prestressed reinforced concrete on the 2.05 km long underwater section. The sections are equipped with fairings on the sides to reduce the force impact of the water flow. The guy rope system is designed for a tunnel lifting force of 96 thousand kN (300 kN per 1 m of tunnel length) and for horizontal sea current pressures.
Rice. 5.25. Schemes (a, b) of “floating” underwater tunnels under Hogsfjord in Norway (project): 1 - sections of the tunnel; 2 - pontoon; 3 - anchor plate; 4 - cable stays
The main cables are attached to the tunnel structure every 10 m and anchored into reinforced concrete masses at an angle of 60° to the horizontal. Another group of cables for perception of horizontal pressure is attached to the tunnel at an angle of 45°. The tension force of each cable is 1260 kN, the weight of the anchor concrete mass is about 300 tons.
The design of the “floating” tunnel includes emergency compartments that prevent the tunnel from rising by filling them with water (the valves are automatically activated) in the event of a break in one of the cables.
Rice. 5.26. Cross-section of the “floating” tunnel under the Strait of Messina (project): 1 - compartment for cars; 2 - ballast weight; 3 - compartment for railway trains; 4 - cable stays; 5 - anchors; 6 - fairings; 7 - water level; 8 - bottom of the strait
According to another version of the project, three separate tunnels are provided: one for double-track railway traffic with a length of 5.4 km and two for two-lane road traffic with a length of 6 and a diameter of 15.5 km. The tunnels will be secured at a depth of 47.75 m from the water surface using guy ropes.
In Japan, projects have been developed for the construction of “floating” tunnels between the islands of Honshu and Hokkaido, under Uchiura Bay, as well as between Kasan and Kobe airports through the bay in Osaka. Of greatest interest is the project of a two-tier underwater tunnel between the islands of Honshu and Hokkaido through Fuka Bay. The upper tier is intended for two-lane road traffic, and the lower tier is for double-track railway traffic. In an underwater area at depth
The “floating” tunnel is held 20 m from the water surface by guy ropes. To counteract vibrations of the tunnel structure during the movement of trains and cars, as well as from sea waves, fin-type stabilizers are additionally provided.
In Switzerland, three options have been developed for the construction of a transport crossing of the lake from north to south: a bridge, a tunnel constructed using a closed method, and a “floating” tunnel. The latter turned out to be preferable. Ten tunnel sections, consisting of two coaxially located steel pipes with a length of 100, an outer diameter of 12 and an inner diameter of 11 m with concrete filling between them, will be held at a depth of 14 m from the water surface by a system of cables located every 50 m at an angle of 45° to the horizon.
There are also project proposals for the construction of “floating” tunnels across the Strait of Gibraltar and the English Channel, under the Great Lakes in the USA and Canada.
The tunnel was completed in 1988 and stretches for 54 kilometers, reaching a depth of 240 meters, but its underwater part (23.3 kilometers) is dwarfed by the Channel Tunnel (Chunnel) connecting the UK and France. It was completed in 1994, and the underwater part of the tunnel ranges from 38.6 to 50 kilometers, but dives only 75 meters deep.
However, both tunnels are dwarfed by the $3.3 billion Marmaray Tunnel. Its 13.2-kilometer railway track (including 1,400 meters of seabed along the Bosphorus Strait) connects the Asian and European sides of Istanbul, thereby making it the first railway tunnel to connect two continents.
What is so wonderful about a one and a half kilometer tunnel compared to the many kilometers long Seikan and Channel? The difference is in the approaches. While Marmaray's predecessors blasted and pierced solid rock, the Turkish tunnel was assembled piece by piece in a trench at the bottom of the Bosphorus, making it the longest and deepest submersible tunnel ever created. Engineers chose this solution, using pre-assembled sections connected by thick, flexible, rubber-steel plates to better combat regional seismic activity.
For some time, cultural and historical artifacts from old Istanbul that were found on the seabed slowed down the excavation process of the Marmaray Tunnel, so the 3.6 km Øresund Tunnel, connecting Sweden and Denmark, remained the largest submersible tunnel. Contractors built it from 20 elements of 176 meters each, connected by smaller, 22-meter sections.
Between submersible tunnels like Marmaray and Öresund and ordinary ones like the Chunnel, there is much more. Let's delve a little deeper and look at another tunnel construction method that has been in use since the early 19th century.
Tunneling shield of unusual sizes
The oldest approach to constructing underwater tunnels without drainage is known as shield tunneling; engineers still use it today.
The shields solve a common but vexing problem: how to dig a long tunnel through soft ground, especially underwater, without the leading edge collapsing.
To get an idea of how the shield works, imagine a coffee cup with a pointed end that has several large holes in it. Now, holding the open end of the cup, push the soft soil through it and see how the dirt comes out through the holes. On the scale of a real shield, several people (mucker and sandhog) will stand inside the compartment and clean it of clay or dirt as it fills. Hydraulic jacks will gradually push the shield forward, and the crew will install metal support rings, marking the forward movement with them, and then make concrete or masonry on their basis.
To prevent water from seeping through the tunnel walls, the front of the tunnel or shield is sometimes subjected to compressed air pressure. Workers who can withstand only short periods in such conditions must go through one or more airlocks and take precautions against pressure-related illnesses.
The panels are still used today, especially when installing pipelines or water and sewer pipes. Although this method is quite labor-intensive, it costs only a fraction of what it costs to use its cousins, tunnel boring machines (TBMs).
The TBM is a multi-story monster of destruction capable of chewing through solid rock. At the front of its cutting head is a giant wheel with rock-cutting discs and buckets for unloading waste stone onto a conveyor belt. In some large projects, like the Chunnel, individual machines started at opposite ends and drilled to the end point, using complex navigation techniques to ensure they didn't end up missing the target.
Drilling through solid rock creates mostly self-supporting tunnels, and the TBM moves forward quickly and relentlessly (during the construction of the Chunnel, machines sometimes moved as much as 76 meters per day). Cons: The TBM breaks more often than a used penny and doesn't work well with broken or twisted rocks - so sometimes you can't move as quickly as engineers would like.
Luckily, TBMs and backboards aren't the only players on the field.
Let him drown!
Building masonry and supporting rings and at the same time biting into soft earth or hard rock is, of course, no picnic, but only Moses is capable of trying to hold the sea under water. Fortunately, thanks to the invention of the American engineer W. J. Wilgus, the sunken or submerged tube tunnel (ITT, PTT), we do not need to try to repeat the feat of the prophet.
PTTs do not penetrate stone or soil; they are put together from parts. Wilgus tested this technology during the construction of the Detroit River Railroad connecting Detroit and Windsor. The technology caught on, and more than 100 of these tunnels were built in the 20th century.
To make each tunnel segment, workers pour together 30,000 tons of steel and concrete—enough to build a 10-story building—into a massive mold and then let it sit for a month. The molds include the floor, walls and ceiling of the tunnel and are initially closed at the ends, making them watertight when transported at sea. The forms are transported by submersible pontoons, large vessels that resemble a cross between a gantry crane and a pontoon boat.
By descending a pre-dug chute, each part of the tunnel fills enough to sink on its own. The crane slowly lowers the section into position, and divers guide it using GPS. As each new section connects to its neighbor, they are connected by dense rubber that inflates and contracts. Afterwards, the crew removes the sealing partition and pumps out the remaining water. Once the entire tunnel is built, it will be filled in, possibly with broken rock.
Immersion pipes can be built deeper than in other cases because the equipment does not need to use compressed air to keep the water outboard. Teams can work longer. In addition, submersible structures can be cast into any shape, unlike a TBM tunnel, which follows the shape of the machine's path. However, since submersible tunnels constitute only a portion of the seabed or riverbed, different tunnel construction mechanisms and techniques are required for land entrances and exits. In underwater tunneling, as in life, all means are good.
If there are large rivers, sea straits or bays along the highway route, it may be necessary to construct underwater tunnels, which in some cases have technical and economic advantages over bridge crossings. Underwater tunnels do not violate the conditions of navigation and everyday life of the water barrier. Low banks of the watercourse, which increase the cost of the bridge crossing due to the need to ensure under-bridge dimensions, are favorable for the construction of an underwater tunnel.
Approaches to bridges, especially in urban areas, disrupt the architectural ensemble and may, in some cases, require the demolition of buildings and structures.
The choice between a bridge and a tunnel crossing a water barrier is made on the basis of a technical and economic comparison of options, taking into account both construction and operating costs.
In some cases, when crossing large water obstacles, it is advisable to construct combined tunnel-bridge crossings, consisting of a low-level bridge and an underwater tunnel on a navigable section.
Typically, underwater tunnels are built under the bottom of a watercourse, leaving a protective soil roof of at least 3-6 m (Fig. 3.4, a).
Rice. 3.4.
1 - underwater section; 2 - ramp section; 3 - dam;
4 - winding sections; 5 - supports
When constructing underwater tunnels in conditions of significant water depth (more than 30 m), tunnels located on artificial dams arranged along the bottom of a watercourse (reservoir), tunnel-bridges and floating tunnels can be used. The design of a tunnel on dams consists of separate ready-made elements - tunnel sections, which are lowered from the surface of the water or moved from the banks along the axis of the tunnel along rails laid along artificial dams, and then joined together (Fig. 3.4, b). The construction of such tunnels significantly reduces the length of the underwater passage, but this requires a significant amount of earthwork for the construction of dams.
An underwater tunnel-bridge is a combined structure in the form of a tunnel of separate sections, supported on supports like pavements (Fig. 3.4, c). Such structures can be constructed at the intersection of very deep watercourses, and the depth of the tunnel is determined by the conditions of navigation.
Unlike bridge tunnels, floating tunnels are held at the required depth from the surface of the water by guy ropes anchored to the bottom.
Approaches to the tunnel - ramp sections - are constructed in an open excavation with a lining in the form of an open structure made of monolithic or precast reinforced concrete, consisting of a tray and side walls of variable height, reinforcing the slopes of the excavation. The length of the ramp depends on topographical, geotechnical conditions and economic factors. In some cases, closed-type ramps of a seamless design are installed.
On March 13, 1988, the Seikan Tunnel, the world's longest underwater railway tunnel, was opened in Japan. Today we decided to talk about it and other most remarkable underwater tunnels that tourists can visit.
The longest
While Chinese scientists are working on the project of the next record holder - an underwater tunnel with a length of 123 km - the longest operating railway corridor on the planet remains the Japanese Seikan. It took 42 years and more than 3.6 billion dollars to implement the idea of connecting the two largest islands of the Land of the Rising Sun by the shortest route. The initial time and cost of constructing Seikan was increased either by weak soils, too much water pressure, or endless financial difficulties. And then on March 13, 1988, the Japanese press finally exploded with enthusiastic essays: the train, hidden in the depths of the tunnel in Honshu, rushed under the waters of the Sangar Strait and emerged like a float in Hokkaido. The “majestic spectacle” (as “Seikan” is translated from Japanese) reaches a length of 53.85 km, a little less than half of which is hidden in the underwater depths. The tunnel is equipped with protection from natural disasters and the force of the water element: ultra-sensitive sensors are installed inside that respond to the slightest vibrations of the earth, powerful pumps that pump out up to 16 tons of water per minute, and impressive shelters with sufficient reserves in case of disaster. Now Seikan is not as famous as it was 20 years ago, but is still a landmark in Japan.
The oldest
An interesting fact: the very first “underwater bridge” on the planet was supposed to connect the two banks of the Neva in St. Petersburg. But fate decreed otherwise. The royal customer Alexander I died before the talented architect Marc Brunel completed the project, and his heir Nicholas I was not interested in the technical innovation. The developer decided not to let the good things go to waste, and turned to another “advanced” monarch – Queen Victoria of England. Here he was luckier: the method he invented, which is still used in the construction of tunnels, was implemented to connect the two banks of the Thames. 50 thousand Londoners gathered to watch the opening of an underwater communication 459 meters long. By the standards of 1843, this was almost half of the capital's population! Although the tunnel never became a cargo tunnel due to a lack of funding, it was extremely popular: walking under the river seemed as incredible as being on the moon. The corridor turned into a city of entertainment: a shopping gallery and an underwater brothel appeared here, and the world's first underwater fair was held. After some time, the passage under the Thames was abandoned: for 145 years only wayfarers looked here. More recently, voices have been heard again in the oldest underwater tunnel in the world: London authorities are conducting walking tours through the historical dungeons.
Photo: usolt.livejournal.com
The most deep
The construction of a tunnel under the Bosphorus, which managed to connect Europe with Asia, was a long-standing Turkish dream that seemed like a fantasy. It took more than 150 years to realize the idea that the Ottoman Sultan Abdul Hamid had back in 1860. The opening of the Marmaray tunnel, which took place on October 29, 2013 and coincided with the National Day of Turkey, was not without incidents: electricity was cut off in Marmaray and passengers were forced to get out of the train stuck in the tunnel. The length of the communication, which unites three underground and 37 above-ground stations, 8 suburban and 4 interchange stations, reaches 13.6 kilometers, with 1,400 meters passing directly under the Bosphorus. The capacity of the double pipe, laid 60 meters below the bottom of the strait, is one and a half million passengers per day, and its safety system can withstand earthquakes of 9 points on the Richter scale. In addition to the undeniable economic benefits that solved the problem of congestion in Istanbul’s transport system, the construction of Marmaray brought another unexpected benefit. During the mega-construction, 40 thousand important archaeological finds were discovered, including a flotilla of 30 Byzantine ships, worthy of a place among World Heritage sites.
Photo: andrewgrantham.co.uk
Most entertaining
Until 1997, a distance of 15 kilometers, ridiculous by today’s standards, did not seem like just an annoying trifle to residents of the Japanese cities of Kisarazu and Kawasaki. Because the shortest distance between these points lay across Tokyo Bay, Kisarazu, which lies very close to ultra-modern Tokyo, resembled a rural outback. After all, to get there by car from the capital, you had to travel a hundred kilometers. Japanese engineers were faced with an extremely difficult task: building a bridge between different sides of Tokyo Bay would impede the movement of sea vessels, and building a tunnel was too problematic due to the instability of the seabed. The technical solution was ingenious: Aqualine was a very successful and safe combination of an underwater tunnel 9.6 km long and a bridge 4.4 km long. But it was not the sensitive smoke detectors installed every 25 meters, nor the latest anti-seismic technology that placed the Tokyo tunnel in this rating. On one of the two artificial islands through which Aqualine passes, there is an entire entertainment complex similar to a passenger liner. In addition to parking for 480 cars, there are restaurants, souvenir shops, recreation areas and observation decks.
The most famous
Everyone knows about the modern wonder of the world that connected Foggy Albion with the Fifth Republic: the Eurotunnel, opened under the English Channel in 1994, has become a symbol of the unification of Europe. The idea of creating a direct route from England to the mainland came to the minds of outstanding figures of all times: from scientists of the 13th century to the ambitious Napoleon, who dreamed of sending cavalry under the strait, carrying out ventilation through pipes reaching the surface. And only at the end of the 20th century “Europe finally joined Britain”: three tunnels (two for train traffic and one reserve) are connected into a single system by air vents and spare tunnels. In order to reduce the piston effect that occurs when high-speed trains move at speeds of up to 350 km/h, a ventilation system is laid over the tunnels, and refrigeration stations are installed at both ends, cooling the rails. Interesting fact: the British approached the construction of the 51-kilometer Eurotunnel with particular enthusiasm. They dug faster than the French and dug 15 km more. And they treated the land created during construction more romantically, creating the man-made Cape Shakespeare. The disadvantages of the Eurotunnel (for example, high tolls) are compensated by its undeniable advantage: it is the fastest and most interesting way to get from continental Europe to Britain.
Underwater tunnels can be used to create a permanent transport connection through a water obstacle (river, canal, lake, reservoir). They best meet the condition of ensuring uninterrupted traffic flow on both intersecting highways (land and water) and have the following advantages over bridges:
do not violate the domestic regime of the watercourse;
do not interfere with navigation, completely preserving the existing character of the water area;
protect vehicles from adverse atmospheric influences;
ensure uninterrupted and year-round traffic movement in the watercourse crossing area;
preserve the location of coastal structures and devices, minimize the number of buildings and structures subject to demolition on the approaches to the intersection;
practically do not disturb the architectural ensemble of the city.
A technical and economic comparison of a bridge and a tunnel crossing shows that an underwater tunnel has a higher construction cost, but the operating costs of maintaining bridges, especially low-water ones, are significantly higher than tunnels.
In general, underwater tunnels are most often used in the following topographical and geotechnical conditions:
a wide watercourse with flat, low, often built-up banks;
the bed of the watercourse is formed by a thickness of weak soils, extending to a fairly large depth; at their base lie stronger soils;
the movement of land or water transport at the intersection is characterized by high intensity and consistency throughout the day.
In addition, preference is given to the tunnel option in the presence of floods and powerful ice drifts occurring at high water levels, instability of the riverbed, as well as due to urban planning requirements.
Depending on the location relative to the bottom of the watercourse, they are distinguished (Fig. 2.72):
underwater tunnels, completely buried in the soil massif;
tunnels on dams or individual supports;
floating tunnels anchored by cables into the river bed.
Underwater dam tunnels, bridge tunnels and floating tunnels are effective in crossing deep water obstacles. When using them, the transition length is reduced and the operational performance of the route is improved.
The choice of location for an underwater tunnel within the city limits is determined by the nature of the layout and development of urban areas, topographical conditions of the area and construction method. Typically, they try to position the tunnel intersection perpendicular to the axis of the watercourse, which makes it possible to reduce the length of the structure and simplify its construction and operation. In conditions of densely built-up banks, it is possible to construct an oblique crossing of a water barrier.
The underwater tunnel can be located either on a straight or curved route. The curvature of the tunnel route is caused by the need to go around obstacles: erosion zones, islands, artificial underwater structures; or, conversely, the desire to approach the island to construct ventilation shafts or open additional faces.
The most typical, in addition to rectilinear ones, are the following options for the location of the underwater tunnel in plan:
To place the channel section on a straight line, within the coastal sections, the tunnel route is placed on curves (Fig. 2.73, a);
The approaching coastal sections of the underwater tunnel fall on different sides of the bend, so the axis of the tunnel in plan is located on the curve (Fig. 2.73, b);
Due to the mismatch of the axes of the underwater sections on both banks of the watercourse, the curved sections of the track are located near the water's edge, and the entire tunnel has an elongated S-shape in plan (Fig. 2.73, c);
To organize an intermediate construction site associated with a change in the construction method or, if necessary, the installation of a ventilation shaft, natural or artificial islands in the watercourse are used, which allows the tunnel route to bend in plan (Fig. 2.73, d).
In any case, it is necessary to comply with regulatory requirements for the elements of curved sections of the road and their mutual connection.
The longitudinal profile of the tunnel can be designed with a gable concave outline, with a flat lower dividing section, or, if the structure is of a significant length, the dividing section can be replaced by two longitudinal profile elements with slopes directed from the middle of the tunnel to the banks of the watercourse. In places where the slopes are planned to meet, if their algebraic difference is large, elements of transitional steepness are assigned to ensure compliance with the regulatory requirements for the longitudinal profile. In particularly long underwater tunnels, a multi-slope longitudinal profile can be designed, dictated by the bottom elevations along the tunnel route and the conditions for ensuring minimum burial depths.
When designing the longitudinal profile of an underwater tunnel, much attention is paid to the correct setting of the depth of the top of the tunnel relative to the bottom of a watercourse or reservoir, which is assigned depending on the construction method and soil properties.
If the underwater part is constructed using a shield method under compressed air, then, in order to avoid its breakthrough, the minimum depth relative to the line of possible erosion is determined depending on the properties of the soils composing the channel bed: 4-6 m in dense clayey soils, 8-10 m in weak ones non-cohesive soils. Reducing the thickness of the protective roof can be achieved by installing a protective clay mattress 2-3 m thick and 3-4 times the width of the tunnel along the bottom of the reservoir, directly above the structure.
When constructing the under-channel part using the method of lowering sections, the depth of the tunnel is set to be no less than: 2.5-3 m in weak, non-cohesive soils and 1.5-2 m in dense clayey soils.
They try to combine the places of fractures of the longitudinal profile with the joints of the sections. This facilitates the design of the sections themselves and the installation of a base for it.
A typical example is the 5.8 km long railway tunnel under San Francisco Bay (Fig. 2.75). The need to bypass earthquake-prone areas in the bay and the polygonal shape of the longitudinal profile led to the curvature of the longitudinal axis of the structure in the horizontal and vertical planes. As a result, out of 57 sections of the tunnel, 15 have a curved outline in plan and 4 in profile. The two sections are segments of a spiral, curved in both planes.
The cross-sectional shape of the under-channel part is determined by the excavation method and, in most cases, when using the shield method or the method of lowering sections, it has a circular or rectangular outline.
The depth of water above the tunnel must be sufficient for navigation.
To combat water appearing in an operating structure, a water intake is installed in the lowest place of the tunnel and a low-power pumping station is placed in it. It is used to remove relatively small volumes of water collecting in the closed part of the tunnel. High-performance drainage pumps are installed at the bottom of open ramps to intercept and remove rainwater. In addition, to prevent flooding of the underwater tunnel, various design solutions are provided (Fig. 2.76).
The underwater communication tunnel in Sveaborg (Finland), built in 1980, has a total length of
1265 m, cross-sectional area about 13 m2. The tunnel contains heat and water supply and electrical cables. A pump is installed at the lowest point to pump out drainage water.
In Norway, the world's first floating automobile tunnel with a diameter of 20 m and a length of 1440 m, anchored into the ground, was designed. The tunnel is expected to have a two-lane roadway, pedestrian and bicycle paths.
In 2001 in Moscow, as part of a transport interchange at the intersection of Volokolamsk Highway with st. Svoboda, a unique tunnel under the canal was put into operation. Moscow. The tunnel route consists of two sections: the first is about 160 m long, built as a single monolithic reinforced concrete structure without intermediate expansion joints. The second section, approximately 240 m long, consists of nine sections separated by intermediate expansion joints. In cross section, the tunnel is a two-section box with dimensions of 7.9x28.7 m, designed to carry five lanes of traffic (Fig. 2.80).
