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 a dwarf next to the Channel Tunnel or "tunnel" (Channel Tunnel, Chunnel) connecting the UK and France. It was completed in 1994, and the underwater part of the tunnel is between 38.6 and 50 kilometers long, but plunges only 75 meters deep.
However, both tunnels are dwarfed by the $3.3 billion Marmaray Tunnel, which . Its 13.2 km railway track (including 1,400 meters on the seabed of the Bosphorus) connects the Asian and European sides of Istanbul, making it the first railway tunnel to connect two continents.
What is so remarkable about a one and a half kilometer tunnel compared to the multi-kilometer Seikan and Channel? difference in approaches. While the predecessors of the Marmaray blasted and forced their way through hard 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 built. The engineers chose this solution, using pre-assembled sections connected by thick, flexible, rubber-steel plates to better deal with regional seismic activity.
For some time, cultural and historical artifacts from old Istanbul found on the seabed slowed down the excavation of the Marmaray tunnel, so the 3.6-kilometer 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 tunnels like the "Chunnel" there is a lot more. Let's go a little deeper and look at another tunneling method that has been in use since the early 19th century.
Tunneling shield of unusual size
The oldest approach to constructing underwater tunnels without diverting water is known as the tunneling shield; engineers use it to this day.
Shields solve a common but very annoying problem: how to dig a long tunnel through soft earth, especially underwater, without its leading edge collapsing.
To get an idea of how a 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, press the soft earth into it and see how the dirt comes out through the holes. At 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 up. Hydraulic jacks will gradually push the shield forward, and the crew will install metal support rings, marking forward progress with them, and then make concrete or masonry based on them.
In order to prevent water from seeping through the walls of the tunnel, the front of the tunnel or shield is sometimes subjected to compressed air pressure. Workers who can only endure short periods in such conditions must pass through one or more locks and take precautions against pressure related illnesses.
Shields are still used today, especially when installing pipelines or water and sewer pipes. And although this method is quite laborious, it costs only a small part of the cost of using its relatives - tunnel drilling machines (TBM).
The TBM is a multi-story monster of destruction that can gnaw through solid rock. In front of its cutting head is a giant wheel with rock cutting discs and buckets for unloading the waste stone onto a conveyor belt. In some large projects, like the Tunnel, individual machines would start from opposite ends and drill to the end point, using complex navigation techniques to ensure they didn't miss the mark.
Drilling through solid rock creates mostly self-supporting tunnels, and the TBM moves forward quickly and relentlessly (during the construction of the Chunnel tunnel, vehicles moved at times as much as 76 meters a day). Cons: TBM breaks more often than a used penny and doesn't work well with broken or twisted rock - so sometimes you can't move as fast as the engineers would like.
Luckily, TBMs and shields 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 can try to hold the sea under water. Fortunately, thanks to the invention of the American engineer W. J. Wilgus, the sunken or submersible tube tunnel (ITT, PTT), we do not need to try to repeat the feat of the prophet.
PTTs do not break through stone or soil; they come together from parts. Wilgus tested this technology while building a railroad on the Detroit River connecting Detroit and Windsor. The technology caught on and over 100 of these tunnels were built in the 20th century.
To make each segment of the tunnel, 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 brew 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.
Going down a pre-dug chute, each section of the tunnel fills up enough to sink on its own. The crane slowly lowers the section into position while divers guide it using GPS. As each new section connects to its neighbor, they are connected by a dense rubber that inflates and compresses. After the crew removes the sealing partition and pumps out the remaining water. Once the entire tunnel is complete, it will be filled in, possibly with broken rock.
The construction of dip pipes can be done deeper than in other cases, because the technician does not need to use compressed air to keep the water overboard. Teams can work longer. In addition, submersible structures can be cast in any shape, unlike the TBM tunnel, which follows the shape of the path of the machine. However, since submersible tunnels are only part of the seabed or riverbed, land-based entrances and exits require different tunneling mechanisms and techniques. In underwater tunneling, as in life, all means are good.
Norway is a country of fjords - narrow, winding and deep sea bays with rocky shores that cut deep into the land. Their length is several times greater than their width, and the banks are formed by rocks up to 1 km high.
Despite the extraordinary beauty of nature, this complicates the transport crossing. Conventional tunnels at the bottom of the sea are practically impossible in many places due to the depth of the fjords, and bridges are difficult to build due to the rugged relief of the coast and steep cliffs.
Then the idea arose to create car tunnels floating in the water column. The first crossings may appear between the cities of Kristiansand and Trondheim by 2035. If the project is implemented, the road along the sea will take motorists 10 hours instead of 21 hours due to the refusal of ferry crossings.
The project is a hybrid of a tunnel and a bridge hanging below the surface of the water, but high above the bottom, which can be very deep (the Sognefjord reaches 1.3 km).
Two tunnels - one in each direction - will be located at a depth of about 30 meters. Each of them will be a rigid pipe 26 km long. They will be connected to each other by passages every 250 meters in case of evacuation.
The slope of tunnels should not exceed 5%. The pipes will be collected on land, after which they will be loaded into the sea. Several ballast tanks will be filled with water so that they sink to the desired depth. The force of the air inside the pipes and lifting them up will be equal to the weight of the tanks with ballast, lowering the pipes down. Due to this, it will be possible to avoid buoyancy.
From above, the pipes will be held by cables fixed on top of the pontoons, and heavy anchors will attach them to the bottom. In this way, specialists will achieve complete immobility of the tunnels, ensuring a safe ride.
However, for motorists, tunnels will still be classified as objects of increased danger. Any accident that would be considered minor on a normal road can even lead to disaster in a tunnel inside the mountain. And in the Norwegian tunnels over each square meter of the road there will be 30,000 liters of water.
The depth of the tunnel - 30 meters - was chosen in order not to interfere with navigation.
Despite such an unconventional solution, driving in an underwater pipe will not differ in any way from driving through a conventional tunnel. In Norway, 1150 transport tunnels have been built, 35 of which pass under water, so that the inhabitants of this country will not be out of the ordinary to move along floating underwater crossings. For example, in 2013, the longest underwater tunnel Karmey was opened there. Its length is almost 9 km.
3. Terms and definitions
In this standard, the following terms are used with their respective definitions:
3.1accident in the tunnel: a dangerous traffic accident that poses a threat to the life and health of people and leads to damage or destruction of vehicles, elements of building structures or equipment, as well as traffic disruption in the tunnel.
3.2road tunnel: urban underground (or underwater) structure, passing through a soil massif or under a water obstacle, for the passage of vehicles in order to decouple traffic at different levels (at intersections, junctions or forks of highways), increase the capacity of highways, overcome high-rise or contour obstacles, access to major urban centers, etc.
3.3height dimension of the transport zone of the tunnel: the shortest distance from the top of the pavement to structural elements or equipment located at the top of the tunnel, allowing or restricting the passage of a vehicle.
3.4clearance of structures and equipment: the limiting outline of free space in a plane perpendicular to the longitudinal axis of the carriageway, inside which no elements of a structure or equipment or devices located in it should enter.
3.5dam: construction in the form of an embankment of earth materials of trapezoidal section for regulating water flows, blocking snow avalanches, etc.; the upper bed of the dam is in some cases used for laying transport communications.
3.6frost resistance grade of concrete: number of cycles of alternate freezing and thawing in water, which withstand samples made and tested for frost resistance in accordance with the requirements of current state standards
3.7metal insulation: covering of steel sheets combined with the reinforcing cage of the lining..
3.8loading dock: a construction-launching structure, which, like the construction dock, has a gate from the side of the water area, but the bottom of the loading dock is made two-stage: its upper part is above the water area level, and in the deep-water part, the water level with the gate open corresponds to the water area level. Construction sites in the loading dock are located in the upper part of the pool or in adjacent chambers located at the same level as the upper stage and separated from it by special gates. The upper stage of the loading dock is filled with pumps, and drained by gravity. Liquid docks, like construction docks, are equipped with cranes and equipment for loading and withdrawing sections of the tunnel.
3.9lining: load-bearing structure enclosing an underground working and forming the inner surface of an underground structure.
3.10loweringunderground structures: for various purposes, the structures of which are erected on the earth's surface, and then lowered to the design depth. There are drop structures: drop wells, drop (submersible) support, drop sections of underwater tunnels, drop tunnels-caissons.
3.11underwater tunnel: a tunnel constructed under a water obstacle for the passage of vehicles and pedestrians, the laying of engineering communications, etc.
3.12pontoon: a floating craft that serves to place technological equipment on it.
3.13tunnel portal: a structure for holding the slopes of the approach cuts and an architecturally designed entrance or exit from the tunnel,
3.14tunnel building: auxiliary underground structure adjacent to the main tunnel or connected to it by an underpass
3.15roadway of the tunnel: tunnel element intended for the movement of vehicles
3.16closed face mode: shield driving mode, in which the development of the soil of the face is combined with the effect on its surface of an active weight (earth and/or foam soil, bentonite suspension, compressed air), which balances the current total pressure of the soil in the face and hydrostatic pressure.
3.17open face mode: driving mode, in which driving is carried out in stable soils. With water inflow in the face and water inflow along the length of the tunnel, local drainage is used.
3.18ramp: a structure that serves to interface the closed part of the tunnel with the surface of the earth.
3.19service pass: a strip allocated at the tunnel wall with some elevation above the level of the carriageway, intended for the passage of service personnel through the tunnel.
3.20sunscreen: a building structure installed over a section of the road adjacent to the entrance portal to exclude direct sunlight or reduce the penetration of scattered daylight onto the carriageway of this section and is intended for brightness adaptation of the driver when entering a motor transport tunnel.
3.21reinforced concrete structures: reinforced concrete structures, including steel sheet and shaped elements other than reinforcing steel, working together with reinforced concrete elements
3.22sections of the underwater tunnel (lowering): elements from which the tunnel is built by the lowering method.
3.23dry dock: an open area or a pit on the bank of a watercourse, fenced on all sides by bulk dams, the height of which should be sufficient so that after the flooding of the dock, the lowering tunnel sections can be afloat with maximum draft.
3.24TPMK: tunnel-boring mechanized complex (TPMK)
3.25bridge tunnel: a kind of underwater tunnel located in the water column on bridge-type supports.
3.26transport zone: the main part of the tunnel, which serves for the passage of vehicles or part of a complex underground structure with a roadway located in it, other elements of building structures, as well as operational equipment necessary for using the tunnel as a transport structure.
3.27tunnel route: a line representing the position of the axis of the tunnel in space.
3.28deformation seam: a structural element to ensure the possibility of moving parts of the structure without force action of the lining elements on each other under the influence of their sediment, temperature changes, concrete shrinkage and prevention of cracking.
4. General provisions
4.1 Underwater transport tunnels during their entire service life must meet the requirements of safety and uninterrupted movement of vehicles, reliability and durability of building structures, convenience and the lowest cost of their maintenance during operation, and environmental requirements. Tunnels should provide a socio-economic effect due to a decrease in overruns of vehicles, a decrease in traffic accidents, and a general improvement in transport services for the population.
Underwater tunnels should be attributed to the I increased level of responsibility of structures, failures of which can lead to severe economic, social and environmental consequences
The adopted technical solutions, designs and materials must ensure the service life of tunnel linings of at least 100 years. The overhaul periods of building structures should be at least 50 years.
4.2 The main space-planning and design and technological solutions - the location of tunnels and tunnel structures in terms of and longitudinal profile, the length of sections constructed in an open, lowering and closed way, types of lining, placement of the roadway, ventilation ducts and cable collectors along the tunnel section, - should be determined at the "Design documentation" stage based on the results of feasibility comparisons of various options and taking into account the category of the road on which the tunnel is being designed.
4.3 As part of the tunnels, if necessary, a complex of operational and technical premises for electrical, ventilation, drainage installations, water supply and other devices should be provided. If possible, they should be combined into operational and technical blocks.
4.4 Instruments and equipment placed in tunnels must have the necessary degree of protection from the effects of aggressive factors in the air environment of tunnels, high humidity, temperature changes, as well as from damage during mechanized washing of wall structures or attempts to deliberately damage them.
The laying of utilities, with the exception of distribution networks, suitable for equipment installed directly in the areas of the traffic areas of the tunnels should be provided, as a rule, in technical rooms, ensuring a high degree of their protection, especially in emergency situations.
4.5 The service life of the main operational devices installed in the tunnels and on the approaches to it must be at least 10 years.
4.6 When designing tunnels, in addition to this standard, the requirements of the relevant chapters of SNiP and state standards of the Russian Federation, departmental regulatory documents, regulatory documents of state administration and supervision bodies and other regulatory documents on construction design should be taken into account.
5. Initial data and engineering surveys for design
5.1 Initial data
5.1.1 Initial data are formed in accordance with SP 122.13330. The initial data for the design of tunnels are:
Geophysical research;
Field studies of soils;
6.2.6 The passage of main heating networks, water and gas pipelines through the tunnel structure is not allowed.
6.2.7 The largest longitudinal slopes of ramp sections must comply with the requirements for open sections.
6.2.8 The longitudinal slope of the carriageway from the drainage conditions should be taken at least 0.03, with the exception of sections of vertical curves.
The maximum longitudinal slopes in road tunnels should not exceed 40 ‰, and in difficult topographic and engineering-geological conditions with a tunnel length of up to 500 m - 60 ‰.
6.2.9 The conjugation of adjacent elements of the longitudinal profile of tunnels should be performed by fitting convex or concave vertical curves, the smallest radii of which can be taken as for open sections of streets and highways.
UNDERWATER TUNNEL (a. underwater tunnel; n. Unterwasserstollen, Unterwassertunnel; f. tunnel sous-marin; and. tunel submarino) - designed to overcome a water obstacle in order to pass vehicles and pedestrians, lay utilities, etc. Underwater tunnels, in contrast from bridges do not violate the regime of the watercourse, do not impede navigation, protect vehicles or communications from adverse atmospheric influences, and when located in the city, they minimally disturb the architectural ensemble. The advantages of underwater tunnels in comparison with bridges increase to a large extent with gentle banks of the watercourse and with intensive navigation.
Depending on the location relative to the bottom of the watercourse (reservoir), there are underwater tunnels buried in the soil massif (Fig., a), tunnels on dams (Fig., b) or separate supports (tunnel-bridges) (Fig., c) and " floating "tunnels (Fig., d).
Tunnels on dams, bridge tunnels and "floating" tunnels are effective when crossing deep water barriers, because. at the same time, the length of the tunnel crossing is reduced and the operational performance of the route is improved.
The world's first underwater tunnel (900 m long, 4.9 m wide and 3.9 m high) was built in Babylon under the Euphrates River in 2180 BC. e. A large number of underwater tunnels for various purposes are operated in the world, among which transport tunnels predominate:, metro (table).
Underwater tunnels were built under the rivers Moskva, Neva, Kura on the lines of the Moscow, Leningrad and Tbilisi metros, road tunnels - under the canal. Moscow in Moscow, under the Sea Canal in Leningrad, etc. It is planned to build the largest underwater tunnels under the English Channel (52 km), the Strait of Gibraltar (32 km), the Gulf of Bothnia (22 km), the Bosphorus (12 km), the Strait of Messina and etc.
Underwater tunnels are located on a straight or curved track in plan, which is associated with the need to bypass areas of strong erosion, islands, artificial underwater structures, etc. 8-10 m in non-cohesive soils. With the method of lowering sections, the minimum laying depth in dense clay soils is 1.5-2 m, and in non-cohesive soils 2.5-3 meters. Curve radii in plan and profile, longitudinal slopes and dimensions of underwater tunnels are taken depending on the purpose of the tunnel and its location in accordance with the relevant standards. The width of underwater tunnels reaches 40 m or more, the height is 10 m (for example, in Antwerp).
The method of construction of underwater tunnels is determined by its length, cross-sectional dimensions, topographic, engineering-geological and hydrological conditions. Underwater tunnels are most often constructed using the shield method or the method of lowering sections. In some cases, mining or open methods are used, and in difficult engineering and geological conditions - tunneling under compressed air, lowering caissons, dewatering, grouting, artificial freezing or chemical fixation of soils. The structures of underwater tunnels constructed by the shield method are made in the form of circular tunnel linings made of cast-iron or steel tubing or reinforced concrete elements with internal waterproofing. With the mining method of work, linings of a vaulted outline of monolithic concrete or reinforced concrete are arranged. Lower sections of underwater tunnels can be of circular, binocular or rectangular cross-section made of reinforced concrete with external waterproofing. Underwater tunnels are equipped with artificial ventilation, lighting, drainage systems, as well as special devices that ensure the safe operation of the structure.
Underwater tunnels as transport tunnels and crossings are widely used in large cities to overcome navigable rivers, canals and bays. The main advantages of the construction of underwater tunnels in comparison with the bridge crossing of water barriers are as follows: the domestic regime of the watercourse is not disturbed, they do not interfere with navigation and the operation of existing coastal structures (piers, berths, etc.). Underwater tunnels have especially great advantages when large-tonnage vessels pass along a river or canal, which makes it necessary to have a large height and length of bridge spans, and, consequently, powerful supports, which in turn leads to a significant increase in the cost of a bridge crossing in in general.
The choice of tunnel or bridge options should be decided on the basis of taking into account the totality of factors - technical, operational and economic.
The construction of underwater tunnels is carried out as follows.
The main element of the underwater tunnel are the lower sections, which are mainly used in a circular or rectangular shape. Lower section of a circular section (Fig. 3, a) usually has a lining, including a steel shell, inside which is a reinforced concrete lining. The thickness of the lower section of the circular shape varies within 0.5-0.7 m.
Lower sections of rectangular shape are made of monolithic reinforced concrete. Depending on the throughput of the tunnel, the lower sections have a different number of compartments. They can be single-span and multi-span. On fig. 3 , b presents a single-span descent section adopted during the construction of the Kanonersky underwater tunnel under the Sea Canal in St. Petersburg. The tunnel is designed for two-lane road transport with a side passage for people 1 and a ventilation gallery 2. The length of each section is 75 m. The structure of the section is made of monolithic reinforced concrete with a thickness of 0.93 m. The mass of the section is about 8000 tons. External waterproofing 3 steel with a thickness of 6 mm, which is simultaneously used as a formwork for the construction of a reinforced concrete lining of the section. On fig. 3, in a section of the underwater tunnel "La Fontaine" in Montreal (Canada) across the St. Lawrence River is presented. The lower section has a rectangular shape with dimensions of 36.73x7.85 m and a length of 109.7 m. The mass of the section is 32,000 tons. The sections are made of monolithic reinforced concrete with prestressed reinforcement 1 , for which we used cables of 48 wires with a diameter of 7 mm and temporary strands 2. The cladding is waterproofed 3. The sections at the ends are equipped with temporary waterproof diaphragms, in which sluices with gates are provided to let people through and to control the tightness when joining the sections.
To accommodate the lower sections in the channel of the water barrier, a trench is arranged. The dimensions of the trench are determined by the main dimensions of the section. The width of the trenches along the bottom is 2-3 m and more than the width of the section, and the depth of the trench is not less than 0.5-0.7 m. Gravel or crushed stone preparation is laid at the base of the trenches.
The production of submersible sections is usually done in a dry dock or lock dock, which is located on the shore and in such a way that they can be used at the completion of construction as a ramp approach during the operation of the tunnel.
Figure 3. Sectional shapes of the descent sections of underwater tunnels
In the dock, depending on the required quantity, either all sections are made when the watercourse has a small width, or part of them as work progresses on the construction of an underwater tunnel.
After the sections are made, water is pumped into the docking lock to its level in the watercourse. Sections float and are towed afloat to the installation site. Before diving, a special pipe is installed on the sections to allow people to pass through it and supply materials, and sighting masts are also mounted, which control the position of the sections. Sections are immersed by filling special ballast tanks placed inside them with water. After immersion and installation of the section, it is joined using a special profile of a rubber cuff and a coupling device in the form of a jack. In the future, the joint is monolithic from the inside of the section. After installing all the submersible sections and checking the tightness of the joints, they are backfilled with fragmental materials to a height of 1.5-3 m.
