The Kerch Tunnel – possibilities and opportunities
Despite the political decisions leaded to the construction of the Kerch Strait Bridge, connecting the Crimean Peninsula with the mainland territory of Russia, the possibility to construct the tunnel under the Black Sea is still being widely discussed in the professional community.
Regardless of its importance and its scale, the experts still openly criticize the weak points of the project:
- The fairway’s narrowing,
- Limitations for the ship size,
- Weak protection from the military treats and terrorists acts,
- The difficult maintenance process when the weather conditions are not favourable.
Vladimir Markov, deputy director of Lenmetrogiprotrans, the St Petersburg based design institute known for their planning of the local metro systems and many objects across the country, commented the projects for UndergroundExpert.
The Kerch Strait Bridge connects The Kerch and The Taman’ peninsulas through the island Tuzla and Tuzla spit. Its total length is 23 km, the height – 40 metres. The structure designed with the railway and the road. The Bridge will have 4 lines for the vehicles, with the designed speed for them is 120 km per hour, and 2 rail lines for the trains. The road junction at the Taman’ side will also serve the port there. Also the bridge will be the part of the ring road in the area, the part of which goes along the Black Sea shore.
Why the bridge?
Vladimir Markov reminds that traditionally in Russia the construction of the tunnels is believed to be expensive, dangerous and labour-consuming task.
However, worldwide the tunneling develops rapidly for the obvious reason: the territory on the surface is too valuable not to preserve it by transferring engineering infrastructure and transport underground. In Russia, the territory is not such a valuable asset due to the size of the country and this issue is not very well regarded. The Government sticks to the traditional solutions and the state contractor usually considers underground options for the construction of engineering structures only in case other ways are technically impossible.
The construction specialists involved into tunneling form a small group whose abilities stay mostly unknown for the authorities. As was a case with the Kerch Bridge, simply no one at the state level promoted the idea of the underwater tunnel, while the idea to build the bridge initially sounded as a political statement.
Pro and Contra
According to Vladimir Markov, the construction of the tunnel meanwhile is the best possible solution. Here is why:
The bridge span has the significant length (23 km), and it brings along some restrictions.
- The long span structures’ supports will narrow the existing maritime channel, also the bridge suggests restriction of the height of the passing ships.
- The climate conditions are severe in this area with the frequent storm weathers the safety of the maintenance will become problematic.
- The bridge consists of the large long-span metal structures which require corrosion proofing, also some technical treatment is needed on a regular basis
- The bridge is vulnerable in face of terroristic acts and military treats.
Why the bridge is a bad thing and the tunnel is a good one?
It does not take a lot of explosions to eliminate the bridge, while the tunnel is more resilient to the mechanical damage. The tunnel won’t be too long, the road tunnel according to one of the possible designs was about 1.5-2 km, and the rail tunnel could be 3-4 km long. The width of the channel could stay the same and the ships would not be limited by their height.
Possible versions of the tunnel
From its inception, the idea of the tunnel construction developed in different technical varieties – from simple to exquisite. For example, it was suggested to construct a large-diameter double-track tunnel including the rail lines and roads. The option to build two tunnels (road and rail) with the contraflow. There were also suggestions to build 4 tunnels with obvious ordering and 3 tunnels (two one-rail tunnels and double-track road tunnel).
First option: The tunneling with the large-diameter TBM at the great depth. The tunnel with the diameter of the tunnels 19 metres may comprise the rails and the sections for the vehicles as well as the communication equipment. From Vladimir Markov’s perspective, this is slightly utopic idea and should be not taken seriously. And Russia does not produce the TBM suitable for the task at the moment.
The machine with the customized characteristics might be bought from abroad, like the TBM with 10.3 diameter, purchased by Metrostroy from Herrenknecht AG for the construction of the double-track tunnel for St Petersburg’ s metro. At the moment the order of such a unique machine for the construction in Crimea might be difficult. Geotechnical conditions at the construction site of the new station the Herrenknecht TBM works at is similar to the Kerch area and it proves that the TBM should be specially equipped.
Second option: The construction of the rail tunnels at the depth with the regular TBM (which may be manufactured in Russia). This idea is realistic, as the tunnel with such measurements may comprise the rail transportation. The depth required for this option provides favourable geological conditions. The length of the underground part of the tunnels would have reached 22 km.
«This is quite conventional option, not bad, although has its peculiarity: the necessity of the transportation of the motor vehicles with the piggyback service – at the railway platforms. It is hardly a problem, considering the experience of the Eurostar tunnel under the English Channel», – Markov comments.
Third option: The construction of the tunnel at the shallow depth with cut-and-cover method. According to Markov it is the easiest way. The similar solution worked for the road tunnel under the Gulf of Finland in St Petersburg, the tunnel is a part of the Flood Prevention Facility Complex.
«In our view, with this option being calculated, presented solution is the best from the point of technology. We suggest to construct the almost clone of the St Petersburg’s tunnel.
In this case, the tunnel would not be too long: 1.5-2 km – the road tunnel and about 3-4 km – the rail tunnel. The section of the route could run along the existing mound and the part along the low bridge. So this version has both the bridge and the tunnel. But the bridge could be smaller», – explains Vladimir Markov.
There is a dam at the Eastern side very close to the island of Tuzla, which in its turn is very close to the maritime channel. At the Western side there are shallows (2-3 metres deep waters), allowing constructing temporary dam.
From St Petersburg’s dam designers
Suggested by Lenmetrogiprotrans design includes the section of the route along the mound, underwater tunnel and the short bridge. It is simple from the technical point and efficient in terms of economy.
- The width of the tunnel, comprising both road and rails – 30 м.
- The height – 5.5 м.
- Maximum depth – 25 м.
«The construction techniques could be similar to the techniques used for the shallow underground metro stations. In particular, the metro station Novokrestovskaya, which is being constructed in the similar geological conditions.
It does not require special equipment. Supposedly the diaphragm wall might be constructed and then the jet-grouting method applied. The construction works could be performed at all sections simultaneously making the construction period being 3-4 years quite possible. In terms of design, it would be railroad tunnel and road tunnel in one rectangular cross-section», – comments Vladimir Markov.
This designing solution from St Petersburg designers can be described in short as «tunnel between the dam and the bridge». At the transition section the road will run parallel to the portal of the road tunnel and descend into the tunnel later. The only challenge to be encountered with is in the necessity of the temporal (for the period of the construction of the underflow tunnel) shift of the maritime canal’s bed closer to its historical place and back. The same procedure was successfully conducted during the construction of the C1 section of the Flood Prevention Facilities Complex in St Petersburg. As for the cost and the time period of construction – these parameters are comparable to the current figures, or, perhaps, even less.
To be continued?
The most expensive way is the construction of a paired rail and road tunnels. Of course, the construction of four deep laid tunnels would cost even more, than the bridge. The decision made had obviously the political connotation as well. And what will happen now to the project of the tunnel? At the first sight, it is abandoned, but maybe the final judgement should be reserved in this case.
Three years ago the Ministry for Transportation of the Republic of Crimea assigned the authorities of Kerch the task of founding the place for a new port. The railroad carries more passenger trains at present, but may not provide sufficient source for the cargo transfers. For that very reason it is possible that the construction of the special crossing would be needed eventually. According to experts, the private investment sector keeps the interest for the transport tunnel under the Kerch Strait.
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