Due to the frequent shipping in places where underwater tunnels need to be built, the methods of digging the cover of the dike and pneumatic caisson will cause great interference to the water traffic. Therefore, for more than 50 years,1underwater tunnels have mostly been built by shield method and immersed tube method.
After 1950s, major technical keys such as submerged pipe joint and foundation treatment have been broken through one after another, which greatly simplified the construction technology, greatly improved the waterproof performance of the tunnel, and adopted a rectangular section that can accommodate more than four lanes.
Under certain conditions, immersed tube method has the advantages of shallow soil cover, short line, low cost of lighting and ventilation, low cost of engineering and operation, and good use effect. Therefore, since 1965, more than 20 underwater highway tunnels have been built all over the world, and most of them adopt immersed tube method.
Excavation and covering: drainage, deep pit excavation, construction and landfill. This method is the simplest, but the construction site is large and restricted by the surrounding buildings. This method is used in Dushu Lake Tunnel in Suzhou and Donghu Tunnel in Wuhan.
Shield method: the most commonly used and advanced method in tunnel construction. It started in Britain and Japan, with a history of 180 years. Its greatest advantage is that it is suitable for tunnel excavation in soft soil geology.
Freezing method: freeze the soil to a certain strength to increase its own stability and meet the excavation conditions. Workers will drill many holes in the soil, then put in freezing pipes, use refrigerators to provide refrigeration liquid, and remove the freezing pipes after freezing, so that the soil will not melt for a long time.
However, although the freezing pipe was removed, the temperature was still below zero, and the workers seemed to be standing in front of the open refrigerator and wearing coats for construction. However, this big refrigerator has a bad temper and needs careful temperature control.
As long as the immersed tube method meets the mooring requirements of the ship, it is about1.5m.
Extended data:
Tunnel waterproofing
The main part of the underwater tunnel is in the rock and soil layer under the river and seabed. Being below the groundwater level all the year round, it bears all the head pressure from the water surface to the depth of the tunnel. Therefore, there are waterproof problems in underwater tunnels from construction to operation. The main waterproof measures are:
1, using waterproof concrete.
The production of waterproof concrete mainly depends on adjusting gradation, increasing cement content and sand ratio, so as to form a coating with a certain thickness around coarse aggregate and cut off the passage of capillary seepage along the surface of coarse aggregate to achieve waterproof and water-resistant effects.
2. Backfilling behind the wall
Backfilling behind the wall is to fill and grout the gap between the tunnel and the surrounding rock, so that the lining and the surrounding rock can be closely combined, the deformation of the surrounding rock can be reduced, the lining can be uniformly compressed, and the waterproof ability of the lining can be improved.
3, surrounding rock grouting
In order to improve the bearing capacity of surrounding rock of underwater tunnel and reduce water permeability, pre-grouting can be carried out in surrounding rock. Especially in the tunnel with drilling and blasting operation, the block stones around the tunnel can be reinforced by grouting to form a certain thickness of water stop and fill the cracks and fissures in the block stones, thus eliminating and reducing the effect of water pressure on the lining.
4. Double lining
Using double-layer lining for underwater tunnel can achieve two purposes. One is the need for protection. Under the action of explosion load, the surrounding rock may crack and destroy. As long as the lining waterproof layer is intact, there will be no large amount of water rushing into the tunnel, which will affect the traffic. The second is to prevent excessive water pressure. Sometimes, although waterproof concrete is used for backfill grouting, water seepage of lining is still inevitable under high water pressure.
In this case, the double lining can be used as a waterproof measure for underwater tunnels crossing the river.
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