The main construction methods used to build underwater tunnels are: open-cut embankment method, pneumatic caisson method, shield method and immersed tube method. The open excavation method for embankment is more economical and should generally be considered first when conditions permit. The pneumatic caisson method is only suitable for smaller rivers where there is not much shipping.
Since the shipping traffic in places where underwater tunnels need to be built is usually relatively frequent, the use of open excavation methods and pneumatic caisson methods will greatly interfere with water traffic. Therefore, shield tunneling has been mostly used in the construction of underwater tunnels for more than 150 years. method and immersed tube method.
After the 1950s, major technical key breakthroughs such as the underwater joints and foundation treatment of the immersed tube method were successively made, which greatly simplified the construction process and greatly improved the waterproofness of the tunnel, and it can be used Rectangular section to accommodate more than four lanes.
Under certain conditions, the immersed tube method tunnel has shallow soil cover, short lines, low lighting and ventilation costs, low engineering and operating costs, and good use effects. Therefore, since 1965, 20 tunnels have been built in various countries around the world. Most of the underwater road tunnels adopt the immersed tube method.
Open cut method: drainage, digging a deep pit, then construction, and finally filling. This method is the simplest, but the construction site is large and restricted by surrounding buildings. Suzhou Dushu Lake Tunnel and Wuhan East Lake Tunnel have adopted this approach.
Shield tunneling method: the most commonly used and advanced method in tunnel construction. It started in the UK and flourished in Japan with a history of more than 180 years. Its biggest advantage is that it is suitable for tunnel excavation in soft soil.
Freezing method: freeze the soil to reach a certain strength, increase its own stability, and meet the excavation conditions. Workers will drill many holes in the soil, then put freezing tubes in, use the freezer to provide refrigerant fluid, and remove the freezing tubes after freezing, so that the soil will not melt for a long time.
However, although the freezing pipe was removed, the temperature was still more than ten degrees below zero. The workers seemed to be standing in front of the refrigerator with the door open, and they had to wear coats for construction. However, this large refrigerator is not very good-tempered and requires careful temperature control.
For construction using the immersed tube method, as long as it meets the anchoring requirements of the ship, it is about 1.5m.
Extended information:
Tunnel waterproofing
The main part of the underwater tunnel is in the rock and soil layer under the river and seabed. It is below the groundwater level all year round and bears the full head pressure from the water surface to the depth of the tunnel. Therefore, underwater tunnels have a waterproofing problem from construction to operation. The main measures for waterproofing are:
1. Use waterproof concrete
The production of waterproof concrete mainly depends on adjusting the gradation, increasing the cement amount and increasing the sand rate so that it can be used around the coarse aggregate. It forms a wrapping layer of a certain thickness and cuts off the passage of capillary water along the surface of the coarse aggregate to achieve the effect of waterproofing and water resistance.
2. Backfilling behind the wall
Backfilling behind the wall is to fill and grout the gap between the tunnel and the surrounding rock, so as to tightly combine the lining with the surrounding rock and reduce the deformation of the surrounding rock. Make the lining evenly pressurized and improve the waterproofing ability of the lining.
3. Surrounding rock grouting
In order to increase the bearing capacity and reduce water permeability of the underwater tunnel surrounding rock, pre-grouting can be performed in the surrounding rock. Especially for tunnels that use drilling and blasting operations, grouting can consolidate the massive rocks around the tunnel to form a waterstop of a certain thickness, and fill the cracks and fissures in the massive rocks, thereby eliminating and reducing the impact of water pressure on the lining. role.
4. Double-layer lining
Using double-layer lining in underwater tunnels can achieve two purposes. The first is the need for protection. Under the action of explosive loads, the surrounding rock may crack and damage. As long as the lining waterproof layer is intact, there will be no large amount of water gushing in the tunnel and affecting traffic. The second is to prevent high water pressure. Sometimes, even if waterproof concrete backfill grouting is used, lining seepage will inevitably occur under high water pressure.
In this case, double-layer lining can be used as a waterproofing measure for the river-crossing section of the underwater tunnel.
Baidu Encyclopedia-Underwater Tunnel