China is building a tunnel under the sea for its high speed. It has already reached a record depth

Under the seabed, dozens of meters deep, there is a work that is progressing with a minimal margin of error. It cannot be seen from the surface, but it is part of a railway infrastructure key in southern China. According to CGTN, the country has reached a new milestone in the construction of a high-speed underwater tunnel: the excavation has already reached 113 meters under the seabed. The figure is not minor, because it places the work at a point where the geological conditions and water pressure significantly increase the technical difficulty.

This advance is part of a much larger infrastructure that is taking shape in the south of the country. The 116-kilometer Shenzhen-Jiangmen high-speed line is designed to connect both cities in less than an hour, integrating into the rail corridor that runs along the Chinese coast. In this way, the project has entered a particularly demanding phase, in which the tunnel under the Pearl River estuary becomes one of the most technically complex points of the entire work.

A section under the sea that concentrates the greatest technical challenge

At the center of this phase of the project is the underwater infrastructure that requires refinement of each step. To execute it, the work relies on a large diameter tunnel boring machine developed in China. The machine, known as “Shenjiang-1”, has kept the excavation going continuously, even during festive periods such as Qingming. It not only drills the ground, it also allows progress while the interior lining of the tunnel is being built, a system that seeks to gain efficiency in one of the most delicate points of the route.

From there, the challenge stops being just mechanical and becomes conditioned by the terrain. The TBM must traverse 13 different strata, with five types of composite geology and six fault zones along the route. These types of conditions force the operation to be constantly adjusted, because each layer can respond differently to the excavation. In this context, moving forward does not depend solely on the power of the machinery, but also on maintaining control in a challenging environment.

Added to this complexity of the terrain is a less visible, but equally determining factor: the pressure of the water at those depths. The tunnel is planned to reach a maximum of 116 meters below the seabeda level at which hydraulic conditions become especially demanding for the machinery and the structure itself. To operate in this environment, the system uses a sludge circuit that fulfills a double function: on the one hand, it reduces friction at the excavation face and, on the other, it transports the extracted material to the surface, where it is separated and reused in the process.

CCTV, China’s largest state television network, shows the progress of the excavation

While the machine advances, the tunnel is not far behind. Just behind the excavation face, the teams are assembling the prefabricated concrete segments that form the interior lining. Each one measures around two meters wide and nine are needed to complete a ring in a structure that exceeds 13 meters in diameter. This system allows excavation and construction to progress at the same time, reducing time and helping to maintain the pace of execution.

The magnitude of this work is better understood when put into perspective. Official information indicates that this section extends over 13.69 kilometers and crosses several waterways at the mouth of the river, located between Dongguan and Guangzhou. It is a key piece within a line designed to improve the connection in the Guangdong-Hong Kong-Macao Greater Bay Area. Beyond the depth already achieved, the project seeks to strengthen regional connectivity and support economic integration in one of the most active areas of the country.

Images | CGTN

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