Why is China building a bridge under the sea?

Added: 2026-05-24

[00:00:00]Imagine driving beneath the ocean floor, millions of tons of cedar pressing above you, while beneath your car lies a seamless fusion of concrete and steel assembled with near microscopic precision. It sounds like a scene from a science fiction movie, yet [music] it's a real triumph of modern engineering, the underwater tunnel. But how did humans manage to construct such colossal structures amid crushing water pressure, unstable sediments, and an environment completely isolated from the surface? In this documentary, Mandarin Tech takes you beneath the waves to uncover how humanity has turned the impossible into reality, creating breathtaking marvels hidden deep beneath the sea. Music in today's world, underwater tunnels play a crucial role in expanding human connectivity and reshaping global infrastructure. These monumental structures unite lands once divided by vast oceans, mighty rivers, or deep bays, sparking a revolution in transportation and logistics. Imagine traveling from one island to another or crossing a wide bay in just minutes without ferries or towering bridges, all made possible by underwater tunnels.

[00:01:11]Beyond saving time, they sustain the global flow of goods and people, ensuring trade moves swiftly, safely, and efficiently. For many nations, underwater tunnels have become vital arteries of economic and industrial growth, especially for port cities, while unlocking new opportunities for global commerce and regional development. Building an underwater tunnel demands exhaustive preparation and near-perfect design precision with every step calculated in detail to guarantee both feasibility and safety for the entire project. The first phase begins with comprehensive seabed surveys. Engineers study subsea topography, collect soil samples, and analyze rock strata to determine the geological structure, the bearing stability of the seabed, and any latent hazards that could affect construction.

[00:02:02]Alongside the technical work, environmental considerations are prioritized throughout planning and design.

[00:02:09]The project team must assess the tunnel's potential impacts on marine ecosystems, ensuring species are protected, and natural habitats are disturbed as little as possible. To achieve this, they implement noise mitigation measures during construction and may even install artificial reef structures to create new habitats for marine life. After the survey is completed, the construction step begins.

[00:02:36]The immersed tube method is one of the most widely used >> [music] >> techniques for constructing underwater tunnels. The process begins with the prefabrication of massive reinforced concrete segments on land.

[00:02:51]Each standard element measures approximately 217 m in length and weighs over 73,000 tons. Segments are manufactured with extreme precision to ensure perfect alignment and watertight sealing once submerged. Inside each segment, several compartments are designed for specific functions. Two main chambers for highway lanes, one for a railway line, and another service corridor dedicated to future maintenance and inspection. Once the sections are complete, they are transported to sea and carefully lowered into pre-dredged positions on the seabed using floating pontoons and specialized cranes. Each segment is then joined sequentially to form a continuous tunnel of the required length. The most critical phase of this method lies in the joint connections. If the seals are not handled with precision, seawater infiltration could pose serious risks.

[00:03:47]To prevent this, rubber gaskets are inserted between segments to ensure watertightness. While layers of sand and gravel are placed above and around the tunnel to prevent buoyancy caused by water pressure. Only after the connections are securely locked and stabilized are the temporary end bulkheads removed, transforming the individual tubes into a seamless, watertight tunnel.

[00:04:14]However, this technique is only suitable for areas with a stable seabed and gentle water currents. In environments with strong turbulence or complex underwater terrain, the immersed tube method becomes impractical due to difficulties in anchoring and maintaining waterproof integrity.

[00:04:35]Besides using the underground pipe lowering method, they also use the shield digging method to dig tunnels.

[00:04:41]The shield tunneling method, also known as tunnel boring machine, represents the most advanced technology in modern tunnel construction. A TBM operates as a colossal self-contained system capable of excavating soil, collecting debris, and installing reinforced concrete tunnel lining simultaneously in a continuous closed-loop process.

[00:05:03]This technique enables uninterrupted excavation beneath the ground or riverbeds while maintaining precision, safety, and minimal environmental disturbance.

[00:05:15]At the front of the TBM, lies a massive cutter head nearly 12 m in diameter and weighing over 200 tons.

[00:05:24]It is equipped with 140 high-strength steel cutting discs and blades rotating at approximately 2.7 revolutions per minute. As it spins, the cutter head exerts pressure up to 400 bar, enough to crush compact rock and soil. The excavated material is immediately drawn into the chamber behind the cutter head where foam and water are injected to maintain earth pressure balance, an essential factor preventing collapse in soft or water saturated ground. The slurry mixture is carried away on a continuous conveyor belt to the surface, where it passes through a discharge tower, mixed with lime to reduce moisture, and loaded onto trucks for disposal. Meanwhile, as excavation progresses, the TBM's rear section automatically installs precast concrete.