At the bottom of Shantou Bay, a landmark tunnel, the Shantou Bay Undersea Tunnel, has recently been successfully completed. This tunnel is not only the world's first single-hole double-track high-speed railway tunnel with a speed of 350 kilometers per hour, but also marks the significant progress made in the transportation artery connecting Shantou and Shanwei, and also writes a number of new records in the history of undersea tunnel construction at home and abroad.

The Shantou high-speed railway, a project contracted by China Railway Design Group Co., Ltd., is an important passage connecting Shantou and Shanwei in Guangdong Province, and is also a key part of the coastal corridor of the national "eight vertical and eight horizontal" high-speed railway network. The 9,781-meter-long Shantou Bay Undersea Tunnel is not only a control project for this high-speed rail line, but also the biggest challenge faced by the engineering team.

In a seismic zone of 8 degrees, the tunnel needs to cross 17 fault fracture zones, including 8 active faults. The ultra-high water pressure of nearly 1Mpa and the strong corrosive seawater on the seabed also put forward strict requirements for the construction of the tunnel. In the face of these complex geological and marine environments, the project team has demonstrated outstanding innovation and technical prowess.

In order to cope with the huge pressure of seawater, the project team mastered the pressure state of seawater at the time of the earthquake for the first time, and implemented high-precision ultra-high pressure 100-meter-level sea surface grouting construction in the main channel of the bay, which effectively reduced the water seepage and pressure of the tunnel. This innovative measure not only improves the stability of the tunnel, but also opens a new era of grouting construction for railway tunnels.

The project team has also achieved remarkable results in reducing the impact of earthquakes on high-speed rail operations. They have developed flexible and retractable shock-absorbing joints and flexible seismic isolation layers, which are innovative designs that can keep the tunnel stable in the event of an earthquake, achieving the effect of "overcoming rigidity with softness". This breakthrough not only improves the seismic performance of the tunnel, but also provides a strong guarantee for the safe operation of the high-speed railway.

Faced with the challenge of high corrosiveness of seawater, engineers proposed a combined waterproof and anti-corrosion defense system, including measures such as limited discharge and pressure reduction, comprehensive waterproofing and high-strength crack resistance. Through trial and error and adjusting the concrete mixture, they pioneered the ice-water low-temperature mixing process and developed a new type of anti-crack material. This innovative achievement successfully solves the problem of difficult maintenance and easy cracking of high-strength concrete tunnels.

The successful breakthrough of the Shantou Bay Undersea Tunnel has not only created a number of records for the construction of deep-sea tunnels, but also injected new impetus into the development of China's high-speed rail industry. This tunnel is not only the world's first single-hole double-track high-speed railway undersea tunnel with a speed of 350 kilometers per hour, but also the world's largest excavated railway undersea tunnel. It is also the railway undersea tunnel with the most active faults in China and the undersea tunnel with the largest water pressure in China.

With the completion and opening of the Shanshan high-speed railway, this high-speed railway line will be connected to the Zhangshan high-speed railway under construction, forming a new north-south high-capacity passenger transport channel. The construction of this corridor will provide more convenient and efficient transportation links for cities in the Pearl River Delta, Haixi and Yangtze River Delta, and further promote the economic development and regional integration of cities along the route.(This article is from the official website of Seetao www.seetao.com. Reprinting without permission is strictly prohibited. Please indicate Seetao.com + original link when reprinting) Seetao.com Strategy Column Editor/Sun Fengjuan