Recently, the Shantou Bay undersea tunnel under the Shantou Shanwei Railway received the "first gun", the world first designed high-speed tunnel at speed of 350 km/h, with a single hole and two lines, has officially entered the substantive construction stage.
picture //Shanshan Rail Line
Shantou - Shanwei Rail Line is to be connected to the Rail Line of Guangzhou - Shantou, which will be further put the cities of Guangzhou, Huizhou, Shanwei, Shantou city closely tied together. Meanwhile, these rail lines will connect the railways of Xiashen, Ganshen and Guangshen lines, which will speed up the urbanization of the areas along these rail lines and will form a new high-speed railway economic belt, boosting the revitalization of the region of east Guangdong, shortening the gap between the development of this region and other regions of the Pearl River delta, which is set to promote the economy development in a balanced and coordinated manner.
According to the plan, Shantou Shanwei Railway to the east will also connect Shantou to Zhangzhou railway, and together with Hangzhou-Wenzhou railway, Hangzhou-Taizhou Railway, Wenzhou-Fuzhou Railway and Fuzhou-Xiamen Railway, jointly constitute a new high-speed railway with large capacity passenger channel along the southeast coast.
Shantou Bay Undersea Tunnel is located in Shantou City, Guangdong Province. It runs through Shantou Bay between Mayu Island and Dezhou Island in the lower reaches of Shantou Bay Bridge. The tunnel is 9781 meters in length and is a control project of the whole Shantou Railway.
Highly-intensive earthquake zone passes through a dense fault rupture zone
Shantou Bay undersea tunnel passes through 17 fault rupture zones in the 8-degree earthquake zone, among which 8 are active faults, which are the most underwater tunnels at home and abroad.
Schematic diagram of fault fracture zone distribution in Shantou Bay Submarine Tunnel
High water pressure in the sea
Most of the tunnels are located in the high-risk area of high water pressure, with the maximum water pressure up to 0.97 mpa. Under such strong pressure, water can form a column up to 97 meters high, making it the largest underwater tunnel in China.
According to such underwater environment, the construction personnel should adopt appropriate technical means to ensure the tunnel structure is safe, waterproof and reliable, and the operation cost is controllable.
High grade erosive environment in sea area
Due to the long-term existence of the Tunnel in high-pressure seawater environment, the tunnel structure of Shantou Bay needs to adapt to the strong erosion environment while bearing the high water pressure seepage action, and the combined action of the two results in the more severe environment of the tunnel.
Complexity of geological conditions
Taking shield section as an example, the excavation process of this section of tunnel is likened to "cutting tofu before grinding pig iron, sandwiched between soft and hard" by the construction personnel, when the extremely soft and hard strata are transferred from the extremely soft stratum of silt to the extremely hard stratum of weakly weathered granite.
Schematic diagram of engineering geology of Shantou Bay Undersea Tunnel
The sea area is full of difficulties, while the land area is not easy either. With an external diameter of 14.53 meters, the super-large diameter shield tunneling machine also faces severe challenges in the beachhead section of the north bank: continuous complex geological environment and strata, continuously running under or adjacent to the construction facilities along the Shenhai Expressway, Zhongtai overpass and high voltage tower.
Varieties of construction mode
Due to the strict construction environment, complex engineering geology and hydrogeology conditions, high construction risks, and time limit, the tunnel adopts a total of 6 construction methods in different sections, with complex and diverse construction methods and changeable process connections.
Schematic diagram of Construction method of Shantou Bay Undersea Tunnel
Shantou Bay undersea tunnel has made quite a few breakthroughs in the fields of underwater tunnels, railway tunnels and super-large diameter shield tunnels at home and abroad. It has brought challenges to the builders in geological structure complexity, seawater pressure class, design and construction difficulty, operation standard and risk control and other aspects.
source:China railway
