Installation of the 12th immersed tube of the Hong Kong-Zhuhai-Macao Bridge subsea tunnel completed

      Construction begins after 8 rounds of immersion operations
      At 19:00 on August 18, escorted by more than 10 vessels, the 12th immersed tube began to be warped out of the dock, and then a towing formation composed of 8 tugboats was assembled; the immersed tube floated on the sea surface and was towed to the installation area. After 5 hours of towing, the tube section arrived smoothly at the construction area at 4:30 on the 19th for mooring operations.
      At 13:30 on August 19, the tube section began to be filled with water and sunk. After 8 rounds of immersion operations, the bottom of the tube section reached a point 2 meters above the foundation bed. Operators adjusted the posture of the tube section, and after on-site verification by divers, the tube section was steadily seated on the bed, and the joining construction began. The hydraulic connection operation was successfully completed at 23:00.
      Terrain and currents increase construction risks
      A person in charge of the general manager's department of the CCCC Hong Kong-Zhuhai-Macao Bridge Island and Tunnel Project said that the immersed tube tunnel of the Hong Kong-Zhuhai-Macao Bridge consists of 33 tube sections, of which 19 are installed at a water depth of more than 40 meters. The overall alignment is W-shaped, making it the world's first deeply buried deep-water immersed tube tunnel. Tube section E12 weighs about 80,000 tons. Its installation area is located in the Lingding main navigation channel, with a foundation trench depth of about 30 meters. Its stern end is the deepest point of the tunnel (the first low point of the W shape), with an actual installation water depth of more than 45 meters. It is a typical tube section in a deep-water, deep-trench, and navigation channel area, and its installation is highly difficult.
      The person in charge explained that the foundation trench of the subsea tunnel and the Lingding navigation trench cross at nearly 90° in the E12 tube section area. The installation terrain is complex, and the currents in the trench are even more variable, making tube section control difficult and increasing the overall construction risk. The construction area is broad and long, about 480 meters from the Lingding temporary navigation channel currently in use. Affected by factors such as the closure of the Lingding navigation channel, the successive opening of the Lingding temporary navigation channel and the Longgu West navigation channel, and the just-ended fishing moratorium, the navigation rules for social vessels have been disrupted. In addition, formation assembly and towing are both carried out at night, creating high risks for navigation safety control. For the 180-meter-long tube section foundation bed, the height difference between bow and stern is only 0.5 meters, and the height difference between two adjacent gravel ridges is less than 1 millimeter. The foundation bed laying requires high precision. Under the influence of the complex environmental conditions of deep water, deep trenches, and the main navigation trench, longitudinal slope control for the tunnel is highly difficult.