On December 29, Guangdong Provincial Transportation Group announced another milestone: the E28 tube section of the Shenzhen-Zhongshan Link immersed tunnel has been successfully immersed and installed. To date, 20 tube sections of the Shenzhen-Zhongshan Link have been joined, with an installed length of 3,052.8 meters, accounting for approximately 61% of the total immersed tube section length.

The Shenzhen-Zhongshan Link is a cross-sea cluster project integrating bridges, islands, tunnels and underwater interchanges. Its subsea tunnel is 6,845 meters long, including a 5,035-meter immersed tube section composed of 32 tube sections and one final joint. It is the world's first two-way eight-lane steel-shell concrete immersed tunnel.

The E28 tube section installed this time is a non-standard section that is ultra-wide and variable-width. It was constructed by the S08 contract section of the Shenzhen-Zhongshan Link project under the consortium of Poly Changda and Guangzhou Salvage Bureau.

In the early hours of December 28, the E28 tube section departed from the Nansha Longxue basin in Guangzhou for the tunnel site, towed by a tugboat fleet with a total horsepower exceeding 44,000. Due to the combined effects of the recent Typhoon Rai and strong cold air, wind, waves and temperatures in the construction sea area changed sharply, bringing many adverse factors to the floating transport and installation of the immersed tube. To address this, the construction team carefully planned and integrated resources. After completing the removal of outfitting components for the E29 tube section, they promptly carried out secondary outfitting of the E28 tube section and foundation construction in the tunnel site area, seizing the construction window. They used a gravel leveling vessel to carry out gravel foundation laying around the clock, achieving a leveling accuracy with an error of no more than 2.5 centimeters, overcoming the technical challenge of laying extremely fine-leveled gravel foundations in a nearshore environment with strong back-silting, and laying a solid foundation for the successful joining of the E28 tube section.

In addition, the construction team adopted a self-developed visual immersed tube joining system, which dynamically captures subtle measurement errors caused by deformation of the tube section under water pressure. Using anchor block tension sensors and the system's autonomous analysis and correction functions, the absolute accuracy of the measurement system was further improved, keeping the installation accuracy of the tube section at the millimeter level.

"The E28 tube section is the fifth tube section joined on the east side of the project's immersed tunnel. With millimeter-level joining accuracy, we have exceeded the annual construction target. The immersed tube floating transport and installation technology of the Guangzhou Salvage Bureau construction team also provides a solution for the refined control of towing curved, irregular tube sections by multi-tugboat fleets over long-distance complex routes in open sea," said Li Wanghui, chief engineer of the Guangzhou Salvage Bureau's Shenzhen-Zhongshan Link project.

At 14:00 on December 29, after nearly 7.5 hours of fine adjustment, immersion, pulling and joining, and hydraulic connection procedures, the E28 tube section completed joining and installation at a depth of about 25 meters underwater. At 17:30, a tripartite joint breakthrough measurement confirmed that both the absolute and relative installation deviations met the requirements of the design and acceptance standards.

To address technical challenges such as ultra-width, deep burial, variable width and large back-silting in the Shenzhen-Zhongshan Link immersed tunnel, the construction team applied a new steel-shell concrete immersed tunnel structure in China for the first time. "To overcome the challenge of filling closed compartments with vibration-free concrete to full density, we developed high-fluidity self-compacting concrete, independently developed intelligent casting equipment and systems, and summarized and refined a three-dimensional numerical simulation technology for the forces acting on tube sections during casting. Through intelligent casting, we achieved 100% concrete filling density," said Su Zongxian, chief engineer of the Poly Changda Shenzhen-Zhongshan Link project.

At present, construction of the Shenzhen-Zhongshan Link is progressing steadily. This year, 14 tube sections of the immersed tunnel have been immersed and joined, bringing the cumulative total to 20 of the 32 tube sections across the entire line. Construction of the east and west artificial islands is proceeding in an orderly manner. The main towers and anchor blocks of the Lingdingyang Bridge have been completed, and the main cable saddles have been hoisted. Box girder erection is underway on the Zhongshan Bridge.