On June 20, Guangdong Transportation Group announced that the Shenzhen-Zhongshan Link, a mega project in the Guangdong-Hong Kong-Macao Greater Bay Area, has achieved another milestone. After about 24.5 hours of continuous operation, the first sloped tube segment of the immersed tube tunnel—segment No. 10 (E10)—was successfully joined underwater at a depth of 37 meters, bringing the completed length of the project's immersed tube tunnel to 1,608.5 meters.

The Shenzhen-Zhongshan Link is a mega cross-sea cluster project integrating bridges, islands, tunnels and an underwater interchange. Its subsea tunnel is about 6.8 kilometers long, including an immersed tube section of about 5 kilometers. Adopting a steel-shell concrete composite structure used for the first time in China and for the first time on a large scale internationally, it consists of 32 tube segments and one final joint and is currently the world's widest subsea immersed tube tunnel.

The E10 segment immersed this time is a standard segment, 165 meters long, 46 meters wide and 10.6 meters high, weighing about 80,000 tonnes. It is the first sloped segment and, together with the E9 segment, is located at the lowest point of the entire tunnel, equivalent to the tunnel's "silt trap." The tunnel site intersects the former Fanshi navigation channel, creating a "basin-bottom effect" that makes the siltation intensity markedly stronger than that of previously immersed segments. Meanwhile, as construction advances, immersed tube installation has moved from the deep-water area of the eastern trough of the "three shoals and two troughs" into the eastern shallow-shoal area, where terrain varies greatly and siltation in the shallow shoals and deep troughs is complex. Under the combined influence of recent repeated severe convective weather, large runoff during the flood season and dredging disturbance from nearby construction, abnormal siltation occurred for the first time since construction began.

"Under the changing and complex construction environment, the seawater density near the installed E9 segment varies greatly, posing a major safety risk of flotation. On the other hand, the deep water and deep trough also increase the sway amplitude of the E10 segment, making it more difficult to control the segment's posture and不利于 stable joining," said Ning Jinjin, deputy chief engineer of the Shenzhen-Zhongshan Link project department of CCCC First Harbor Engineering Co., Ltd.

At 2:20 p.m. on June 18, accompanied by a deep horn blast, the world's first immersed tube transport and installation vessel, berthed at the dock entrance of Guishan Island in Zhuhai, slowly set sail carrying the E10 segment. At 3:15 a.m. on June 19, escorted by Guangdong maritime authorities, the E10 segment arrived at the immersion site after a 50-kilometer long-distance floating transport. During immersion and joining, which coincided with an active ionosphere period and a high risk of signal loss, the Shenzhen-Zhongshan Link used the BeiDou satellite positioning system to dynamically monitor the entire installation process.

At 2:40 p.m. on June 19, after mooring, immersion, pulling and joining procedures, the E10 segment was successfully joined with the E9 segment. Breakthrough measurements showed that the joining accuracy of the E10 segment met the acceptance control standards.

Once completed, the Shenzhen-Zhongshan Link will effectively relieve pressure on the existing road network and is of great significance for improving the national expressway network and the comprehensive transportation system of the Pearl River Delta region, promoting industrial connectivity and efficient allocation of various factors in the Guangdong-Hong Kong-Macao Greater Bay Area, and accelerating the integrated development of the bay area's city cluster.