Work finished on cross-bay tunnel-islands structures

Construction was completed on the 6.7-km dual six-lane subsea tunnel linking two 10-hectare engineered islands of the Hong Kong-Zhuhai-Macao Bridge (HZMB) on Oct 8.

The Islands-Tunnel Section spanning the Lingding Sea is the dominant engineering feature of the sea-crossing infrastructure connecting Hong Kong with Macao and Zhuhai.

For the first large immersed tunnel in open water in China's history, the world's most difficult comprehensive procedures were applied to ensure stable construction in depths up to 48 m below sea level.

After seven years, the final steps came with the dismantling of the island measuring platforms and steel-pipe piles of the temporary wharf. The work was done by a joint venture led by China Communications Construction Co Ltd (CCCC).

Ultra-large steel cylinder to be immersed in the sea

The completion came from having made the impossible into the possible from the beginning, said a project head.

Offshore construction commenced in January 2011 with geological surveys and piling works at the western man-made island's measuring platform.

Initial success was achieved on May 15 that year when the first ultra-large steel cylinder, installed with eight linked vibratory hammers, was immersed as a base for the Western Artificial Island. On Dec 7, 2011, the final steel cylinder for the Eastern Artificial Island, the 120th of the total, was sunk into the sea -- a remarkable engineering feat as the islands took shape the same year their construction began.

Sand compaction pile work spanned from Aug 14, 2011 to Aug 4, 2013, and was spread over 1.4 million cubic meters including island wall structures and transition sections of the immersed tunnel. It was the first time the technology had been utilized for so many applications in China.

Floating transport and installation of E30 immersed tube 

It took another four years, from May 2, 2013 to May 2, 2017, to complete 33 prefabricated immersed tubes -- each with a displacement of 80,000 tons -- and 12-m final joint weighing 6,500 tons. The grand project worked another wonder, achieving nearly 100 percent precision in butt joint installation -- meaning that the immersed tunnel in open waters has no leakage of any kind or degree.

Construction is now focused on paving the road surface, which began on Sept 11, 2017 and, according to an engineer, is due for completion before the end of November.

Hoisting construction on final joint closure [Photos by Chen Litong]