Design decisions

A bold design was required to provide room for major shipping lanes, and a traditional cable-stayed bridge was ruled out because the towers would be so high they would disrupt the approach of planes to the nearby Hong Kong International Airport.

Complex geological conditions underwater also had to be taken into account because the bed of the delta consists of unstable ooze rather than solid rock, meaning some traditional engineering options had to be abandoned.

Thus an offshore immersed tunnel was the only solution, and the design incorporated two artificial islands to connect the bridge with the tunnel.

Before the tunnel was completed at the end of last year, only a few offshore immersed tunnels longer than 3 km had ever been built - the Oresund Link between Denmark and Sweden, the Busan-Geoje Fixed Link in South Korea, the Chesapeake Bay Bridge-Tunnel and the San Francisco Yerba Buena Island Tunnel in the US.

Moreover, only a few countries had mastered key technologies for immersed tunnels. "We were eager to cooperate with foreign experts," Lin said.

However, as expensive consultation fees would put the project over budget, innovation became the only way forward, but it brought unforeseen pressures. "Can you imagine working on a project when you have no previous experience to rely on?" Lin said.

In addition, Chinese engineering's reputation rested on the team's success, so the work became more than just a job - it became a duty.

During the process, Lin's team mastered key technologies for immersed tunnel construction. It also made significant improvements and devised several innovations, which contributed to faster construction times, lower costs and most important, reduced safety risks.

To build the tunnel weighing millions of metric tons about 50 meters below the surface of the water, the team collaborated with other Chinese companies to employ gigantic tailor-made equipment.

None of the new technologies came easily, Lin said: "We faced tremendous pressures and risks every day. On this project, 3,000 people walked a tightrope, and meeting the challenge was a test of our power and ability to innovate."