The excavation will form one of two identical tubes, beneath Su'ai Bay, each 3.05km-long with a 14.5m external diameter.

The two three-lane road tunnels aim to improve links between both sides of the city of Shantou, located around 300km east-north-east of Hong Kong.

In terms of construction, the project is regarded as the most challenging project of its kind in China. Geology along the tunnel alignment comprised mainly medium-coarse sand, muddy soil, mud, muddy sand and granite. As a result, the TBM overcame numerous difficulties and challenges, including boring in a high-intensity earthquake zone, with shallow overburden, hard rock and other complex mixed-ground conditions.

Accordingly, CREG customised the TBM to feature an integrated ultra-high-pressure sustaining system, accessible cutterhead, spherical main drive and twin-circuit air pressure control.

Thanks to various simulations, targeted devices, information management and optimised cutters, the drive was accurately controlled throughout.

The TBM’s best performance turned out to be 25m in one day, 150m in a week and 460m in one month.