The Tung Chung Line Extension project uses the tunnel boring machine (TBM), “XIHE”, to construct a tunnel section of about 1.3 km from Tung Chung Station to the future Tung Chung West Station. “XIHE” recently completed the up-track tunnel breakthrough to Tung Chung West Station and the U-turn operation and has just embarked on the down-track tunneling journey towards Tung Chung Station, marking a new milestone for the project.

Starting from earlier this year, “XIHE” has simultaneously carried out tunneling and tunnel lining installation, passing through the mountain and beneath the sea. After about nine months, it completed its first underground journey to the future Tung Chung West Station in mid-October.

This journey was challenging, but “XIHE” overcame it with three key advantages:

1) The Variable Density TBM can flexibly handle different slurry and soil densities.
2) Experienced operators adjust tunneling pressure meticulously based on geological characteristics identified in pre-construction surveys.
3) Professional maintenance, including regular replacement of worn cutter discs, ensures optimal TBM performance.

With these advantages, “XIHE” successfully overcame challenges, ranging from hard rock and mixed soil layers to underground water pressure, to complete its mission.

Traditional methods require disassembling the TBM and transporting it to another launching shaft for reassembly. But in this case, the project team employed the push-pull method and a Self-Propelled Modular Transporter after precise calculations and planning to turn around and reassemble the 100-metre-long, 1,000-tonne TBM inside the shaft in stages after completion of the up-track tunnel to Tung Chung West Station’s shaft, to prepare for the down-track tunnelling. This is the first time a TBM U-turn operation has been conducted in an MTR new railway project.

Though the innovative U-turn operation is more demanding in terms of operation and space, it brings several benefits:

1) Reduces large-scale lifting operations
2) Minimizes ground transportation
3) Reduces noise
4) Saves about half the construction time
5) Reduces space requirements, eliminating the need for long shafts and a large noise enclosure

In short, the U-turn operation not only speeds up and improves tunnel construction efficiency but also enhances safety and reduces community impact.

After the U-turn operation, “XIHE” underwent thorough inspection and maintenance and has successfully started the down-track tunnelling mission towards Tung Chung Station.

The project team will continue to rigorously advance the remaining tunnelling works, aiming to complete the second tunnel by 2026.