16,000 m continuous TBM drive sets new overseas tunnelling record in Sri Lanka

On 25 December 2025, a double-shield tunnel boring machine developed by China Railway Construction Heavy Industry Corporation achieved a continuous excavation exceeding 16,000 m at the Upper Elahera–Hela Canal Water Transfer Tunnel Project. The drive was completed without any intermediate inspection shaft, surpassing the 10,000-ring milestone and establishing a new overseas record for the longest single-heading excavation using a double-shield TBM. The machine, with an excavation diameter of 7.6 m, reached a peak monthly advance of 808 m and sustained an average of approximately 500 m per month, while maintaining availability above 95 percent.

The achievement is attributed to several design and operational innovations tailored to challenging geological conditions. A high-strength, high-wear-resistance rock-breaking system and long-life main drive enabled uninterrupted excavation throughout the full drive length. A key advancement was the integrated dual-support approach combining segmental lining with rock bolting and shotcreting. This configuration allowed rapid switching between support modes within one to two days, improving adaptability, safety, and construction efficiency.

The TBM was also equipped with an integrated probe and support system that consolidated probe drilling, core drilling, and rock-bolting functions. Advance boreholes up to 45 m deep were completed in under four hours, supporting effective real-time geological assessment ahead of the face.

Upon completion, the tunnel will form a critical component of Sri Lanka’s South-to-North Water Diversion initiative, addressing regional water scarcity and enhancing resilience against drought and flooding. Beyond its operational value, the project demonstrates how advanced TBM design and adaptive ground support strategies can deliver long, uninterrupted drives under complex ground conditions.