In Nepal’s Sindhuli District, a tunnel boring machine (TBM) broke through 11 months ahead of schedule on May 8, marking a significant milestone for the Sunkoshi Marin Diversion Multipurpose Project (SMDMP). The 6.4m diameter Robbins Double Shield machine successfully navigated challenging geology to complete the 13.3km tunnel, making it one of the longest TBM-driven tunnels in the Himalayan region and the second such tunnel completed in Nepal.

“The overall design of the Robbins TBM is proven, and the equipment’s performance and integrity are excellent. Additionally, its adaptability to the Himalayan geological conditions is very impressive,” said Mr. Liu Fengfan, SMDMP Project Manager for contractor B-2/COVEC.

The TBM faced challenging geology, including two major fault zones with varying rock types like mudstone, sandstone, conglomerate, quartzite, and granite. The Sunkoshi Marin tunnel, mostly bored through igneous rock, had a maximum overburden of 1,320m.

The machine and crew overcame multiple instances where the shield became trapped, requiring bypass tunnels to free it. One significant incident, 4km into the tunnelling, took 27 days to resolve. Despite these challenges, the team achieved swift advance rates, including a project record of 1,503.3m in one month and 72.6m in one day in March 2024.

The TBM’s success is attributed to its proven design. Originally used at a smaller diameter on Nepal’s first TBM-driven tunnel, the Bheri Babai Diversion Multipurpose Project (BBDMP), the machine was refurbished and upgraded to 6.4 meters in diameter with new front shield components assembled onsite. “One of the highlights is that this machine integrates the overall structure of the 5.06m diameter TBM from the Bheri Babai project. After upgrading to 6.4 m diameter, all new front shield components were not assembled in the factory. Instead, we adopted Onsite First Time Assembly (OFTA). This was very effective, and I find it particularly noteworthy,” said Mr. Jin Haikuan, Deputy Project Manager & TBM Production Manager for B-2/COVEC.

With the tunnelling complete, the project will now focus on providing power and water. The tunnel connects to a new 28.6MW powerhouse on the Marin River, which will help alleviate power shortages in the area. It will also facilitate farmland irrigation in the Terai Plain districts of Dhanusha, Mahottari, Sarlahi, Rauthat, and Bara by diverting water from the Sunkoshi River to the Marin River. The Department of Water Resources and Irrigation under Nepal’s Ministry of Energy, Water Resources & Irrigation oversees the project.

“B-2/COVEC and Robbins have successfully introduced and spread TBM technology in Nepal and shown the advantages of it. This country needs more tunnels,” said Robbins President Lok Home at the breakthrough ceremony. “To have these good performances on these first two projects is really a good thing for the country and our industry.”

Sunkoshi Marin
The Robbins TBM and its crew overcame challenging geology to achieve swift advance rates including an impressive 1,503.3m in one month.