Nepal Sunkoshi Marin Diversion Tunnel Project is making substantial strides, with over 50% of the tunnelling work completed, outpacing the original schedule by a five-month margin, Tunnels and Tunnelling has reported.

China Railway No. 2 Group Co Ltd and China Overseas Engineering Group Co Ltd have successfully excavated more than 6.666km of the tunnel, with the project being the first TBM tunnel to traverse the Kathmandu spiral geological structure. The project’s Tunnel Boring Machine (TBM) is also the only high-buried, large-diameter single-head TBM tunnel currently under construction within Nepal.

Spanning 13.3km, the tunnel's path cuts through challenging geological terrain, including high water inflow areas, rock extrusions, geothermal obstacles, rock bursts, and a fault zone.

Since its launch in October the Robbins TBM, boasting a 6.4m diameter, has averaged a monthly progress of 833.3m, with a maximum of 1136m achieved In May.

To overcome the geological challenges, the TBM team implemented measures such as cutter adjustments, integration of over-excavation cutters, heightened grouting efforts, streamlined organizational processes, equipment upkeep, and efficient material and equipment supply management. The TBM's tapered design further reduces the risk of becoming trapped in challenging ground conditions.

The project's tunnel will be connected to a 28.6MW surface powerhouse along the Marin River, developed to bolster the region's electricity supply. It will also increase farmland irrigation in Dhanusha, Mahottari, Sarlahi, Rauthat, and Bara districts within the Terai Plain.

by waterpowermagazine