Chinese contractors five months ahead of schedule on 13.3km Nepal tunnel

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The TBM ahead of its launch last year. Image: Xinhua News

Chinese contractors China Railway No.2 Group and China Overseas Engineering Group are five months ahead of schedule on the construction of a complex 13.3km tunnel in Nepal.

So far, the contractors have completed 50% of the tunnelling mileage on the Nepal Sunkoshi Marin Diversion tunnel.

The project involves a tunnel boring machine (TBM) passing through the ‘Kathmandu spiral’ geological structure for the first time.

The tunnel will connect to a new 28.6 MW surface powerhouse on the Marin River to alleviate a power supply shortage in the area. It will also help to irrigate farmland in several surrounding districts by diverting water from the Sunkoshi River to the Marin River.

China Railway Group said that the tunnel passes through “unfavourable” geological areas with high water inflow zones, fault zones and squeezing ground.

All of this involved “great difficulty” and “increased construction risk”, it said.

To mitigate some of those risks, geological engineers have been surveying and reviewing the geology along the tunnel, carrying out deep drilling and supplementary surveys in the fault zone area to understand the site’s geological conditions.

The project started on 14 October 2022, when the contractors launched a 6.4m diameter Robbins double shield TBM. It has clocked up an average of 833.3m of drilling per month, and a maximum monthly distance of 1136m.

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