A Robbins Double Shield tunnel boring machine (TBM) has broken through about one year ahead of the overall project schedule, and seven months ahead of the TBM tunnelling schedule, at the Bheri Babai Diversion Multipurpose Project (BBDMP) in Nepal.
In a statement, Robbins said the breakthrough was achieved in April 2019., with the machine completing the 12.2km (7.5 mi) tunnel for the Government of Nepal’s Department of Irrigation (DOI) and contractor China Overseas Engineering Group Co. Ltd. Nepal Branch (COVEC Nepal).
Nepal’s first tunnel boring machine, at 5.06m (16.6 ft) diameter, achieved over 1000m (3300ft) monthly advance on two separate occasions and averaged over 700m (2300 t) per month over the course of tunnelling.
The machine’s completion of the tunnel in just 17 months came nearly a year ahead of the DOI’s deadline for completing the tunnel of March 28, 2020, with the contractor’s schedule being more aggressive.
The tunnel is located in the Siwalik Range, part of the Southern Himalayan Mountains, where geology consists of mainly sandstone, mudstone, and conglomerate.
“Using the TBM method instead of the conventional drill and blast method was the key factor for the success of this project,” said Mr. Hu Tianran, Project Manager for COVEC. “It has set a good example for the implementation of a large number of similar tunnels in Nepal’s water/energy/transportation projects in the future. There are promising prospects in the application of TBM technology in Nepal in my point of view.”
Once the BBDMP is operational, it will irrigate 51,000 hectares of land in the southern region of Nepal, and provide 48MW annual generating capacity. It will divert 42m3 (1,500 cubic feet) of water per second from Bheri River to Babai River under a head of 150m (490ft) using a 15m (49ft) tall dam, providing year-round irrigation in the surrounding Banke and Bardia districts. The estimated annual benefit in Nepalese Rupees is $2.9 billion for irrigation, and $4.3 billion for hydropower, making a total of NPR $7.2 billion (approx. US $64 million) in benefits once the project becomes active.