Tunnel Boring Machine in Nepal
A tunnel is an underground passage that is mainly used for water conveyance and
transportation. Construction of a tunnel is a difficult and risky job to
perform and it requires highly skilled manpower and systematic construction practice. In
Nepal, mainly Drilling and Blasting Method (DBM) has been used in tunnel
construction practice but recently the successful use of Tunnel Boring Machine
(TBM) in the construction of 12.208 KM tunnel in Bheri Babai Diversion Multipurpose
Project (BBDMP) has brought a new dimension in tunnel construction practices in
Nepal.
In Tunnel Boring Machine (TBM), rotating cutter wheel excavates soil, mechanical discharging machine mucks the soil and the TBM itself places the primary ground support such as concrete segment, soil rock bolts, steel ribs, meshes, shotcrete, etc. resulting in the formation of the stable tunnel crosssection. This integrated system procedure in TBM has resulted in a significant enhancement in tunnel construction speed. The tendency of contractors to leave the site without completing the project will be eliminated with this technology as once the machine starts to excavate, the machine cannot be retracted unless and until it reaches the final point. This will lead to the completion of the project on time.
The quality control in Tunnel Boring Machine Method is much easier in comparison with the Drilling and Blasting Method. This results in a better quality of work and longer life of the tunnel. Not only quality but the speed of construction in the TBM method is about three times faster than the DBM method. Similarly, the Tunnel boring machine reduces disturbance in the excavation area, which makes it ideal for use in heavily urbanized areas. TBM also produces a smooth tunnel wall that reduces the cost of the final lining.
Tunnel Boring Machine being advanced and having integrated system has larger dimensions and is heavy which leads to a lot of trouble in transporting and setting it on site. In the case of the Bheri Babai Diversion Multipurpose Project (BBDMP), the entry portal site was made flat for about 130m and a further 180m tunnel was excavated using the Drilling and Blasting Method for the setting of TBM on-site. Similarly, in order to take its heavy component to the site, the transporting route was inspected and checked for safety. So this might lead to difficulty in transporting large parts of TBM in the remote terrain of Nepal.
In conclusion, considering the speed and quality of tunnel construction work, the future of Tunnel Boring Machine Method (TBM) in Nepal looks promising and the Government of Nepal shall make easy and motivating provisions for its implementation in the tunnel construction practice.
Special thanks to Er. Jagadiswar Man Shrestha Sir for providing information about Bheri Babai Diversion Multipurpose Project (BBDMP).
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