One thing is clear. The past decade or so has seen a drastic change in the machinery used for tunnelling construction in India. “Whereas conventional blasting methods used to prevail, which made for very slow progress, now the most prevalent method in the Himalayan region is the New Austrian Tunnelling Method (NATM),which helps adjust to site conditions and has significantly sped up the implementation of projects,” observes Ranvir Singh, Manager (Projects)and Contracts Management Expert (Tunnelling), PEMS Engineering Consultants. “Cost comparisons of the two prominent tunnel construction methods nowadays and geological conditions, particularly in the Himalayan region, favour the NATM overtunnel boring machines (TBMs).”

“TBMs in general haven’tbeen successful in Himalayan geology owing to heterogeneous rock strata,” agrees Col Deepak Patil, General Manager (Project), Silkyara Tunnel, National Highways & Infrastructure Development Corporation. “For tunnelling in the Himalayan region, India mostly uses machinesthat can perform activities associated with the NATM, such asboomers/jumbos, shotcreting, various kinds of grouting, strengtheningthe ground, rather than TBMs.”

In cities where metro projects are being implemented, TBMs are being extensively used. Going forward, to take tunnelling to the next level, we must think of tunnelling methods beyond TBMs, NATM and conventional methods, based on rock mechanics and properties, advises Dr B C Mandal, Executive Director (Technical), BPC Consultant India.

Improving techniques

To ensure that proper methods and machinery are engaged, we need geological engineers to lead tunnelling projects instead of the civil engineers who are currently at the forefront of tunnelling projects, says Dr Mandal.

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