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, NATMs and conventional methods, based on rock mechanics and properties.
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 over tunnel boring machines (TBMs).” he adds.
“TBMs in general haven’t been 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 machines that can perform activities associated with the NATM, such as boomers/jumbos, shotcreting, various kinds of grouting, strengthening the ground, rather than TBMs.” he says
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.
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. “Then, wherever a modern equipment is available that is superior to conventional drilling and blasting, the engineer can specify its use in the contract, such as using a road header machine instead of drilling and blasting.”
Need To Fill Gaps In The Availability Of Technology.
To speed up the geological investigations that precede projects, we need mobile variants of bore machines or modern technology and models that offer more precise results faster, says Singh.
“Also, with a blast happening every six to eight hours, we need more mobile variants of shotcreting equipment to implement tunnel projects faster and meet tight project deadlines. Blasting is always controlled but, even so, some vibration still occurs that impacts the surrounding area. More environment-friendly blasting techniques are welcome.” he says.
A major concern about tunnelling machines in India is the high cost, an outcome of the machines being imported. “Consequently, the maintenance and support of these machines is very time-consuming because the parts come from overseas and are similarly expensive,” observes Patil.
“We’re using TBMs in the Himalaya geology to successfully bore through anything from hard rock to sand, but the fact that these machines are imported creates major operational challenges when something goes wrong,” points out Shubham Shrivastava, Tunnel Engineer, AECOM India.
There is a pressing need to indigenise tunnelling equipment as far as possible to increase the deployment of modern machinery,reduce the costs and cut short service timelines. Among the key equipment that should be made in India, Patil counts heavy-duty loaders, Liebherr excavators (for loose strata), telehandlers, grouting pumps, Schaeff loaders, drum cutters, hydraulic crawler drill machines, side-dumping loaders (such as the CAT 850 model), etc.
“We’re missing the indigenous production of semi and fully automatic drill jumbo machines, semi and fully automatic shotcrete machines for NATM tunnelling, advanced technology in TBMs manufactured for mining (such as advance probing and tunnel seismic prediction technology) and advanced equipment for cross-passage structure execution (to ease smooth construction in confined spaces),” says Ram Gopal Saini, Founder, Promoter and Director, Mega Metro Engineering.
“Slurry TBMs have a lot of potential in India in mixed geological strata but as all the TBMs in India are imported, a lot of the ancillary components could be indigenised.” he says.
How Would These Technologies Improve Tunnelling In India?
“Automated boomers can drill more accurately without any outbreak and matching the excavation line,” explains Saini. “With the use of manager measure while drilling (MWD) software, the drill and blast process can be optimised still further for underground works. Automated drilling increases productivity and safety while reducing the cost.”..
Further, probing the geology in advance and making good predictions using technology can help TBMs avoid getting stuck in mountainous terrain as well as in city underground metro projects, he continues.
Once a TBM is stuck, its retrieval by a new shaft or resolving a complex situation naturally delays the project execution. During the construction of the Golcha Shaft on the DMRC Phase 3 CC05 (heritage line), for the retrieval of a stuck TBM, many unchartered utilities of multiple disciplines—civil, electrical and telecom—were encountered, adding to which traffic management in a limited road space was a concern.”
Insufficient training is why many operators lack machinery knowledge and are unable to face the challenges that arise in tunnel constructions, opines Shrivastava. “Major equipment breakdowns are also attributed to insufficient training, which affects the progress of projects.”..
“Proper operator training would improve the efficiency at work as well as onsite safety,” continues Shrivastava. “As tunnel engineers, we know the consequences of each activity but workers are illiterate and need to be guided especially when approaching equipment. Worker safety is the biggest challenge in tunnelling. It helps to have very skilled machine operators.”..
Essentially, “we have too few operators trained in using tunnelling machines because we lack institutes imparting such training,” points out Patil. He proposes that the Government should offer training through ITI-styled schools and offer the trained manpower to the infra industry.
Exactly What Sort Of Training Is Needed?
Singh emphasises that “operators must be made more efficient and especially trained in using automated versions of machines like boomers to speed up drilling”.
“We need more operators trained in boomers, shotcrete machines, heavy-duty tippers, rock breakers,loaders and excavators,” adds Patil.
“For the best outcomes with TBMs, training the deployed workers in the electronic PLCs [program logic control] and hydraulic system is very essential,” says Saini. “After commissioning, the TBM manufacturer should post experts onsite until the machine has moved forward a minimum 100 m or so, to acclimatise the deployed team and help them to fully understand the TBM functions. Also, the TBM manufacturer should also support regular servicing in complex situations as well as the setting up of a cutter disc repair workshop for economical operations.”..
“The non-availability of NATM-qualified engineers as well as good geotechnical experts is also a concern,” adds Patil.
Is Anyone Listening?
All modern tunnelling technologies can be had in India for a price. The problem is: old machineries continue to be used at the cost of the time it takes to implement projects.
While most tunnel designers in India are from overseas and aware of the NATM and latest tunnelling technologies, and they specify the use of those technologies in tunnelling contracts, contractors use very old equipment, which breaks down frequently, causes unnecessary vibration and slows down the implementation of projects, observes Dr Mandal.
“We have no shortfall of machinery but instead we need to specify that contractors buy new machinery for tunnelling projects. That would boost the production rate. Clients for tunnelling construction must include more stringent clauses in contracts.” he adds
What Would It Take To Indigenise Tunnelling Equipment?
“Indigenising the production of tunnelling equipment needs a change in the mindset of those planning roadways and railways through mountainous regions in the sense that India is still not comfortable with the concept of tunnelling; we have a mindset that tunnelling is very expensive, which isn’t really the case in the long-term,” points out Col Deepak Patil, General Manager (Project), Silkyara Tunnel, National Highways & Infrastructure Development Corporation. ..
“Austria, for example, has straight roads in mountainous regions that go through mountains instead of over or around; going over destroys slopes and makes roads longer to traverse. If we start constructing more tunnels, we would increase our need for tunnelling machines and if this information were imparted to the construction equipment industry, there would be a greater interest in indigenising these machines.” he adds.
“The Government should bring all the relevant PSUs/construction agencies, contractors and domestic and overseas manufacturers on one platform to forecast the prospective plan for the next 30 years. This would help manufacturers fathom the quantum of workload. Making equipment in-house using knock-down kits or by raising a complete new ecosystem is the need of the hour.”
Safe Tunnelling: Precautionary tips
When using tunnel boring machines (TBMs) in cities, surface precautions and monitoring are essential to ensure the safety of existing structures and their occupants.
“While using the TBM for the Jama Masjid metro station to Delhi Gate metro station of the CC05 (heritage line) of DMRC Phase 3, the contractor had to erect vertical supports in all the structures in the old Daryaganj area, and even evacuated a large number of inhabitants of an above ground building in a phased manner as a precautionary measure,” points out Saini. “After tunnelling, the contractor also repaired and restored their houses for minor visible cracks.”
Further, when the TBM constructing the CC27 line of DMRC Phase 3 was approaching Munirka Metro station from the Vasant Vihar side, it had to negotiate a curve of 250 m radius in rocky strata, situated on an outer ring road flyover.As a precautionary measure, the flyover settlement was monitored by installing optical targets installed at critical locations adjoining the piles and pile cap of the nearby piers, he adds.
When tunnelling with TBMs, accurate probe drilling and grouting are essential to avoid unforeseen collapses and conical shaped formation of the mixed ground above, continues Saini.
“Also, the replacement of the cutter disk damaged owing to wear and tear [during mining] is a regular feature. This is done while performing cutter head interventions in hard rock and sometimes requires expert workers to be sent into the chambers. Proper care is very essential during this activity. Creating an inhouse workshop for the repair of the disk helps minimise costs and ensures disks are available in time.” he says
Watch out for tunnelling stalling events
- Sudden ingress of heavy water: “The sudden ingress of heavy water while executing tunnelling work, particularly in the Himalayan region, is a real challenge that can stall work for days,” Ranvir Singh, Manager (Projects) and Contracts Management Expert (Tunnelling), PEMS Engineering Consultants, based on his tunnelling experience in the Udhampur-Srinagar-Baramulla Rail Link (USBRL) project.“Also, heavy slides/slope circles on the surface are unpredictable but invariably happen. They can even necessitate changes to the approach road or track alignment, which, in turn, can delay projects. We saw a lot of natural movement/sinking of area when we were working on the USBRL, which is why we need to speed up work wherever possible to cope with these delays that occur.”
- Sudden changes in geology: “Sudden changes in geology necessitate a change in the cutter head in the tunnel boring machine (TBM), which is difficult and time-consuming because TBMs come with standard cutter heads,” notes Col Deepak Patil, General Manager (Project), Silkyara Tunnel, National Highways & Infrastructure Development Corporation.“Also, sometimes, the rock is unable to take on its own load and squeezes the TBM, causing the machine to get stuck and a huge loss of time and money. Now double-shielded TBMs are available but still not very appropriate in the Himalayas.”