Bored tunnels using Tunnel Boring Machines (TBMs) are the future for India?s urban and other infrastructure development initiatives.

The Robbins Company designed and manufactured the world?s first rock tunnel boring machine, shortly after the company?s founding by James Robbins in 1952. Robbins built the TBM for Mitry Constructors who were working on the Oahe Dam diversion project near Pierre, South Dakota, USA.

The Robbins Company also invented both the Main Beam and Double Shield TBMs. Robbins is best known for its very successful Main Beam TBMs, they are also pioneer in hard rock double shield machines. More specifically, the company has manufactured 50 Robbins double shields for 85 projects totalling over 550 km of tunnel.

TBM applications
TBM is mainly applied to urban subway tunnel, cross-river roadway or railway tunnel, sub-sea roadway or railway tunnel, urban municipal engineering tunnel, oil-gas pipeline tunnel, water tunnel, etc.

?TBMs are preferred in construction of tunnels in all types of geology with minimum disturbance/deterioration to environment. For example, metro rail projects in congested urban areas are difficult or rather unthinkable to construct without TBMs. The construction of tunnels for irrigation and hydro power project in difficult seismic conditions or under wildlife areas is also an example where construction using TBMs is a preferred method. Another useful utilisation is water, sewerage, sea-outfall, transport tunnels under sea, river, and water bodies, where it is much easier using TBM technology,? educates Manoj Garg, Managing Director, Herrenknecht India P Ltd. ?There can be different applications for the use of TBM like metros in the urban areas, irrigation tunnels , road tunnels, hydro power tunnels and utility tunnels ,? says Kapil Bhati, Managing Director, The Robbins Company India Ltd.

Rajeev Kumar, CEO, Friends Equipment, reaffirms, ?TBM is mainly applied to urban subway tunnel, cross-river roadway or railway tunnel, sub-sea roadway or railway tunnel, urban municipal engineering tunnel, oil-gas pipeline tunnel, water tunnel, etc.? India?s infrastructure initiatives encompass the entire gamut of the above applications. As a result, TBMs are being preferred for speedy execution of tunnels in many projects spread across the Himalayas, metro cities, water management, road transport, Railways and sub aqueous tunnels.

Complexities in TBM designs
Geological profile, terrain conditions, purpose, length of and size of tunnel are primary considerations for designing a TBM which is an application and many a time, project specific equipment. It comprises suitable cutter head supported by a diverse set of sub-equipment which enables the completion of the tunnel to the required specifications, under a given set of operating conditions.

Through experience, many types of TBMs are now available from various suppliers. However, it must be noted that every tunnelling work is unique, thereby requiring new innovations, systems and extra ordinary engineering inputs in every new TBM supplied by a manufacturer.

Challenges galore
Geo-technical and hydro geological uncertainties are the most significant challenge for TBM operations because despite detailed investigations prior to conceptualisation, the available data at its best can only be termed as preliminary and actual conditions encountered are highly unpredictable. Such situations may even lead to trapping of a TBM. Most of the times, bypass or diversion tunnels have to be made to release the TBM and in a worst case scenario, the equipment may have to be abandoned. Bhati relates to such operational challenges, ?There have been many challenges related to the operations of a TBM. One of the major challenges is dealing with different geologies; launching of the TBM. From the contractors point of view, arranging land, utility diversions and taking permission from different agencies for diversions is also a challenge. Traffic management is also considered to be one of the biggest challenges which a contractor has to encounter in constructing these types of projects.?

Other than that specific to India, most manufacturers are looking at changes in government policy.

?The government?s Make In India programme is defeated by the fact that imported TBMs are cheaper because of NIL rate of basic import duty applicable. Whereas local assembly of TBM attracts full duties and taxes. This tax anomaly is a major challenge for TBM manufacturers to invest and start TBM assembly in India. Herrenknecht is the only company which has invested in state-of-the-art TBM assembly plant in India and is suffering financially,? says Garg.

Kumar joins in, ?In many countries, there is a policy of free duty or preferential import for significant high-end equipment. We suggest that government support imported high-end equipment in a way of lowering their tax which is good for successful construction.?

Market vision
On a positive note, Garg visualises, ?Urbanisation, population growth, climate change, and a hunger for resources: The consequences of these mega trends are increasing demand in infrastructure projects. Tunnelling technology from Herrenknecht in operation around the world to build efficient tunnel infrastructure for metro projects, Railways, hydropower, as well as road projects has tremendous opportunity for this sector.? He adds,?With the massive expansion plan in India today, tunnels will become an integral part of Indian infrastructure, henceforth industry has tremendous opportunity in next five years.?

Kumar is also enthusiastic, ?India has a large population and a problem of urban traffic congestion, which strongly demands the development of urban underground rail transit. And due to India?s dense population, underground pipeline network construction is a basic requirement to guarantee the people?s livelihood. Thus, we think that there will be a big increase in the TBM demand in Indian market.?

Bhati shares the vision with facts and figures, ?Indian construction equipment industry looks promising especially with the Delhi Metro having in execution for Phase 3 which envisages adding 140 km of the network and the construction is in process at Bengaluru Phase I, Chennai Phase-I, Jaipur etc, and the metro is planned in other cities of the country like Bengaluru - Phase II, Chennai - Phase II, Lucknow, Hyderabad, Mumbai - Phase III, and Ahmedabad along with the road tunnels, highways, hydroelectric power projects that are underway and would require enormous number of equipment of all types which will bring boom in the construction industry and for the coming 10 years from now there would be vast pool of opportunities available for us to carter in all spheres.?

Conclusion
Although filled with numerous challenges, requiring experienced engineering skills and addressing uncertain geological domains, India needs to apply TBM tunnelling in big way, during its accelerated infrastructure development in the years to come. As such this industry is destined to boom.

TBM Advantages

• Protects on surface life
• Zero impact on aesthetics
• Minimum eco-disturbance
• Zero seismic vibrations
• Safe
• Adaptable to changing topography
• Tunnel length not a limitation
• Cost efficient

TBM Configurations & Applications

CONFIGURATION	APPLICATIONS IN DIFFERENT GEOLOGIES
Gripper	Hard and stable rock strata: granite, gneiss or basalt
Single Shield	Rock ground condition: Soft, brittle rock to hard basalt
Double Shield	All kind of stable and unstable rock and mix ground conditions
Mix Shield	Heterogeneous ground-sand gravel, high water permeability and water pressure.
Earth Pressure Bearing	Rocky to Soft ground conditions- clay, slit, loam, low water permeability and heavy over headburden which may shrink the tunnel size
Multi Mode	Convertible at pre-determined chainage for complex mix geology, high water pressure, e.g. 17 bar
Cross Over	Can work in combination of mixed soils and rock respectively