Tunnelling Advancements in INDIA

Tunnels have played a vital role in the evolution and sustenance of mankind through the ages. History has seen the evolution of tunnelling starting with cave formation, for water management, underground transportation, mineral extraction and for warfare purposes. Initially hand dug with crude tools like chisels, hammers, spades and shovels, the civil engineering tunnelling technology has seen progress in leaps and bounds. The ever increasing needs of the modern human race have driven the tunnelling technology to its pinnacle. This is being realized through rapid advancements in terms of geological and hydro-geological engineering, tunnel design, capacity, construction methods and speed and maintenance during operations. Safety during construction and operations is getting integrated in all aspects through conscious and educated decisions.

HCC in India's tunnelling history

India's tunnelling history goes hand-in-hand with that of HCC. HCC's long-standing expertise in tunnelling dates back to the inception of the company in 1926. Undertaking its first contract in 1926, HCC constructed the Bhor Ghat Tunnel on the Mumbai-Pune Railway line in 1928. Evolving since then, HCC never looked back. 

With its unflinching determination, HCC has matured its understanding of tunnelling, starting with classical methods, the elementary drill and blast method, the cut and cover method, the New Austrian Tunnelling Method (NATM), shields and tunnel boring machines (TBMs) and special methods. With a proud contribution of one-fourth of the nation's hydro power construction, HCC's 365 km of tunnelling experience can be divided as follows - 3% with the cut and cover method, 69% with the drill and blast method, 24% with the TBM and around 4% with the NATM method.

Dealing with variegated geology

Constructing tunnels through various geological formations in India and its neighbouring countries, HCC has a great deal of experience in dealing with proportionate and occasionally disproportionate magnitudes of uncertainties and risks. This includes tunnelling in soils that are relatively younger and assorted geological formations in the Himalayan region, recent and Pleistocene area, Deccan Trap, Gondwana, Vindhwan, Alluviam areas and Pre-Cambrian geologies. The risk constituted construction in almost all the seismic zones of India.

Encounters with the Himalayan Mountains

Tunnelling through fragile, weak and jointed rock masses of the Himalayas is often challenging for planners, designers, engineers, geologists and, most importantly, construction contractors. This is primarily due to high overburden, thickly vegetated and inaccessible terrain, varied rock formations, presence of small and big shear zones/thrusts and associated hydrological challenges. Tunnelling in such regions invites multiple, often unforeseen problems such as face collapse, chimney formation, water-inrush, hot water springs, gas explosion, squeezing and so on. Dealing with such issues necessitates responsive and 'on the toes' engineering and construction, often requiring sleepless vigil and presence of mind. To alleviate and surmount such challenges, HCC in its bloodline has built sound construction practices that include detailed geological explorations, state-of-the-art designs, adaptable tunnelling practices, in-depth knowledge of monitoring and feedback systems and mechanisms with an inbuilt culture for safety.

First successful TBM in Himalayan region - a world record: Undertaking one of the longest constructed tunnels in India (23.65 km length and 6 m dia) with a maximum overburden of 1,470 m, HCC utilised a double-shield TBM for its Kishanganga hydropower project. Completing 14.75 km of tunnel, HCC created a world record of being the first successful TBM operations in the Himalayan region in a record time of 24 months, with an average monthly progress of 406 m. While dealing with adverse geologies, HCC also created a national record of the highest monthly progress in tunnelling of 816 m in the month of October 2013. The remaining length of 8.89 km of the tunnel was constructed using the drill and blast method.

Building nation's longest transportation tunnel: Entrusted with the responsibility of building the longest railway tunnel, Pir Panjal (J&K), HCC utilised the NATM method for dealing with rugged terrains of the Pir Panjal region, connecting Bichleri Valley on the south side and the Kashmir Valley on the north side. In this challenging and marvellous project in the history of Indian Cilvil Engineering, many geological surprises and challenges were faced in the relatively younger Himalayan geology. This state-of-the-art tunnel of 11.125 km is 100% waterproof and equipped with the latest fire fighting systems. As an accolade for completing this project, HCC was awarded two more projects along the same alignment.

Serving urban transport

Tunnelling in urban grounds is complex and challenging, often due to construction in soft soils, existing urban infrastructure, high-rise buildings, existing public utilities and, most importantly, safety for human life. While meeting such challenges of developing the nation, HCC has built India's first Metro rail project at Kolkata, wherein 6.47 km of stretch was built including four underground stations.

HCC has been involved in the construction of six underground sections, which are a part of the strategic plan of Delhi Metro Rail Corporation. A total of 23 km of tunnels are constructed in six packages with 12 underground stations.

HCC is constructing 4.049 km underground twin tunnels on EPC basis for Mumbai Metro Line III starting from the southern end of CST Station to the southern end of Mumbai Central Station including the four underground stations - CST, Kalbadevi, Girgaon and Grant Road. While the CST station is being constructed by the traditional cut and cover method, the Kalbadevi, Girgaon & Grant Road stations is constructed by NATM.

Meeting dimensional challenges

Largest diameter TBM deployed by HCC: For constructing a 19.2 km long tunnel for Pula Subbaiah Veligonda irrigation channel in Andhra Pradesh, HCC deployed a 10 m diameter double-shield TBM of Robbins make. The continuous lining behind the machine consists of 300 mm thick concrete segments in 6+1 arrangement, making the finished tunnel diameter 9.2 m. The tunnel path was located in sedimentary rock with a number of faults and folds with some ground water. A probe drill mounted on the machine allowed for verification of the geology 30 m ahead of the TBM. A strict programme of probe drilling combined with adequate ground stabilisation allowed the TBM to advance through difficult sections of rock.

Smallest and largest diameter tunnels: The smallest diameter tunnel constructed by HCC was for Brihanmumbai Municipal Corporation. It was a 2.74 km long sewage tunnel with a finished diameter of 2.5 m, constructed using a shield TBM and lined with precast concrete segments. Tunnelling challenges included massive and weathered basalt as well as the groundwater level along the tunnel alignment. A Herrenknecht hard rock TBM of 3.065 m diameter with integral automatic grout injection system was used for the construction of this tunnel. For the first time in India, a shielded hard rock TBM and the gasketed linings were used in this project.

On the other hand, the largest diameter tunnel constructed by HCC was for the Nathpa Jhakri hydroelectric power project. The 1,530 MW project boasts of the largest and longest Head Race Tunnel, the largest desilting chambers, the deepest and the largest surge shaft, and the largest underground power complex.

The way ahead

With India's strategic infrastructure development plans on their way to implementation, there is great scope for tunnelling in India, especially for developing urban infrastructure, underground rail and road networks, transportation in mountainous regions and so on. Refinements in designing capabilities and the ability to utilise instrumentation data will enhance our ability to foresee uncertainties and risk. In order to better access risk and uncertainties, detailed geological explorations will have to take deeper roots. A greater level of mechanisation of tunnels will reduce construction time and help early revenue generation.

Article courtesy: HCC

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