Construction of metro tunnels in the country is still at a nascent stage. So far, the Delhi Metro Rail Corporation (DMRC) has constructed 750 km of metro corridors, of which 250 km is underground. Overall, 1,050 km of metro corridor stretches are under construction across the country. Of this, 300 km of network length is underground. These stretches are expected to be completed in the next four-five years.
At a recent conference organised by India Infrastructure, Daljeet Singh, director, DMRC, discussed the corporation’s experience, methods deployed for tunnel construction, noteworthy initiatives and the impact of COVID-19 on project delivery…
DMRC: Experience so far, pain points and notable achievements
Delhi’s geology is a complex superset of silts, clays, rocks and high ground water tables. In its 18 years of tunnelling, the DMRC has handled a gamut of issues –hidden wells, unknown drainage lines, unexpected rock encounters, sudden ground collapses, unstable soil strata, etc. Further, as infrastructure/utility works are being overseen by multiple agencies, infrastructural integration is one of the major concerns that remains to be addressed. While the utmost emphasis is placed on the technological aspects of tunnelling, the planning aspect often takes a back seat. However, things have started improving, with deployment of advanced surveying solutions during the initial alignment review (for example, by using drone surveys), advanced investigatory solutions during preliminary investigations (surface utility engineering and pilot tunnelling), implementing a meticulous data archival strategy to create a future data bank, etc. With respect to data storage, the DMRC has taken a huge leap with 100 per cent digitalisation of its records for future reference.
Further, the DMRC has also taken steps to ensure coordinated project planning. For example, most of the alignment of the R.K. Ashram Marg-Majlis Park corridor and the Tughlakabad-Saket corridor of Phase IV of the Delhi metro project was along the right of way owned by the public works department (PWD). Further, the PWD had planned the construction of flyovers along the same alignment. Since this would not have been possible after the completion of DMRC works, it was decided to integrate the structures, thus ensuring better augmentation of the public transit system. Similar coordination was successfully accomplished at NabiKarim as well. Once completed, it will be a state-of-the-art public utility hub with an underground integrated interchange metro station below a fully automated parking with a capacity of 3,200 cars along with 25,000 square metres of core commercial space.
With respect to the various methods of tunnelling, tunnel boring machines (TBMs) dominate tunnel construction in the metro rail sector with most of the completed and under-construction tunnels using this technique in combination with other techniques. Tunnelling through TBMs is one of the most advanced, fastest and safest modes of tunnelling. Besides TBMs, the other methods that are used for metro rail tunnels are cut and cover, the New Austrian Tunnelling Method and the box pushing method.
Fallout of COVID-19
The infrastructure sector has been one of the worst affected by the COVID-19 outbreak. Being a highly capital-intensive sector with major projects being funded by government agencies, the sector has been severely impacted as the government’s focus has now shifted towards the health and rehabilitation of the affected masses. With respect to metro projects, the challenge is far bigger as most of the workforce deployed is specialised migrant labour. Most of them have returned to their native places, as convincing them to stay at construction sites has become tougher.
Even though the government has permitted recommencement of construction activities, delays in and irregular delivery of raw materials and finished products has made it extremely difficult to plan activities at the site. A steep rise in the cost of many resources, including manpower, due to their limited availability is another problem. Meanwhile, ensuring the safety of workers stationed on site has become increasingly challenging.
Key learnings and the road ahead
Going forward, the outlook for the metro tunnel development market is promising and will be driven by the government’s focus on infrastructure development. While a lot has been achieved in terms of completed and upcoming capacity, the execution of metro rail projects is still marred by a number of challenges. In this regard, early land acquisition and tree cutting permissions goes a long way in timely completion of construction works. A well-coordinated planning process at the initial stage can also make a big difference later. In addition, utility and geotechnical investigation works need to be given much greater attention.
The future of metro rail development in the country rests on the development of integrated solutions. Therefore, close coordination with all agencies holds the key to success. Recording and documentation of all the experiences and archiving data too holds immense importance for future projects.