How Delhi Metro dug an underground tunnel beneath Red Line — without halting services
The Delhi Metro Rail Corporation (DMRC) Sunday said that it has finished tunnelling the down-line section of the Janakpuri West-RK Ashram Marg extension of the Magenta Line — passing under the Red Line viaduct
A Tunnel Boring Machine (TBM) passed under the Red Line viaduct between Pulbangash and Sadar Bazar, while trains continued to operate normally above. (Express Photo)
At Pulbangash in North Delhi, engineers of the Delhi Metro have completed a rare and complex construction task: building an underground tunnel directly below an operational elevated Metro line, without halting train services even for a day.
The Delhi Metro Rail Corporation (DMRC) Sunday said that it has finished tunnelling the down-line section of the Janakpuri West-RK Ashram Marg extension of the Magenta Line.
A Tunnel Boring Machine (TBM) passed under the Red Line viaduct between Pulbangash and Sadar Bazar, while trains continued to operate normally above. Work on the up-line tunnel is currently in progress.
According to officials, this location posed unusual engineering challenges because the Red Line’s elevated viaduct rests on open foundations and includes a balanced cantilever span.
Such structures are sensitive to even small shifts in the ground.
Any movement during tunnelling could have affected the pier that supports the running line, which carries about 7 lakh passengers every day. DMRC said this made it essential to take “extraordinary engineering precautions”.
To ensure safety, the first step involved strengthening the ground around the Red Line pier. Engineers implemented a grouting programme known as TAM (Tube-a-Manchette) grouting. As part of this method, they drilled 180 TAM boreholes around the pier and then carried out high-strength cement grouting.
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In simpler terms, this process fills underground gaps with a cement mixture to stabilise the soil, increase its load-bearing capacity and eliminate any possibility of settlement when the TBM moves below.
Alongside ground strengthening, DMRC deployed what it described as “world-class instrumentation” to monitor every aspect of the site in real time.
Devices such as Surface Settlement Markers, Building Settlement Points, Deep Inclinometers, Pier Tilt Meters, Load Cells and an Automatic Total Station were used to track ground movement, pier behaviour and building safety.
Specialised personnel monitored these readings round the clock. According to DMRC, all parameters remained well within permissible limits throughout the tunnelling.
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Officials said the safe completion of the down-line tunnel marks an important engineering achievement in the ongoing Phase IV expansion, especially because any disruption on the Red Line would have caused significant inconvenience to commuters.
Devansh Mittal is a Correspondent at The Indian Express, based in the New Delhi City bureau. He reports on urban policy, civic governance, and infrastructure in the National Capital Region, with a growing focus on housing, land policy, transport, and the disruption economy and its social implications.
Professional Background
Education: He studied Political Science at Ashoka University.
Core Beats: His reporting focuses on policy and governance in the National Capital Region, one of the largest urban agglomerations in the world. He covers housing and land policy, municipal governance, urban transport, and the interface between infrastructure, regulation, and everyday life in the city.
Recent Notable Work
His recent reporting includes in-depth examinations of urban policy and its on-ground consequences:
An investigation into subvention-linked home loans that documented how homebuyers were drawn into under-construction projects through a “builder–bank” nexus, often leaving them financially exposed when delivery stalled.
A detailed report on why Delhi’s land-pooling policy has remained stalled since 2007, tracing how fragmented land ownership, policy design flaws, and mistrust among stakeholders have kept one of the capital’s flagship urban reforms in limbo.
A reported piece examining the collapse of an electric mobility startup and what it meant for women drivers dependent on the platform for livelihoods.
Reporting Approach
Devansh’s work combines on-ground reporting with analysis of government data, court records, and academic research. He regularly reports from neighbourhoods, government offices, and courtrooms to explain how decisions on housing, transport, and the disruption economy shape everyday life in the city.
Contact
X (Twitter): @devanshmittal_
Email: devansh.mittal@expressindia.com ... Read More