In a stunning display of engineering precision, the Delhi Metro Rail Corporation (DMRC) has successfully constructed a full-scale underground tunnel directly beneath the busy, operational Red Line, all without halting train services for a single day. The remarkable project, connecting Pulbangash and Sadar Bazar, was executed while thousands of daily commuters travelled undisturbed on the elevated tracks just metres above the massive tunnelling activity.
A Delicate Operation Under a Live Viaduct
The core challenge was the construction site itself: directly under an elevated metro viaduct supported by open foundations and a balanced cantilever span. This type of structure is extremely sensitive to any ground movement or vibrations. Engineers had to ensure that the immense forces and disturbances from tunnelling did not transfer any structural stress to the viaduct pillars above, which could have jeopardised safety and operations.
To navigate this, DMRC deployed a specialised Tunnel Boring Machine (TBM) calibrated to operate with controlled excavation pressure. The machine worked at precise torque and speed to minimise soil displacement. Crucially, it installed pre-cast tunnel rings simultaneously with excavation, providing immediate ground support and stabilising the area as it advanced.
Fortifying the Foundations with Advanced Techniques
Prior to and during tunnelling, a critical safety step was implemented to protect the Red Line's piers. Engineers used the advanced Tube-a-Manchette (TAM) grouting method. This involved drilling 180 TAM boreholes around the critical pier area and injecting a high-strength cement slurry deep into the soil.
This high-pressure grouting served a dual purpose: it bonded loose soil particles into a denser, more stable mass, and it filled any existing underground voids. The process created a reinforced, protective buffer around the viaduct's foundations, significantly boosting the ground's load-bearing capacity and shielding it from potential settlement caused by tunnelling.
Round-the-Clock Vigilance with Data-Driven Safety
The entire operation was underpinned by a sophisticated, real-time monitoring system. A network of sensors was installed to continuously track the slightest changes in soil displacement, vibration levels, pier tilt, and settlement patterns. This data provided an instant, live feed of the ground's response to the tunnelling work.
Dedicated technical teams analysed this data 24 hours a day, 7 days a week. Their constant vigilance allowed for immediate intervention if any parameter approached a safety threshold. This seamless coordination between the tunnelling engineers on site and the metro operations control room was vital to maintaining both construction safety and uninterrupted train schedules.
A New Benchmark for Urban Infrastructure
The successful completion of the down-line tunnel marks a significant milestone. Work on the parallel up-line tunnel is now progressing with the same rigorous protocols. Once finished, this new section will enhance connectivity for the upcoming Metro Phase projects in one of Delhi's most densely populated corridors.
This project, executed while Red Line services ran entirely without slowdowns or cancellations, sets a new global benchmark for urban infrastructure development. It proves that complex engineering challenges in congested, operationally sensitive city environments can be overcome with meticulous planning, cutting-edge technology, and unwavering focus on safety. The DMRC's achievement not only strengthens Delhi's metro network but also provides a replicable model for future infrastructure projects across India's metropolitan landscapes.
