DMRC tunnel beneath Red Line boosts Magenta Line Phase-IV

DMRC tunnel beneath Red Line at Pulbangash is being highlighted as a standout engineering milestone on the Magenta Line Phase-IV extension.

This is reported by the railway transport news portal Railway Supply.

The underground tunnel was completed beneath the operational corridor without any break in service, as detailed in a recent press release from the Delhi Metro Rail Corporation, with advanced ground treatment and continuous real-time monitoring used to protect the Red Line structure above.

The Delhi Metro Rail Corporation (DMRC) is once again showing how it can handle complex construction in dense urban conditions, this time by finishing sensitive tunnel works under Delhi’s busy Red Line without a single day of disruption.

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The project forms part of the Janakpuri West–RK Ashram Marg Magenta Line extension, one of the main corridors being advanced under Phase-4 of the Delhi Metro expansion and tied directly to the wider urban mobility network.

The new underground link sits between Pulbangash and Sadar Bazar stations and runs directly below the elevated Red Line viaduct. Trains on this stretch operate throughout the day and together carry more than seven lakh passengers daily. The difficulty was not only working beneath an active metro route: the viaduct is founded on open foundations and includes a balanced cantilever span, so tunnelling beneath it was treated as a high-risk task that demanded careful planning, strong engineering controls and continuous supervision.

DMRC tunnel beneath Red Line: engineering challenges and safety approach

To keep the operational metro line above unaffected, DMRC’s engineering team put in place a broad package of structural safety measures. Their approach combined recognised international tunnelling practices, strict monitoring procedures and ground-strengthening that was specifically tailored to conditions at Pulbangash. This framework allowed the tunnel construction beneath the operational Red Line at Pulbangash to move ahead without compromising passenger safety or day-to-day service reliability.

TAM grouting and ground strengthening at Pulbangash

One of the most important interventions for the Pulbangash–Sadar Bazar underground tunnel section was stabilising the soil around the pier supporting the Red Line viaduct. For this, engineers turned to Tube-a-Manchette (TAM) grouting, an internationally recognised deep ground-improvement technique frequently used to reinforce soil before sensitive tunnelling work.

The ground treatment followed several key steps:

• drilling 180 TAM boreholes around the structurally critical pier;
• injecting high-strength cement grout into these boreholes to fill voids, improve soil stability and increase load-bearing capacity;
• preventing soil settlement during the tunnel boring process by forming a stiff, reinforced zone beneath the operational viaduct.

As a result, the TAM grouting programme created a uniform, stable ground mass capable of safely accommodating tunnelling beneath the operational viaduct of the Red Line and supporting the overall safety concept for the Magenta Line Phase-IV extension.

Real-time monitoring and advanced instrumentation by DMRC

Because tunnel excavation was taking place beneath an elevated, balanced cantilever structure, DMRC also deployed an extensive suite of real-time monitoring and advanced instruments around the construction area. The aim was to follow even the smallest ground or structural movements while work progressed on the DMRC tunnel beneath Red Line infrastructure.

The monitoring setup included:

• Surface Settlement Markers to track vertical ground displacement at the surface;
• Deep Inclinometers to detect subsurface lateral movement;
• Building Settlement Points to watch for potential impacts on nearby structures;
• Pier Tilt Meters and Load Cells to observe how the Red Line pier behaved and how loads were distributed during construction;
• an Automatic Total Station (ATS) for continuous, high-precision tracking of structural positions.

Specialised personnel remained on site around the clock to interpret and validate the data coming from these instruments. Throughout the tunnel construction, all recorded values stayed within the defined safety limits, confirming that the mitigation measures were working as intended and that the viaduct above continued to operate safely for everyday passengers.

Magenta Line Phase-IV extension and progress at Pulbangash

With the down-line tunnel at Pulbangash now completed to these stringent safety and monitoring standards, work on the up-line tunnel is progressing under the same framework. The broader Phase-IV development of Delhi Metro, which includes the Janakpuri West–RK Ashram Marg Magenta Line extension, reflects DMRC’s strategic approach to reinforcing public transport connectivity across the Delhi-NCR region.

Today, the Magenta Line runs from Botanical Garden to Krishna Park Extension, covering approximately 40 km. Along the way it offers key interchange options at Janakpuri West, Hauz Khas and Botanical Garden, which makes it one of Delhi Metro’s busiest corridors and supports dense daily ridership. The ongoing Magenta Line Phase-IV extension is designed to build on this role by adding more direct connections and reducing reliance on road-based travel.

Strengthening Delhi’s metro network and urban mobility

Delhi Metro’s operational network currently extends to 394.448 km and 289 stations, confirming its place among the world’s largest metro systems — a point also underlined by Railway Supply in its coverage of the network’s growth. The continued development of corridors like the Magenta Line under Phase-4 shows DMRC’s focus on improving last-mile connectivity, easing congestion and supporting the city’s sustainability objectives.

By completing the DMRC tunnel beneath Red Line infrastructure at Pulbangash without any disruption to services, the corporation has demonstrated that it can manage highly sensitive engineering tasks while maintaining day-to-day operations. This ability to expand the system without interrupting service remains central to Delhi Metro’s role in meeting the region’s growing mobility needs.

Conclusion: a benchmark for urban tunnelling in India

The successful construction of the tunnel beneath the operational Red Line marks an important milestone in India’s urban engineering capabilities.

By combining advanced tunnelling technology, targeted ground strengthening using Tube-a-Manchette TAM grouting and a robust real-time monitoring regime, DMRC has shown that even high-risk underground works can be carried out safely under live infrastructure.

As the Magenta Line Phase-IV extension progresses, this project stands as a reference point for future complex tunnelling beneath existing metro lines while enhancing daily mobility for millions of passengers.

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