Kolkata, July 10: For months, the only sign of its presence was a faint tremor logged on a monitoring screen somewhere in Kidderpore. Today, twenty-odd metres beneath the city, that tremor stopped mattering the cutter head broke through a specially built structural wall, and tunnel boring machine “Durga” (S-1410A) rolled into the shell of the still-unfinished Victoria Memorial station. It is a milestone the Kolkata Metro’s Purple Line Line 3 has been building towards for exactly a year.
A year ago to the day, Durga had set off from a launching shaft dug inside the grounds of St. Thomas’ Boys’ School in Kidderpore. What has followed since is a slow, deliberate crawl through some of the city’s most sensitive ground and today marks the end of its first leg.
The project, in brief
The stretch Durga is boring through belongs to Package UG1, a ₹2,447 crore underground contract awarded to Larsen & Toubro (L&T) and overseen by Rail Vikas Nigam Limited (RVNL). It covers 5.05 km between Mominpur and Esplanade the section where the Purple Line has to leave its elevated viaduct behind and dive underground to reach the heart of the city.
Durga is an Earth Pressure Balancing (EPB) machine, a design chosen specifically to cope with Kolkata’s soft, waterlogged soil. It runs 95 to 100 metres long, carries an outer diameter of 6.63 metres, and weighs close to 600 tonnes. Its components were built by Herrenknecht in Germany and assembled at a facility in Tamil Nadu, part of the project’s “Make in India” component. Following a long-standing tradition of naming tunnel-boring machines after women in honour of the patron figures of miners this one was named for the city it works in: Kolkata, the land of Maa Durga. Its twin, boring the parallel downline tunnel, is named Divya.
A year underground, step by step
| Milestone | Date | Detail |
|---|---|---|
| Launch | July 10, 2025 | Boring begins from the Kidderpore shaft |
| RCTC crossing | January 2026 | Machine passes safely beneath the Royal Calcutta Turf Club grounds |
| Phase 1 breakthrough | July 10, 2026 | Durga enters Victoria Memorial station |
| Phase 2 (planned) | Late 2026 | Victoria to Park Street, approximately 900 metres |
Since Victoria station’s box structure is still under construction, Durga cannot simply pass through — it will be repositioned and relaunched from the same site for its second leg toward Park Street.
Getting here meant threading a tunnel beneath the Royal Calcutta Turf Club’s century-old grandstands without so much as a crack showing. Engineers had mounted automated total stations and 3D tilt sensors across the heritage structures, watching for movement measured in single-digit millimetres, before the machine was allowed to slow to a crawl and pass beneath.
Where its twin, Divya, stands
Roughly a month after Durga set off, its identical twin Divya (S-1411A) left the same shaft to bore the parallel downline tunnel. It has already cleared the Royal Calcutta Turf Club stretch and is currently working its way beneath the Maidan. Project engineers expect Divya to reach the Victoria Memorial site by late August.
Digging under a heritage skyline
Running tunnel machinery beneath a 150-year-old marble monument is not something engineers take lightly, and the safeguards built into this stretch reflect that:
- Foam and polymer additives are injected at the cutter head to turn excavated soil into a controlled paste, balancing the pressure of the ground above so nothing settles.
- Sensors fixed to heritage structures the Victoria Memorial, old buildings in Kidderpore, the RCTC stands flag any movement beyond a few millimetres instantly.
- Beneath the most sensitive stretches, the machine’s advance is deliberately slowed to just a few metres a day to keep ground vibration to a minimum.
- Cement grout is pumped in at high pressure through the tail shield the moment the machine moves forward, locking each concrete ring firmly against the surrounding soil.
Esplanade: where three lines will finally meet
The tunnel Durga and Divya are boring eventually leads to Esplanade, which is being built as Kolkata’s largest interchange — a four-level underground station box where the Blue Line, Green Line, and this Purple Line will converge. Part of the B.C. Roy Market had to be cleared, following Defence Ministry approval, to make room for the terminal station’s footprint. Once complete, commuters will be able to switch lines through connected subways without stepping outside the ticketed zone.
What lies ahead
The Purple Line’s rollout runs in three broad phases. The Joka-to-Majerhat elevated stretch is already carrying passengers. The underground push from Majerhat to Esplanade — the one Durga and Divya are working on — is targeted for completion by the end of 2026, with the remaining cut-and-cover stretch from Park Street to Esplanade expected to wrap up by late 2027. Full commercial operation across the Joka–Esplanade corridor is projected for 2028–29, alongside a separate ₹378 crore land acquisition push for a further extension to IIM Calcutta and Diamond Park.
Why it matters
Once finished, this corridor will cut travel time between south Kolkata and the city centre considerably, ease road traffic along some of the most congested stretches in the city, and give commuters a three-line interchange at Esplanade that Kolkata has never had before. Property markets in Alipore, Behala, and Garden Reach have already begun responding to the promise of that connectivity — a fairly reliable sign of how much the city is banking on this line.
Today’s breakthrough is, in the end, just one wall out of many still to come. But for a project that has had to negotiate racecourses, colonial-era grandstands, and a 150-year-old marble memorial without disturbing a single brick, breaking through cleanly counts for something.
(Sources: Rail Vikas Nigam Limited, Larsen & Toubro, Times of India, Metro Rail News)