The Joka–Esplanade Metro Corridor (Purple Line) is a major metro infrastructure project in Kolkata, comprising 12 stations and connecting Joka with Esplanade. The corridor has a total length of approximately 14km, of which the 7.74-km Joka–Majerhat section is operational. The remaining 6.26-km Majerhat–Esplanade section is under construction. It includes an underground stretch in the central part of Kolkata, where twin tunnels are being constructed beneath a densely built-up urban environment. The underground portion runs from Kidderpore to Park Street, with the remaining part toward Esplanade being constructed by cut-and-cover methodology.

Two new EPB Shields (Earth Pressure Balance), known as “Durga” and “Divya”, are being used for the twin-tube tunnelling works between Kidderpore and Park Street. The machines have an outer diameter of approximately 6.63m and are engineered for Kolkata's geotechnical profile, with features tailored to silty clay, sand and high groundwater conditions. Each machine, assembled at Herrenknecht's Chennai factory, is approximately 95–100m long and weighs approximately 600 tonnes.

The first TBM, "Durga", commenced tunnelling from Kidderpore in mid-2025. The second TBM, "Divya", followed from the same launching shaft in autumn 2025.
The completed tunnel has an inner diameter of approximately 5.80m and is lined with precast concrete segments.