Mumbai Sewer Tunnel Sets Record with 87m Curve

A significant engineering achievement was recorded in India’s tunnelling sector with the successful excavation of a tight 87-meter radius curve using the 3.14-meter diameter Rock EPBM (TBM S116). The milestone occurred on the 4.6-kilometer Priority Sewer Tunnel—Phase 2, connecting Goregaon Pumping Station to New Malad IPS. This section is part of the broader Mumbai Sewage Disposal Project aimed at modernizing the city’s wastewater infrastructure.

Navigating this curvature without a launch shaft posed complex challenges. The tunnel alignment required precision beneath a congested urban junction, with only 2.3 meters of clearance between operating metro foundation pillars. Adding to the complexity, the TBM passed beneath an environmentally sensitive area, including a creek and mangrove wetland, with minimal overburden and mixed geology featuring hard basalt and loose soils.

To meet these conditions, the TBM deployed possessed a spherical articulation and was specifically designed for confined environments. Engineering solutions included the use of a dual-segment lining system, featuring 660mm rings through the curve and 1000mm segments on straight sections. The TBM was further modified to allow overcutting via customized cutter discs and was paired with rolling stock and conveyors suited for tight-radius operation.

This strategy eliminated the need for Shaft S10 at a critical intersection, avoiding major traffic disruptions and resulting in reduced construction time and cost. The machine maintained high productivity throughout, averaging 300 segment rings in about 360 meters of tunnel per month.

The tunnel forms a key part of Mumbai’s ongoing efforts to improve river water quality and wastewater treatment. The described precision-based approach highlights the role of tailored tunnelling solutions in delivering critical urban infrastructure under spatial and environmental constraints.