A Terratec rock EPBM has completed a sharp 87m radius curve for the Mumbai Sewage Disposal Project.
The 3.14m diameter TBM S116 achieved the engineering feat on the 4.6km-long Priority Sewer Tunnel-Phase 2, between Goregaon Pumping Station and New Malad IPS. Terratec says the achievement sets new standards for urban tunnelling in constrained environments.
The project posed a significant engineering challenge: to drive a tunnel through a sharp 90-degree curve beneath a busy road junction – without the use of a shaft.
The TBM had to maintain millimetre precision while navigating just 2.3m of clearance between active metro foundation pillars, all during live train operations. It also passed through a section with minimal overburden, encountering highly variable ground conditions, including 95MPa basalt, large boulders, and mixed soils.
The TBM also excavated approximately 500m directly beneath a creek and mangrove wetland, managing the substantial risks associated with tunnelling through an environmentally sensitive area with very low overburden.
Terratec says the achievement was made possible by deploying a purpose-built spherical articulation TBM, supported by a suite of innovative engineering solutions tailored specifically for the project.
The team introduced a dual-segment lining system – 660mm rings for the sharp-radius curve and 1000mm segments for the straight sections. The excavation of the tight-radius section marks a first for tunnelling projects in India. Key modifications to the TBM included cutter disc adjustments to enable controlled overcutting, customised rolling stock to accommodate reduced clearances, and a conveyor system engineered to navigate the sharp curvature.
The tight-radius solution offered significant advantages over conventional methods by eliminating the need for Shaft S10 at a congested road intersection near a shopping mall and metro station. This approach prevented major traffic disruptions and resulted in substantial savings in both construction time and cost.
As the smallest segmental EPBM in its class operating in India, the machine was designed to operate within extremely confined internal dimensions. These constraints, although expected, were carefully addressed through detailed planning, continuous monitoring, and precise machine steering. Terratec says this controlled approach proved especially critical when navigating the hard geological formations in the curve section.
TBM S116 shares the same design as its sister machine, TBM S80, which previously worked on the MSDP Stage-II Priority Works and is now tunnelling for the Mithi River Water Quality Improvement project. Both TBMs have maintained impressive productivity, averaging 300 rings – or approximately 360m – of tunnel advancement per month.
The Mumbai Priority Sewer Tunnel is a critical component of the city’s wastewater management upgrade, designed to significantly reduce pollution in the Mithi and Oshiwara rivers while enabling advanced water recycling processes.
