A Terratec 3.85m-diameter rock slurry TBM has completed excavation of the 5.85km Priority Sewer Tunnel 1 (PST-1) for the Mumbai Sewage Disposal Project (MSDP) Stage II.
J Kumar–MEPL JV launched the TBM from Malad Shaft S07 Pumping Station in January 2024 and it made its final breakthrough on October 9 at Don Bosco Junction, near Borivali West.
The first 1.63km section to Malad West was completed in August 2024, and the TBM then bored the second section of 4.22km. It passed the 4.5km mark of the total drive in January this year.
The TBM advanced beneath densely built-up areas of Mumbai, passing under busy roads, buried utilities and residential and commercial buildings, as well as through environmentally sensitive areas. The alignment traversed weathered and fresh breccia and basalt, with the machine achieving up to 18 rings per day in fresh rock. Continuous monitoring of alignment and ground movement minimised surface settlement and safeguarded surrounding infrastructure.
Among the smallest machines of its kind in India, the TBM controls face pressure with a slurry system, and excavated material is pumped to the surface through the Terratec Slurry Transportation System for separation at the Terratec Slurry Treatment Plant.
The machine features 23 replaceable 381mm disc cutters, a high-speed hydraulic main drive turning the cutterhead at up to eight revolutions per minute, a shield-integrated man lock, and an active articulation system for curves down to a 250m radius.
The tunnel is lined with 5+1 universal reinforced concrete segments, 200mm thick and 1,200mm wide, giving a finished internal diameter of 3.2m.
As well as providing the 3.85m-diameter rock slurry TBM for PST-1, Terratec also supplied a 3.14m-diameter rock EPB TBM for the 4.7km PST-2. On PST-2, the EPB machine set a first for India in 2025 by negotiating an 87m radius curve beneath a busy road junction without an intermediate shaft. It is now being disassembled.
Once in operation, PST-1 will be a key part of Mumbai’s upgraded wastewater network, carrying sewage to downstream treatment facilities and allowing ageing pumping stations to be decommissioned. The wider programme is expected to recycle 2,464 million litres of sewage per day, reduce the discharge of untreated wastewater into local waterways and the Arabian Sea, and support the rejuvenation of the Mithi and Oshiwara rivers.
