Tata Projects Ltd. achieved another milestone as TBM S81 B, nicknamed Kolli, made a breakthrough at Otteri station on Line 3 of the 116.1km Chennai Metro Phase 2. In July 2023, Tata Projects had deployed TBM Kolli on the south shaft of Ayanavaram Station on the 45.8km Line 3 (Mandharam station to Siruseri SIPCOT). After covering approximately 903m, TBM Kolli reached Otteri station within 13 months.

Kolli, a Terratec Earth Pressure Balance (EPB) machine, with a 06.61km reach, faced over 100 bore wells during excavation and had to navigate two sharp curves with radii of 220m and 280m to avoid disruptions.

Previously, TBM S18, after its first breakthrough in Pune Metro, passed its Factory Acceptance Test (FAT) in December 2022 before being deployed in Chennai Metro Phase 2. The current task involving TBM Kolli falls under Package TU-01, which was awarded to Tata Projects by Chennai Metro Rail Ltd. (CMRL) in May 2021 with a 42-month deadline. The total cost of the project is ?1999 crore.

Package TU-01 covers a 9km section on Line 3 of Chennai Metro Phase 2. TBM Kolli, along with six other TBMs under this package, is tasked with constructing a 9km twin tunnel (totalling 18km) from the TBM retrieval shaft near Venugopal (Line 5) to Kelly station (Line 3) and constructing diaphragm walls and entry and exit structures at four stations. So far, Tata Projects Ltd. has recorded six tunnel breakthroughs under Package TU-01.