Longest underground metro corridor of Bangalore Metro Phase 2 nearing completion

Bengaluru, India (Metro Rail Today): Over 95% of the civil works for the longest underground (UG) corridor in Namma Metro’s Phase 2 have been successfully completed, with the Bangalore Metro Rail Corporation Limited (BMRCL) announcing that the stretch will be open to the public by the end of 2026.

This underground corridor, stretching 13.75 kilometers, will connect Dairy Circle in South Bengaluru with Nagawara in the city’s northern part. The entire tunnel spans 21 kilometers, marking a significant milestone in the city’s expanding metro network.

Subrahmanya Gudge, Chief Engineer at BMRCL, highlighted that the main challenge for tunneling lay in Bengaluru’s diverse geology. Unlike cities such as Mumbai, where the basalt rock is consistent, Bengaluru’s soil composition is mixed. While soil can be easily excavated, the rock segments pose a challenge due to their hardness, leading to slower progress and the potential for over-excavation, which can cause road settlement and structural cracks in nearby buildings.

The tunnel-boring machine (TBM) encountered significant hurdles, halting 193 times between Shivajinagar and MG Road stations for repairs. In comparison, similar tunneling work in Delhi would see the machine stop only 10-12 times over the same stretch, according to Gudge.

Despite the challenges, BMRCL managed to complete tunneling work ahead of schedule, largely due to lessons learned from Phase 1. “The key to success was advanced soil investigation and the use of tunnel instrumentation,” Gudge explained. These tools helped monitor the tunnel’s behavior during construction, allowing engineers to take corrective actions swiftly and minimize any damage.

Gudge emphasized the importance of planning and preparation. “Although we didn’t have the option to investigate soil conditions every 20 meters due to surrounding buildings, we used innovative techniques to ensure stability and safety throughout the project.”

The construction of underground stations follows a bottom-up method, with the exception of Langford Town station, where a top-down approach has been implemented. A total of nine tunnel boring machines (TBMs), including six slurry TBMs and three earth pressure balancing TBMs, were deployed to complete the tunneling, which began in August 2020 and concluded in October 2024.

While the civil works for the underground corridor are nearly finished, BMRCL still has key tasks ahead. These include track laying, installation of the tunnel ventilation system, and the completion of air-conditioning, electrical, and mechanical systems. Once fully operational, this corridor will play a pivotal role in easing traffic congestion and enhancing connectivity across Bengaluru.

The Namma Metro Phase 2 underground corridor is poised to become a vital component of Bengaluru’s metro network, offering a more efficient and sustainable mode of transport for the growing city. With the completion of tunneling work ahead of schedule, the ambitious project is on track for public use by late 2026, providing a modern transit solution for residents and commuters alike.