TBM Tunga achieves Final Breakthrough for Bangalore Metro Phase 2 at Nagawara Station

Bengaluru, India (Metro Rail Today): ITD Cementation India has celebrated a significant milestone with its tunnel boring machine (TBM) S-839B, nicknamed Tunga, achieving its final breakthrough at the South Shaft of Nagawara Station on the 21.386 km Bangalore Metro Pink Line (Reach 6) project.

Tunga’s breakthrough marks the completion of its fourth and final assigned tunneling drive out of a total of four planned for the 73.92 km Bangalore Metro Phase 2 project’s 4.591 km Package RT-04, which stretches from Tannery Road to the North Ramp.

Commissioned in June 2021, the Herrenknecht mixed-shield Earth Pressure Balance (EPB) machine Tunga successfully bored a 938-meter tunnel from Kadugondanahalli Station’s north shaft to a cut-and-cover shaft south of Nagawara Station, crossing the Outer Ring Road (ORR).

Tunga commenced its final drive on February 1, 2024, navigating through challenging mixed-face hard rock conditions typical of Bengaluru’s geology. By the end of June, it had completed 469 meters, despite encountering two significant sinkholes. Overcoming these obstacles, Tunga achieved a notable performance in July, boring 308 meters and setting a local monthly record due to favorable soil conditions.

A summary of Tunga’s tunneling drives includes:

• Venkateshpura to Tannery Road (822 meters): June 2021 – June 2022
• Tannery Road to Shadi Mahal TBM Retrieval Shaft (209 meters): June 2022 – August 2022
• Venkateshpura to Kadugondanahalli (1184 meters): October 2022 – December 2023
• Kadugondanahalli to Nagawara South Shaft (938 meters): February 2024 – September 2024

With Tunga's mission complete, it becomes the eighth of nine TBMs to finish its tunneling assignments for Bangalore Metro Phase 2. The only remaining TBM, Bhadra (S-840B), is working on the parallel down-line tunnel and has approximately 409 meters left to tunnel. ITD Cementation is targeting an October 26 breakthrough for Bhadra, contingent on progress and availability of state ministers for the final event.

The scope for Package RT-04 involves constructing a total of 6.34 kilometers of twin tunnels, a 360-meter ramp at Nagawara, and four underground stations at Tannery Road, Venkateshpura, Kadugondanahalli (formerly Arabic College), and Nagawara.

As of now, tunneling for the entire up-line tunnel is complete, with overall tunneling progress for Bangalore Metro Phase 2 at 20,582 meters out of 20,992 meters. To date, 25 of 26 tunnel breakthroughs have been achieved, with the breakdown as follows:

• Package RT-01: 8/8 breakthroughs by Afcons
• Package RT-02: 4/4 breakthroughs by L&T
• Package RT-03: 6/6 breakthroughs by L&T
• Package RT-04: 7/8 breakthroughs by ITD Cementation

The final breakthrough is eagerly awaited, marking another significant step in the Bangalore Metro Phase 2 project.