Bengaluru: TBM Tunga embarks on final metro drive

Bengaluru: Namma Metro contractor ITD Cementation Ltd has commissioned the Tunnel Boring Machine (TBM) Tunga at KG Halli for constructing a 935-metre northbound tunnel towards Nagavara, official sources told DH on Friday. 

This will be Tunga's final tunnelling assignment and the 23rd of the 24 drives on Namma Metro's 21.26-km Pink Line, which will connect Kalena Agrahara to Nagavara via MG Road and Tannery Road. The Pink Line has a 13.76-km underground section and a 7.5-km elevated section. There are 18 stations, including 12 underground, on the Pink Line, whose deadline is March 2025. 

The German-made Herrenknecht machine (S-839) was the first TBM deployed by ITD Cementation Ltd, which is constructing 6.34-km twin tunnels and four underground metro stations (Tannery Road, Venkateshpura, KG Halli and Nagavara). 

The BMRCL deployed nine machines to construct twin tunnels totalling 20.99 km on the Pink Line. Seven of these machines (Urja, Varada, Avni, Lavi, Vindhya, Vamika and Rudra) have finished their job. Tunga, the eighth, is in its final assignment. The last TBM, Bhadra, is expected to complete its second drive and emerge at KG Halli on February 7. Afterwards, it will be launched for the Pink's Line's last tunnelling drive in late March or early April. 

If the average tunnelling speed (3.35 metres) is anything to go by, Tunga could take 280 days to reach Nagavara (935 metres). This could happen in late October. Bhadra's last drive (KG Halli-Nagavara, 939 metres) will likely finish in December. 

The earth below consists of soil, rock and a combination of both, according to officials. 

Tunga's reign

First drive (Venkateshpura-Tannery Road, 834.4m): July 23, 2021-Aug 24, 2022.

Second drive (Venkateshpura-KG Halli, 1,184.4m): Oct 31, 2022-Dec 6, 2023.

Third drive (KG Halli-Nagavara, 935m): Feb 1, 2024, onwards.