98% tunnelling over on Pink Line, TBM Tunga breakthrough today

Bengaluru: In a significant milestone for Namma Metro, 98 per cent of tunnelling has been completed on its longest underground section, with the remaining 2 per cent expected to be finished within the next two months.

Of the 20,992 metres required for the Pink Line, 20,570 metres have been bored as of Tuesday. 

The 21.26-km line runs from Kalena Agrahara to Nagavara and has 18 stations (12 underground and six elevated). 

Tunga, the eighth Tunnel Boring Machines (TBMs) deployed for the Pink Line, is scheduled to break through at Nagavara on Wednesday. After serving Namma Metro for over three years, the German-made Herrenknecht EPB machine (S839B) will finally retire. 

This machine has undertaken four tunneling assignments for the Pink Line, starting with the Venkateshpura-Tannery Road section (822 metres) in June 2021. Its current and final task — boring a 938-metre tunnel from KG Halli to Nagavara — began on February 3 this year and will conclude on Wednesday. 

According to a senior official at Bangalore Metro Rail Corporation Limited (BMRCL), the breakthrough will be a low-key event organised by ITD Cementation India Ltd, one of the three civil contractors for the Pink Line. 

Tunga's sister TBM Bhadra is boring the parallel, 939-metre track between KG Halli and Nagavara. As of Tuesday, it has bored 517 metres (369 rings) and is expected to reach Nagavara by the end of October, the official said. This final tunneling drive, which began on April 2 this year, is also the last for the Pink Line. 

Although Bhadra has averaged 3.3 metres per day, the BMRCL is hopeful that "favourable terrain" will allow the machine tunnel at a much faster pace and reach Nagavara by October-end. To achieve this, Bhadra would have to tunnel 422 metres in less than two months, or 7 metres per day. 

"We expect good geology as we approach Nagavara and hope that Bhadra will achieve the same progress as Tunga did in July," the official told DH. 

In July, Tunga bored a record 308 metres in the same area. 

The other seven TBMs — Urja, Varada, Avni, Lavi, Vindhya, Vamika and Rudra — completed their work long ago. 

Meanwhile, the BMRCL is preparing to start laying tracks in the entire underground section of the Pink Line in the coming months. 

As of July, track-laying was 10.69% complete in the underground section between Tavarekere and Nagavara and 61.33per cent in the elevated section between Tavarekere and Kalena Agrahara. 

Track-laying between Cantonment and Nagavara is expected to start later this year, according to the official. 

Station work on the Pink Line is 80 per cent-95 per cent complete. Systems installations, including air-conditioning, signalling and traction, are also in progress. 

"We have set up rooms and are handing them over to the relevant contracts for systems installations," the official added. 

Another senior official said systems works would take another year and they aimed to open the Pink Line by December 2025.