Bengaluru: Final two TBMs on Pink Line hit rough terrain

The 21.26-km line unlikely to open by March next year, as announced by BMRCL
TBM Bhadra is yet to complete a 770-metre stretch to reach the finishing line at Nagawara South
TBM Bhadra is yet to complete a 770-metre stretch to reach the finishing line at Nagawara South

BENGALURU: The final two Tunnel Boring Machines (TBMs) completing tunnelling for Bengaluru Metro's undergound stretch of the Pink Line, from Kalena Agrahara to Nagawara, have run into rocky terrain. This has forced them to tunnel at just half the usual speed, which makes it impossible to meet the tunnelling deadline of August-September 2024, and a year-end completion appears a possibility now. The 21.26-km line is unlikely to open by the March 2025 deadline announced earlier by Bangalore Metro Rail Corporation Limited (BMRCL).

Seven of nine TBMs have completed their jobs, but the last stretch between KG Halli and Nagawara South is still pending. Tunga and Bhadra are still tunnelling on the third and final leg of their journey. When they complete their job, tunnelling on the longest underground corridor of Bengaluru Metro will end. ITD Cementation India is the contractor here.

A Metro source told TNIE, "We have completed 19.66km of 20.99km of tunnelling work for the twin tunnels (Up and Down) which translates to 93.6 per cent of work done. However, both Tunga and Bhadra, drilling parallel, have now encountered rocks. As per the geological report we have, this segment is supposed to have soil but rocks have been found now."

TBMs need to tunnel 940 metres each from KG Halli towards Nagawara. "As of now, Tunga which had an early start (Feb 3) needs to complete 550 metres to reach the finish line, while Bhadra which began on April 2, needs to tunnel 770 metres more."

If the tunnelling surface has soil, the TBMs cover at least 5km per day. "At present, they are covering only 3km per day as it is extremely difficult to bore through rocks and they drill quite slowly," he explained. The machines easily suffer wear and tear when boring hard surfaces, and the parts need to be replaced at regular intervals. The TBMs had begun their first drive from Venkateshpura to Shaadi Mahal shaft (between Pottery Road and Tannery Road). They were lifted and transported by road back to Venkateshpura, from where their second drive began to KG Halli.

On a possible deadline, another source said, "If the rocky surface gives way to soil after some time, then completion by December 2024 is possible. If the rocky terrain continues, we will need a few more months to complete tunnelling." The Pink Line has 18 stations, of which 12 stations are underground, covering 13.76km and the remaining stations are elevated and cover 7.5km. Asked if tunnelling delay would be responsible for holding up the entire line, the source added, "There is work yet to be done at the stations and much more before the line can be considered completed. Tunnelling cannot be singled out as the reason for it."

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