Uneven soil in Bengaluru slows down Metro TBM work

BENGALURU: Bangalore Metro Rail Corporation Limited’s (BMRCL) Tunnel Boring Machine (TBM) ‘Bhadra’ is facing a peculiar problem, and it is considerably slowing down its pace of work.

The varied nature of soil that caused two sinkholes in its 1,200-metre tunnelling stretch between Venkateshpura and Shaadi Mahal, and concerns about the safety of a statue of Dr B R Ambedkar that could have got damaged because of vibrations or possible cave-ins, have slowed down TBM Bhadra’s progress in the phase-2 Namma Metro works.

Last month, TBM Bhadra’s operations led to a second sinkhole on Tannery Road. Not many knew about it as it was within a barricaded portion on Tannery Road. This is the second time Bhadra is facing a sinkhole issue.

TBM work: Statue safety, sinkhole worry BMRCL

It started its underground tunnelling on June 17, 2021 on the Venkateshpura-Shaadi Mahal stretch. Three months later, the ground caved in near Venkateshpura Metro station, just 110m from the starting point.
A senior BMRCL official said, “The soil here is varied in nature. It is loose on top and hard below. A sinkhole cropped up last month measuring 3m in diameter. Totally, 45 cubic metres of concrete was poured from above to fill it up before the machine could proceed.”

The other matter topmost on the BMRCL’s mind is extreme caution not to disturb an overground statue of Dr BR Ambedkar. The TBM Bhadra tunnelling works last week happened just 50 m below a statue of Dr B R Ambedkar on Tannery Road. “We had to create concrete grouting below it to ensure it did not get impacted in any way,” the official added.

BMRCL MD Anjum Parwez confirmed to TNIE that TBM Bhadra was tunnelling at a very slow pace due to problems posed by the uneven nature of the soil enroute. Because of the varied nature of the soil on the stretch, last month, TBM Bhadra tunnelled just five rings (7 m), while in November it has bored 20 rings (28 m) till date. “The TBM can average 10 rings or 14m in a single day in normal ground conditions,” explained a BMRCL official.

The TBM has also suffered much wear and tear due to the terrain. “We had to do three stoppage for repairs as a total of 40 cutter discs on the Cutter Head were damaged while tunnelling,” he said.