Road users passing through K.R. Circle in the city were wondering whether there was any caving in of the earth in the locality after seeing hordes of workers assembled at the spot late Wednesday.

Early Thursday, they learnt that the men were hired by a Bangalore Metro Rail Corporation contractor to execute the tunnelling work between the Central College underground station and the Vidhana Soudha underground station.

Variation of pressure

The workers were engaged in grouting, where the cavity below the ground is filled with concrete before the tunnel boring machine (TBM) passes through the alignment.

A BMRCL spokesperson told The Hindu when the TBM senses variation of pressure during tunnelling, the operators suspect cavity in the alignment.

Cavity to be filled

Before the TBM is allowed to proceed further, the cavity is filled from the surface. “The exercise had been undertaken many times before,” the spokesperson said.

“This particular cavity was sensed on the alignment of TBM 2, Margarita, even as TBM 1 Helen has proceeded beyond K.R. Circle.”

More In: Bengaluru