The source of the sinkhole that popped on Brigade Road on Thursday remains unclear. Both the BMRCL and the BWSSB say they are not at fault.
The mystery will remain unsolved for some time as metro authorities say a thorough investigation may not be possible.
A senior BMRCL official said the only way to find out the source of water leakage that loosened the soil and created the sinkhole was to dig a trench by closing the road. “It’s simply not possible,” he told DH.
Checking the alignment of water pipelines and power cables that run underground is not possible either. “The (underground) cable detector method is not very accurate,” he explained.
Soil testing through soil penetration indicates seven metres of soil below the road surface. Of this, up to 5 metres is slightly loose soil. The next layer is three metres of hard soil, below which sits the tunnel crown. The diameter of the tunnel area is 6.7 metres. The tunnel crown is 10.5 metres below the road surface.
“There is absolutely no problem in the tunneling area,” the official said.
One possible source of water leakage could be a private sanitary connection that’s not connected to the sewer, he added.
Tunnel Boring Machine (TBM) Lavi is about 40 metres from the location of the sinkhole and is expected to emerge at its destination (Rashtriya Military School) in early February.
An official from the Bangalore Water Supply and Sewerage Board said although an old water pipeline passes from Vellara Junction to Halasuru, it bypasses the location of the sinkhole by at least 100 metres. “There’s been no damage to the pipeline,” he said.
Late on Saturday night, metro authorities again closed the stretch of the road where the sinkhole had appeared. Workers dug several holes as part of soil testing to look for possible cavities under the road.