Cave-in on Nandidurga Road

This is the fourth such case in last two weeks

The sight that awaited motorists on Friday morning on Nandidurga Road.

Apart from potholes and worn out stretches, motorists now have to grapple with roads suddenly caving in. In just two weeks, four instances of portions of roads caving in have been reported.

Motorists commuting on Nandidurga Road on Friday morning were in for a surprise. A BBMP garbage compactor was stuck in the middle of the carriageway in a portion of the road that had caved in.

The cause

T.G. Sitharam, Department of Civil Engineering, Indian Institute of Science, said that one of the prime reasons is seepage of water and movement of loose soil particles according to the gradient of the road. He said that most times the road dug up is not filled up and properly compacted, leading to loose earth. “Most times, asphalting is done a few days after the ground is filled up with mud, leading to seepage of water apart from leakage from BWSSB lines, which may later cause sinkholes,” he said.

He added that sinkholes need not open up in the same places where the road was dug up. The soil below will move if there is a natural gradient. This may also cause a sinkhole or cavity in the place from where the soil has moved.

Prof. Sitharam also added that in most cases, civic agencies only re-lay the surface layer and not strengthen the sub-base layer. Road layer specifications depend on the load that the road takes. But this is rarely followed, he pointed out.

K.T. Nagaraj, BBMP’s Superintending Engineer, disagreed and said that the cavities are created when the volume of mud/soil reduces, which could be caused due to water seepage. “Such cavities are usually formed in waterlogged areas and not because the sub-base is not strengthened. The cavities are formed around six feet deep, which causes the road to cave in,” he explained.

Guidelines for road repair

The Bangalore Water Supply and Sewerage Board (BWSSB) will soon issue guidelines on restoration of roads after water and sanitary pipelines are repaired. BWSSB Chairperson T.M. Vijay Bhaskar said that currently, mud from the same spot is filled in after the repairs. “There may be some loss in mud. Road repairs can be taken up only after proper soil consolidation. Under the new guidelines, we have suggested use of quarry dust. This will add to the strengthening process and ensure that the road does not cave in,” he said. The guidelines are expected to be issued some time next week.