Experts for soil survey on Metro UG route

Factors like karst topography (formed by soluble bedrock and debris) in certain areas, excessive groundwater extraction and construction practices have led to the cavity of roads.
Image used for representational purpose only
Image used for representational purpose onlyFile photo

BENGALURU: With a huge sinkhole surfacing on the KG Halli-Nagawara Road due to Metro tunnelling work on Thursday, experts are pitching for a soil survey, and also to check for utilities on the tunnelling route to avoid such incidents in future.

With ongoing work on Metro Reach-6 connecting Gottigere to Nagawara (22 km) and also Metro rail work in another phase, geologists observed that sinkholes pose a serious threat to these infrastructure projects.

“Factors like karst topography (formed by soluble bedrock and debris) in certain areas, excessive groundwater extraction and construction practices have led to the cavity of roads. Due to water lines and sewer lines underneath, there is a possibility of similar instances in future, as there is heavy vehicle movement. Hence, the BMRCL and BWSSB should sit together and draw up a plan. They should do a joint survey and only then proceed with tunnelling work,” said geo-environmentalist Dr D Paramesha Naik, Assistant Professor at the Department of Environmental Sciences at Bangalore University.

Renuka Prasad, former professor of geology and Coordinator of Bio Park, Bangalore University, opined that before earth work or tunnelling for the Metro or any big project, there should be a comprehensive geo-physical survey to know the water, soil, weather zone and hard rock, which could be around 30-40 km in Bengaluru, Mysuru and Southern Karnataka. Due to internal dynamics, fractures are developed in the hard rock and it is these fractures that result in sinkholes and cave in of roads. The impact of fractures in Bengaluru is very less.

“In many areas, BWSSB has changed water and sewer lines and over the period, the soil becomes loose. Due to the seeping of water either from damaged BWSSB pipes or due to rain and the movement of heavy vehicles, roads cave in, however, it may not cause any damage to Metro tunnelling work as the tunnel is 30 metres below the ground. The work may be suspended until the cavity is fixed,” said a BMRCL engineer.

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