Multi-level car park at Freedom Park hits hard rock.

The civic body doesn't seem to have learnt any lesson from the experience of Namma Metro. The metro project suffered a massive delay when it hit hard rock while tunnelling for the underground section.

The proposed three-storey car park at Freedom Park is in the same area and has hit a rock.

Sources said that the rock is an outcrop, which essentially means that the entire multi-level car park has to be carved out of this bedrock sediment. BBMP estimates that it will have to drill through over 25,000 cubic metres of bedrock.

“While excavation is on, we have hit a hard rock after clearing around three metres of overburden earth at the site, that was essentially sediments of debris. The three-storey basement structure has a total depth of 12 metres more to go, all of which is now found to be a hard rock,” said K.T. Nagaraj, Chief Engineer (Projects), BBMP. “We cannot use dynamite like Namma Metro did. We have opted not to use even controlled explosions, as the site is right next to the erstwhile Bangalore Central Prison, which is a heritage structure. We are using diamond cutting technology to drill through the bedrock.”

However, Prof. T.G. Sitharam, Department of Civil Engineering, IISc., said that diamond cutting technology is over 10 times more expensive than normal drilling and is time consuming. “The drilling will create excessive noise and air pollution. Going by the dimension of the rock, it will take at least a couple of years to be cleared,” he said. “These rocky sediments are not contiguous. The civic body should have carried out a thorough geo-technical study, especially after Namma Metro hit a hard rock, to identify an area without bedrock.”

The Hindu spoke to some structural engineers working in other civic agencies. “Even now, the project seems to be viable, but time and cost overruns are inevitable,” one of them said.

THE HINDU