Around 60 per cent of pile caps have had to be redesigned during the construction of the Metro 7 due to the presence of underground utilities, officials said. For the Metro 2A, the figure is 35 per cent. Pile caps are underground concrete slabs used to give a structure a stable foundation.
While around 200 piles have been completed for Metro 7, for Metro 2A, 162 piles have been completed. Utilities, like water supply pipelines, sewage pipelines, storm water drains, gas pipelines and telephone lines are laid underground and the metro authorities have to work around them to prevent damage to them. “We have to be very cautious. We do an initial trenching of up to 3m to identify utilities. But at some points, the utilities are deeper than that. There, we even use ultrasonic machines to detect them. Once identified, we design our pile caps in a way that the utilities are not affected,” said an engineer working with the Metro 7.
Four piles are required to be made for viaducts and eight for station areas and they go up to the depth of 9-17 metres. The engineer said the utilities are all along the alignment but need to be worked around only when the construction is at the side of the road. “Of the 16 km, 13 km are at the side and only 3 km are at central median,” he said.
While sewer lines can be identified more accurately due to the presence of man holes, water pipelines are a challenge. “We seek layout maps from the civic body and sometimes call their staff to identify them,” said an official working on the Metro 2A. However, for Metro 3, they have no option but to shift or support the utility lines, officials said. “We have to deal with utilities at all places where we have to create open pits like station areas and launching shaft. Where we cannot divert them we just support them until we complete work,” said SK Gupta, Director (Projects), MMRC.
Despite precautions, there have been some untoward incidents, such as a gas leak at Cuffe Parade in January, another one at Western Express Highway in March and recently, the entry of sewer water in water supply pipelines of Churchgate. “Because of our precautions, we have been able to limit the number of such incidents,” said Gupta.