Metro-3: Tunnels for Colaba-Bandra-Seepz line will shake foundations of 100-year-old buildings
Tunnelling is expected to start in October after the monsoon and these building will come under threat of developing cracks or worse from the vibrations caused by giant machinesmumbai Updated: Aug 23, 2017 10:12 IST
Several old and dilapidated buildings, some a 100 or more years old, in the Girgaum-Kalbadevi belt could be shaken to their foundations or worse by tunnelling for the 33.5-km underground Colaba-Bandra-SEEPZ Metro-3 line. What is more, the Mumbai Metro Rail Corporation (MMRC) says it cannot be blamed for any damage and that the contractor will be held responsible.
Tunnelling is expected to start in October after the monsoon and these building will come under threat of developing cracks or worse from the vibrations caused by giant machines boring 20-25 metres down into the bedrock. The congested Girgaum-Kalbadevi area has a large number of residential and commercial buildings built a century ago.
Hindustan Times has accessed the reports of a recent survey conducted to assess structural health that found at least five buildings in Kalbadevi, Chira Bazaar and Girgaum, were vulnerable and in an “unsatisfactory” condition.
The survey says the structural strength of five buildings — Kareem Manzil, HB Wadia, Kerawalla, Singapuri, and Sukhadwala -- was “generally unsatisfactory”. It means these buildings are susceptible to damage once tunnelling starts. More buildings could fall in this category as the survey is still going on. The reports are being prepared separately for each building.
The occupants are a worried lot. “If you go by that statement that the structural health of the building is unsatisfactory, then 90% of the buildings in the area would fall under that,” said Jamshed Sukhadwalla, who has an office in Singapuri building on JSS Road, Kalbadevi. The survey reports also stated that that cracks in the building range from minor to severe and residents fear the vibrations during tunnelling could worsen the condition and lead to a collapse.
Ashwini Bhide, managing director of MMRC, however, insisted that the vibrations caused by the metro construction work won’t be as risky as was being portrayed. “Vibration, at times, is a perception issue rather than a safety one. Often when a bus or truck passes there is vibration. If required, the contractors have to shift the residents of a building at their expense for a period of seven to eight days till the tunnelling is done. If the building collapses, it is the responsibility of the contractor,” Bhide said.
On Tuesday, the MMRC initiated the process to demolish and rebuild 19 buildings in Girgaum–Kalbadevi that come in way of the Metro project. The residents had been notified earlier and will be provided alternative accommodation until their homes are rebuilt.
In 2014, the MMRC had conducted a preliminary survey to access the structural health of 1,435 buildings in the Metro-3 zone. The survey said the structural weakness of 668 buildings was “very severe” to “moderate”. This included the five in the section between the proposed CST Metro station and the proposed Grant Road Metro station. Tunnelling can set off strong vibrations for 50 meters on either side of the tunnel and this is called the ‘influence zone’ in technical parlance. Along the Metro 3 route there are 16 vulnerable buildings whose structural weakness has been categorised as very severe.
Bhide said a preliminary survey of the ‘influence zone’ has been prepared. “The data has been given to the contractors. Since the construction risk is with the contractors, they also have to do due diligence. After they carry out a detailed pre-construction study we will know the exact number of the vulnerable buildings. Then it is the responsibility of the contractors,” she said.
“The tunnelling will happen 20m to 25m below the ground; most of the shocks would be absorbed by the hard rock. There are scientific methods to monitor the health of structures,” Bhide said.
First Published: Aug 23, 2017 10:09 IST