A committee of experts on Friday submitted a report to the Calcutta High Court certifying that a tunnel boring machine (TBM) can be shifted at Bowbazar, where an aquifer burst during tunnelling led to the collapse of several houses in August.
The committee, comprising experts from various countries, said in its report that shifting of the TBM by up to five metres for maintenance of the machine was required and would be done under its supervision.
On November 8, hearing a PIL seeking termination of underground drilling for metro tunnels in congested areas, the high court had asked the Kolkata Metro Rail Corporation (KMRC) to submit expert opinions by November 15 on the feasibility of moving a tunnel-boring machine at Bowbazar.
"The committee members are of the unanimous opinion that the shifting of the TBM by about five metres will not result in soil subsidence and will as such not affect life or property above the ground over the distance over which the machine is proposed to be shifted," said the report submitted by the KMRC.
The KMRC which is executing the East West Metro project in the city had told the high court on November 8 that the TBM has been at the site since the August 31 accident and is required to be moved by five metres to ensure it remains functional.
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To ensure protection against any such eventuality, the committee proposed that the ground around the TBM be sealed with polyurethane grout and the work be carried out under the supervision of the committee which will be represented on the site by its chairman throughout the operation.
The report said additional monitoring points will be installed on the surface and below at the location to detect any ground movement at depth.
The expert committee is headed by Dr Leonard John Endicott, a geotechnical expert from Hong Kong.
The other members are Guy David Christopher Bridges, tunnel boring machine expert from Hong Kong., Neelakantan Kumar Pitchumani, a geotechnical expert from Chennai and Suman Dutta, a structural expert from Kolkata.
The petitioner's lawyer submitted before the division bench of Chief Justice T B N Radhakrishnan and Justice Arijit Banerjee that they need to have the report examined by their own experts, which the court allowed.
The bench fixed the matter for the next hearing on November 18.
The KMRC sought the permission of the high court since it had earlier directed the Corporation not to commence any work in the tunnel at Bowbazar without its nod.
The PIL has also challenged the provisions of Metro Railway (Construction of Works) Act, 1978.
Two TBMs were deployed to dug two parallel tunnels for the underground East West Metro line, when the accident in Bowbazar happened involving one of these. Several buildings in the congested area collapsed or developed cracks, leaving hundreds homeless.
The KMRC has told the court that work for 9.8 km of the 10.9-km-long underground tunnel has been completed for metro corridor.
Tunnels have been bored under the Hooghly river to connect the twin cities of Kolkata and Howrah through the rapid transit system, spanning a length of 16.6 km from Howrah Maidan to IT hub Sector V in Salt Lake.
The new corridor passes through some of Kolkata's most-congested areas dotted by many century-old buildings, several of which are in a dilapidated condition.
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