International and in-house experts are working on a war-footing to prevent further damage to houses in a part of Central Kolkata where tunnel boring for the East West Metro corridor led to collapse of some buildings and appearance of cracks in several others, a senior official said on Wednesday.
The Kolkata Metro Railway Corporation Ltd (KMRCL) has brought in four international experts to assist the operations to stop further ingress of water and ground settlement that caused extensive damage to the buildings at Bowbazar area.
KMRCL General Manager (administration) A K Nandy said, "Work is on in full swing at the site to prevent any further damage."
Several buildings at Durga Pituri Lane and Syakra Para Lane have partially collapsed or developed cracks owing to the incident of August 31, when an aquifer broke during tunnel boring and water and silt gushed in, leading to a severe ground loss in the vicinity.
At least 44 houses have been evacuated and residents of eight more buildings in the area may have to be moved out, the official said, adding that 381 persons have been shifted to various hotels.
Nandy and KMRCL chief engineer, civil, Deewanjee said some results have been obtained from filling the tunnel boring machines with cement slurry grouting, which is continuing.
They said, as per the advice of the experts, the frontal part of the affected tunnel is being filled up with water by creating a bulkhead to create counter-active water pressure to stop water ingress inside the tunnel.
Claiming that geotechnical investigation was done to assess the condition of the sub-soil, they said, "The sub-soil in the tunnelling horizon comprises silty sand with water bearing strata, and the possibility of encountering a high pressure-high volume aquifer cannot be ruled out."
The international experts and design consultants will review the tunnelling parameters in the affected zone to determine methodology for safe tunnelling in future.
Tunnel boring for the East West Metro corridor has been stopped and will be restarted only after the Calcutta High Court gives its nod, KMRCL lawyer told a division bench presided by Chief Justice T B N Radhakrishnan in connection with a PIL against tunnelling work in the congested areas of the city.
The East West Metro corridor would connect Salt Lake Sector V in the East and Howrah in the West.
Nandy and Dewanjee said KMRCL will reconstruct or repair the damaged buildings, adding that it "will arrange for residential flats in the interim period if the outstay for the families are for a considerable period."
Nandy said a control room has been opened by the city police and municipal corporation along with KMRCL to facilitate retrieval of personal belongings and valuables by the residents of the affected buildings, who were evacuated hurriedly.
West Bengal Chief Minister Mamata Banerjee, who visited the affected area on Monday and spoke to the residents, has urged Kolkata Metro to immediately release compensation of Rs 5 lakh to each of the affected families.
During a meeting with KMRC officials, civic and police authorities over the incident, Banerjee also urged the Metro authorities to pay monthly compensation to those whose daily income has been affected.
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 metro corridor passes through some of Kolkata's most-congested areas where there are many century- old buildings, some of which are in a dilapidated condition.
Work for 9.8 km of the 10.9-km-long underground tunnel has been completed for the East-West Metro corridor.
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