TOI on Wednesday reported on the subsidence of 8mm over three days along an 85m stretch south-west of Durga Pithuri Lane, where an 150mm subsidence since August 31 led to the collapse of several buildings. The fresh subsidence in this direction was noticed after KMRC managed to arrest soil settlement in other directions around Durga Pithuri Lane through mass grouting.
“Even though we barely have time to breathe between dealing with water seepage into the tunnel and the crumbling buildings in Bowbazar, we will start a post-tunnelling survey of buildings between the Lenin Sarani-Nirmal Chandra Street crossing and Chaitan Sen Lane, where susbsidence was noticed and some cracks have been reported,” said an engineer involved in the project.
A geo-technical analysis and a building condition survey are on the cards and attempts are on to strengthen the soil along this stretch through grouting so that the subsidence doesn’t spread.
Sources said Wednesday’s subsidence was “much less” than the past three days. On Sunday, the soil settlement was measured at 5mm, followed by 2mm on Monday and 1mm on Tuesday. “On Wednesday, it was less than 1mm. That is a good sign as it indicates that the soil is settling down,” said an official. Prior to the Bowbazar subsidence, the maximum soil settlement during and after tunnel boring was 0.8mm, well within the tolerable limits of buildings.
ITD ITD-Cementation, the contractor appointed by KMRC to construct the twin tunnels between Esplanade and Sealdah, had carried out temporary strengthening of old buildings that abound this stretch. Apart from use of scaffolding and steel props to support ceilings and archways, grouting was also carried out. Tilt meters were also installed in some buildings to detect any hint of subsidence.
The five-member committee set up to help recover and restore the Bowbazar buildings will also take a look at some of these builings. “It is quite possible that the buildings below which the TBMs have passed may be damaged because of fresh subsidence. We might be looking into these structures as well. The committee is surveying the damaged buildings of Bowbazar to identify those that can be repaired and reoccupied,” said Nitin Som, emeritus professor and former head of the civil engineering department at Jadavpur University.
According to the pre-tunnelling building condition survey, the two TBMs had to snake through 675 buildings located within 40m on either side of the tunnels. This area is also known as the TBM influence zone. These buildings were all aged beyond 60 years. Several of them are over 100-year-old. At least 400 of them were mapped as being in “very critical”.
Latest Govt Job & Exam Updates: