East-West Metro’s tunnelling work resumed from Bowbazar on Tuesday (18th February 2020), more than five months after one of the tunnel-boring machines (TBMs) hit an aquifer and triggered subsidence in the congested area. Around 700 residents had to be evacuated after cracks appeared (a few of them collapsed thereafter) in several buildings.
Kolkata Metro Rail Corporation (KMRC), the implementing agency, got a breather last week when Calcutta high court allowed it to restart its tunnelling operations. Following the court order, the rest of the boring will be done strictly according to the suggestions of IIT-Madras experts. KMRC will periodically update the experts on the TBM’s progress.
The TBM will move at a very slow pace for now, rolling at 10 meters per day. KMRC MD Manas Sarkar said, “This is a new beginning for us. But you could call it a symbolic start. It might take another week for the TBM to burrow steadily. For now, the experts will closely watch how the refurbished machine behaves. They may start it and then stop it again, study the parameters and so on.”
The stretch between Bowbazar and Sealdah is the last leg of East-West Metro’s underground tunnelling. ITD-ITD Cem is the joint venture construction company building 2.5km of twin tunnels between Esplanade and Sealdah. Afcons had built the tunnels between Howrah Maidan and Esplanade. The 16km East-West Metro will stretch from Sector V to Howrah Maidan through the Hooghly riverbed. The first phase, between Sector V and Salt Lake stadium, covering 5km, had started operations last Friday.
At the inauguration, Railways minister Goyal on Thursday said the entire 16km Metro corridor will be commissioned in another two years. Now that tunnelling has resumed, even engineers involved in the project feel the target is achievable. On Tuesday morning, the resumption of tunnelling was a low-key affair. A puja was held inside the tunnel at the Esplanade site. Urvi, as the TBM boring the east-bound tunnel has been nicknamed, has remained stuck 14m under a pavement of Nirmal Chunder Street since its twin, Chundee, ran into the aquifier on August 31 last year. Urvi, stuck 400m behind, has now started digging till Sealdah to complete its own 1km of tunnelling.
On reaching Sealdah, it will take a U-turn to burrow the remaining 800m of the affected tunnel towards Bowbazar. By Wednesday, Urvi is expected to cross Nirmal Chunder Steet and reach Chaitan Sen Lane. The machine that hit the aquifer was boring the tunnel through which Howrah Maidan-bound trains will run. It had already bored 1.6km from Esplanade when the fiasco happened.
The other machine has now started digging for the tunnel through which Sector V-bound trains will ply. All these days, intense grouting has been done to strengthen the soil around the subsidence zone, which mainly comprise Durga Pituri Lane, Shyakrapara Lane and Gour De Lane, where more than 25 buildings have either collapsed or had to be razed as a precaution.
A division bench of Calcutta high court is hearing a PIL, filed by NGO Paribesh Academy, seeking the court’s intervention to ensure safety measures are taken for the rest of the tunnelling. As part of enhanced safety measures, the TBM will now be operated by staff from the machine’s German manufacturers Herrenknecht, under the supervision and monitoring of KMRC’s international consultants, General Consultants.
KMRC has formed a committee of experts for this. The committee includes Hong Kong-based geotechnical expert John Endicott, who was involved in resumption of work after the Nicoll Highway collapse, TBM expert David Christopher, Bridges and geotechnical expert N Pitchumani from Chennai. The experts had submitted a report to the court on how tunnelling would be done now. Calcutta HC wanted the expert committee report validated by institutes like IIT. The report was then reviewed by a team of IIT Madras experts led by K Rajagopal, professor and institute chair, department of civil engineering.