Vibration-mitigating track cushions, laser-based monitoring for subsidence, and grouting teams on standby — East-West Metro’s Bowbazar stretch is equipped with a range of protective measures to prevent further trouble in the once-unstable zone, officials said.
The 16.6km corridor from Howrah Maidan to Sector V has faced repeated setbacks in Bowbazar due to soil subsidence.
Passenger services on the full East-West stretch began on August 22, shortly after Prime Minister Narendra Modi launched three Metro links ceremonially.
“We have taken special measures to safeguard and monitor the Bowbazar section to ensure safe train operations,” said a senior Metro Rail official.
The 600-metre stretch had four subsidence incidents between August 31, 2019, and May 11, 2023, forcing the demolition of around 25 buildings and repairs to more than 50 others.
The area is now under technical surveillance, said officials of KMRC, the implementing agency of the East-West Metro.
Track cushions
To reduce vibrations that may disturb the fragile ground, Metro has installed Pandrol Vanguard, a specialised technology using rubber cushions on the sides and base of the tracks, in the Bowbazar tunnels.
“It reduces vibration by up to 20 per cent — ideal for sensitive urban zones,” said an official. The system was successfully tested during trial runs on the Sealdah-Esplanade stretch.
Laser monitoring
Engineers are monitoring the Bowbazar tunnels at regular intervals for even the slightest hint of soil subsidence, tilts or other anomalies using laser-guided machines.
These devices track multiple “optical targets” — fixed points marked inside the tunnel — to detect minute deviations in alignment. Engineers have fed the coordinates of the target spots into reader machines.
“The readers are placed on tripods and use laser technology to study the targets. Though they can scan over a kilometre in open space, range is shorter inside tunnels with sharp curves,” said a KMRC source.
The monitoring system categorises data into three alert levels — alert, alarm,
and action. If any reading crosses the ‘action’ threshold, immediate intervention is triggered.
“Even the slightest hint of water seepage will be detected. Grouting will be done without delay,” said the official.
Upgrade to real-time
Currently, monitoring is done manually after daily train operations end. But an upgrade is in progress.
“We are moving to a real-time automated monitoring system. Smaller versions of the current readers will be kept in the tunnels,” said the official.
These upgraded machines will automatically take readings at preset intervals — such as every two hours — and feed the data into a computer. The transition is expected to take around three months, the official said.
Expert view
John Endicott, a tunnelling expert who visited Bowbazar in 2019 after the first subsidence, outlined standard safety protocols for underground railways.
“There is a monitoring programme for all underground railways. Detailed inspections by maintenance engineers are usually scheduled during non-operational hours — typically between 1am and 4am,” he said.
“There are also types of automatic monitoring that can detect water seepage, no matter how slight, and ground movement as small as fractions of a millimetre.”
While Endicott noted he had no specific knowledge of the current work under Bowbazar, he described the standard response if signs of dampness are found.
“Checking for seepages is part of night-time inspections. If damp patches are detected, the usual remedy is to inject waterproof cement or chemicals into the surrounding soil.”
Metro Railway officials said all measures were in place.