Foam from metro work spurts on to suburban rail track in Chennai

Foam from metro work spurts on to suburban rail track in Chennai

Chennai (MAS): Slurry and foam from a metro rail tunnel made way to the railway track near Fort suburban railway station on Wednesday, raising concern and confusion among commuters and railway staff.

Slurry oozed out and submerged one of the two tracks at the station after a suspected opening or loose soil led to leak of pressure generated by the tunneling machine at work 15m below. Metro rail is building a tunnel from the high court to Central, and a portion of the underground alignment passes underneath Fort railway station as it turns from NSC Bose Road to Poonamallee High Road.

The machine was boring underneath the railway track when the accident happened around 6.15pm. Tunnel boring was stopped and metro engineers rushed to the railway station and assessed the damage. The slurry was removed immediately before it could cause disruption of trains. “The machine injects foam to soften the earth before boring. It is a harmless chemical,” said a metro rail official.

“It was assessed that land on which the platforms and tracks are located is strong enough and allowed trains to pass by after the sludge was removed,” said a senior official of metro rail. Changes on the surface like displacement and settling of soil are studied using sensors when a machine is boring underneath. “We would have told the railways to stop train services if the leak had an impact on the surface. Steps will be taken to prevent a repeat. We have to bore under the tracks because the alignment comes under the railway like an arc to turn into Poonamallee High Road from high court,” he added.

Metro rail uses earth pressure balance tunnel boring machines which use pressure to hold up a few feet of earth in front of its face before it bores and moves forward. Bore wells and weak soil pose a problem when the machine is used. Bore wells dug by residents were sealed along the alignment to prevent such accidents.

Slurry and foam have burst out from underneath into streets, homes and shops because residents did not inform officials about the presence of bore wells. “An abandoned bore well can create a problem for us because the pressure can come up through the tube,” said an official.

Slurry and thick foam leaked into Arunachala street at Chintadripet in June 2013. A hole developed in the middle of the road and spewed out foam due to the pressure generated by a tunnel boring machine beneath the ground. A metro rail tunnel boring machine was then digging underground from May Day Park, opposite Chintadripet railway station, to the new secretariat.