Chennai: It was to be yet another milestone for Chennai metro rail, the completion of one of the tunnels under Anna Salaibegun about six years. But after a long wait and a few tense moments on Tuesday, the boring machine literally hit a wall and was unable to break through the 3.7km long tunnel connecting AG-DMS with May Park Day station.
The cutters in the boring machine that drilled through the rocky soil wore out and could not break through the 10cm concrete wall. The giant machine had to be restarted several times before engineers decided to change the cutters. The machine had already bored through one of the toughest layers amid several such hiccups over the last 17 months.
“Tunnel building is actually complete. The machine had to just break through the concrete wall and enter the station before we conclude tunneling,” said a Chennai Metro Rail Limited (CMRL) official. “The wall the machine had to break is a metre thick. We changed the cutters on the head before it started boring but they wore out before it could breach the final 10cm. The cutters will be changed and we hope to achieve the breakthrough in a couple of days.”
Industries minister M C Sampath and principal secretary (planning, development and special initiatives) S Krishnan joined around 300 CMRL engineers and workers in safety gear to watch the operation at AG-DMS. In the afternoon, a few minutes after it began boring with a squealing noise, the machine stopped.
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For the next couple of hours, loud noises interspersed with periods of long silence filled the air.
By 4.30pm, engineers used a hydraulic breaking machine from the station side to expose the cutter head of the boring machine, but the wall was too strong. They then decided to replace the cutter head and make an attempt on or before Thursday. “We have around 450m left to build in the other tunnel. We expect to finish by next month,” an official said.