TBM Completes third bore for Chennai metro project15 November 2017
India - On October 31 a 6.65m diameter Robbins EPBM broke through at Chennai Metro, making this the third tunnel the machine has bored for the project and for contractor Afcons Infrastructure Ltd.
After completing its original twin tunnels, the EPB was refurbished in preparation to bore its latest 1.8 km section. During refurbishment, the inner seal greasing system was changed from auto to manual mode and the foam nozzle system was modified. These changes optimized the machine for excavation in the highly variable mixed face conditions encountered in the first two tunnels.
Gopal Dey, Afcons senior manager said, “For this project, we needed a machine that was specifically tailored to project conditions from soft clay to mixed ground with rock."
The TBM was launched on February 3. According to contractor Afcons, the machine faced a major challenge right out of the gate. “When the TBM came out of the launching shaft, a few rings were erected and then the machine had to cross a live railway track, which meant there would be a possibility of ground settlement,” said an Afcons director. “At this stage, we had to closely monitor TBM face pressure and advance the machine at a uniform rate to ensure proper primary grouting.” The bore’s geology mainly consisted of clayey sand and about 60m of mixed ground.
This latest tunnel connects multiple stations along the metro line, starting from Washermenpet through to Sir Theagaraya and to Kurukpet. The Chennai Metro Project will provide much needed transportation to a rapidly developing city.