Afcons uses Robbins EPB TBM to Complete Third Bore for Chennai Metro Project
Contractor Afcons Infrastructure Ltd used a 6.65 m (21.8 ft) diameter Robbins EPB TBM to bore through in Chennai Metro, making it the contractor's third tunnel to be bored by the machine for the project. The three separate bores for the EPB are part of an increasing trend as many Robbins EPBs have been used on multiple tunnel drives with good performance.
Robbins EPBs are built one third heavier than any other EPB in the market and are designed for 10,000 hours of usable life, making them ideal for use over many kilometers. “Robbins is known for designing resilient machines,” says Mr. Gopal Dey, Afcons Senior Manager. “For this project, we needed a machine that was specifically tailored to project conditions from soft clay to mixed ground with rock. Robbins EPB TBMs have unique design features that optimize the machine for the geology.”
After completing its original twin tunnels, the EPB was refurbished in preparation to bore its latest 1.8 km (1.1 mi) 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.
The EPB was launched on February 3, earlier this year. 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,” says Afcons Director, Mr. Manivannan. “At this stage, we had to closely monitor TBM’s face pressure and advance the machine at a uniform rate to ensure proper primary grouting.” The bore’s geology mainly consisted clayey sand and about 60 meters (197 ft) of mixed ground.
Adds Mr. Dey, “We chose this machine for this project due to the underground geology in Chennai, which continuously changes from soil to mixed ground. We also liked that
On Tuesday, October 31, 2017 a 6.65 m (21.8 ft) Robbins EPB made its third breakthrough at India’s Chennai Metro.
Robbins and contractor Afcons celebrate the breakthrough and good performance of the EPB, which achieved rates up to 80 mm (3 in) per minute in mixed ground conditions.