Since June 2018, the twin Robbins Crossover TBMs have been excavating two 2.8 km long tunnels for the new metro line 3 in Mumbai in parallel. The twin 6.65 m diameter machines were built for the application in mixed geology. They combine features of a hard rock Single Shield TBM and an Earth Pressure Balance machine and are not only able to bore in hard rock, but also operate in soft ground, using a screw conveyor at each machine’s centreline with a bulkhead gate and discharge gate. The mixed grounds in Mumbai consist of basalt, shale, tuff and breccia. Water pressure can reach up to 2 bar during the excavation works. Such mixed geology pose particular challenges to both machines and material. This, in turn, places high demands also on the components in the tunnel boring machines.
Main Bearings Designed for High Continuous Loads
Liebherr main bearings are specially designed for high continuous loads and reliable, fail-safe drilling. “Liebherr is a partner we can depend on to supply the most critical components on our machine”, says Mike Kolenich, Director of Supply Chain at Robbins.
The three-row roller bearing with a diameter of 2640 mm (114 in) ensure an even rotation and a stable load transmission on the cutter shields to achieve highest bore quality. Also the ring gear was supplied by Liebherr for the project, measuring the diameter of 1924 mm.
“In general, Liebherr has provided an excellent product within the schedule restrictions given by the customer. We visited Liebherr facilities in Germany and remained impressed with the overall organization of the production line, the clean and efficient working environment,” explains Matias Iovine, Project Manager Mumbai Metro at Robbins.
The most recent breakthroughs for the two Crossover machines were on October 3 and October 22, 2019, when they completed 499 m of tunnelling between Vidhan Bhavan and Churchgate stations. Starting from January 25 and February 15, 2020, correspondently, the machines are now boring their third drive and are expected to break through in May 2020 on a 700 m drive. The project is expected to be finished in December 2021.