Deep level drive for Robbins TBM in Mumbai Jul 2012
Desiree Willis, Technical Writer, The Robbins Company
- Deep beneath the streets of Mumbai, and after its partial Onsite First Time Assembly (OFTA), a 6.25m diameter Robbins gripper TBM is into its 8.3km water supply tunnel drive to alleviate leakage problems from the city's aging supply lines and provide inhabitants with a consistent flow of clean drinking water. Launched at the bottom of a 109m deep shaft in June by construction JV Unity-IVRCL, the machine had completed 320m through basalt rock to July 4.
- A sequenced launch at the bottom of the deep shaft, included an initial start-up excavation of 50m with vital back-up decks connected to the TBM using cables. With the start-up drive completed, the decks were lowered and a continuous conveyor system was installed for muck haulage.
- The Robbins OFTA concept was used to assemble the main bearing, lube system, back-up decks and horizontal, vertical and stacker conveyors. Assembling the parts at the jobsite saved the contractor both time and money by eliminating pre-assembly at the manufacturing facility in Shanghai, China. Assembly took place at the shaft bottom in a 100m long starter chamber and a 50m long tail tunnel. TBM components were lowered into the shaft using mobile and gantry cranes.
TBM acceptance by Unity-IVRCL managers in Shanghai, China
- Following the initial excavation, V.D. Sharma, Director of Operations at Unity Infrastructure said: "Robbins has made an outstanding effort during the excavation, without many difficulties, which speaks volumes about their knowledge and team spirit." Although the lack of conveyors during the initial bore was challenging, current advance rates are averaging 3.5m/hour.
- Difficult ground conditions are expected during excavation, including hard basalt rock, fractured ground and possible water inflows. In preparation, the TBM is equipped with 482mm (19in) cutters and a probe drill. Rock support has been applied during the initial stretch of tunnel.
- Once completed, the Mumbai Water Supply Tunnel will run between the Kapurbawdi and Bhandup areas to provide a reliable water supply to approximately 20.5 million residents of Mumbai, even during seasonal monsoon rains that regularly contaminate the city's water resources.
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