TBM advances on deep Mumbai water tunnel

11 July 2012

Partial onsite first time assembly (OFTA) of the TBM allowed it to begin boring soon after shop commissioning.

A Robbins 6.25 m diameter Main Beam tunnel boring machine (TBM) from Robbins has made good progress on the start of an 8.3 km water tunnel in Mumbai, India. Following its launch in June, the contracting joint venture, Unity-IVRCL has used the machine to drive the first 320 m through the basalt rock.

The tunnel is designed to alleviate Mumbai's leakage problems in Mumbai's aging water infrastructure and provide the city's inhabitants with a consistent flow of clean drinking water. Due to the urban location of the tunnel, the TBM was launched from a 109 m deep shaft, and its launching sequence included an initial start-up excavation of 50 m with vital back-up decks connected to the TBM using cables.

This initial bore began March 30, 2012 and upon completion, the decks were lowered and a continuous conveyor system was installed for muck haulage and storage. Although the lack of conveyors during the initial bore was challenging, current advance rates are averaging 3.5 m (11.5 ft) per hour.

V.D. Sharma, director of operations at Unity Infrastructure said, "Robbins has made an outstanding effort during the excavation, without many difficulties, which speaks to their knowledge and team spirit."

Robbins assembled the TBM for the first time on site, rather than pre-assembling it at its Asian manufacturing hub in Shanghai, China. Robbins said this Onsite First Time Assembly (OFTA) initiative saved the contractor both time and money.

Difficult ground conditions are expected during excavation, including hard basalt rock, fractured ground and possible water inflows. In preparation, the TBM has been equipped with 482 mm 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. The tunnel will provide the city's approximately 20.5 million residents with a reliable water supply, even during the seasonal monsoons that regularly contaminate Mumbai's water resources.