Deep Hard Rock Tunneling in India achieves a New High
Deep below Mumbai, a Robbins 6.25 m (20.5 ft) diameter Main Beam TBM is excavating for the 8.3 km (5.2 mi) Mumbai Water Tunnel. The hard rock machine, for the joint venture contractor Unity-IVRCL, has been reaching impressive advance rates, including a recent record-breaking rate for tunneling in India. In October 2013, the TBM turned in 870.16 m (2,855 ft) in one month. The rate overturned a previous record at Kishanganga for a SELI TBM that advanced 816 m (2,677 ft) in November 2012.
The Robbins machine achieved the impressive advance rate in the size class of 6-7 m (19.7 – 23.0 ft) TBMs. Robbins Field Service Site Manager Leif Schmidt felt that good cooperation played a large part in the project success: “We have a great machine and a great client that is making every effort to do daily maintenance and cutter inspection on the TBM, with a dedicated 4-hour shift per day.”
The achievement is especially notable considering the 109 m (357 ft) depth of the launch shaft. At that depth, the sheer amount of cover, heat in the tunnel, and time to lower materials to the machine are all factors that could potentially affect advance rate. Despite these challenges, the machine has performed exceedingly well. “[The machine’s] performance is good; we would recommend Robbins machines for hard rock boring,” said Mr. Pravin Titare, General Manager for Unity.
Difficult ground conditions have also been an added challenge, including hard basalt rock, fractured ground, and water inflows. Although the machine is currently working in stable ground, tough geology was encountered in early 2013. On this topic, IVRCL General Manager Mr. Bipin Arey said, “Our team has resolved the problem, and the [Robbins] crew helped us strengthen the affected portion of the tunnel.”
The latest record isn’t the first set by the rapid Robbins TBM. In December 2012, the machine set an Indian record of 57.4 m (188.3 ft) per day. The machine has also had a best week of 252.6 m (828.7 ft). “High advance rates are expected to continue for the duration of the project,” said Mr. Kapil Bhati, Managing Director of Robbins India.
Once the tunnel is completed, it will provide Mumbai’s approximately 20.5 million residents with a consistent flow of clean drinking water, even during the seasonal monsoons that contaminate the city’s water resources.