Robbins HP TBMs bore water tunnels in Andhra PradeshOn 24.06.2009 a 10.0 m High Performance (HP) Robbins Double Shield started to bore under the Nagarjuna Sagar National Park, the second tunnel of the Pula Subbaiah Veligonda project, one of the largest water transfer schemes in India, for Coastal Projects Pvt. Ltd, a sub-contractor to the SEW/Hindustan Construction Company (HCC) JV. The reservoir intake will be located approximately 60 m away from the first 7 m diameter tunnel, which is currently being excavated. For more on the project click in/42.Using Onsite First Time Assembly (OFTA), the Double Shield was assembled in approximately four months and completed in late May, 2009. OFTA is a process that allows machine components to be initially assembled at the jobsite, rather than in a manufacturing facility, typically providing savings in terms of man-hours and shipping costs.Assembly went well despite harsh local temperatures, which can climb to 45°C daily. In addition, some components could only be installed at night due to thermal expansion in the midday heat. Robbins is now providing a formal training programme for contractor personnel, covering all aspects of TBM maintenance and operation prior to the launch.Utilizing backloading 20 in cutters, the Veligonda machine will excavate a mixture of quartzite, shale, and phyllite from 90 to 225 MPa UCS. As the TBM bores, it will erect 300 mm thick concrete segments in a 6+1 arrangement, making the final tunnel diameter 9.2 m. Muck haulage will require one of the most extensive conveyor systems ever used in India. The continuous steel cable belt, provided by Robbins, will extend 19.2 km and will require four main drives and three booster drives. All tunnels are scheduled for opening in 2014. The TBM HP Robbins Double Shield ready to bore the second tunnel At the nearby Alimineti Madhava Reddy (AMR) tunnel, an identical 10.0 m HP Robbins Double Shield has been built in June, using OFTA. The machine will join another Double Shield of the same diameter that has been boring at the opposite end of the tunnel since May, 2008. For more on the AMR project click here and in/45. Both AMR and Veligonda projects draw water from Srisailam Reservoir and are part of the Andhra Pradesh government's massive scheme to provide ample irrigation and drinking water in the drought-prone region. Visit www.robbinstbm.com 27/09