Typical operations during the shifts included ring building, pea graveling, and grouting to control any water inflows. An international crew of workers, combined with local staff in training, was assigned to the site to keep the TBM in operation for two 10-hour shifts, plus a 4-hour maintenance shift. 2 in June 2009, through mainly soft, fractured rock with little water ingress. The excavated rock from the TBM drive is then recycled for use as concrete aggregate and pea gravel.Ĭrews began excavation of Veligonda tunnel No. Once outside the tunnel in the spoil handling area, muck is transferred to spoil dumps using trucks. The long steel cable belt system is powered by a total of 4 drive systems – 1 main drive with two 300 kW motors at the tunnel portal plus 3 booster drives inside the tunnel. The setup also allows maintenance and belt splicing to be performed outside of the tunnel in an optimal environment. The Veligonda system tops out at 19.2 km, making it the longest single conveyor flight Robbins has provided. The bore path behind the TBM is nearly straight, making a powerful steel cable belt system a good option. Information can also be downloaded for viewing by the tunnel superintendent and engineers at the surface, to allow monitoring and adjustment of all TBM equipment. Real-time meters allow the measurement of parameters including cutterhead motor amperage, RPM, cutterhead power, and gripper cylinder pressure. To monitor TBM performance throughout the project, a newly designed data logging system was installed on each machine. Large 40 kW dewatering pumps located on the back-up systems have been specially designed to pump any water away from the tunnel face. The drill is capable of 360º rotation and can alternatively serve to drill grout holes for ground consolidation. Stability of the segment rings is achieved through a combination of crushed aggregate injection and grouting to fill the annulus outside the lining.Ī probe drill mounted on the machine allows for verification of geology 30 m ahead of the TBM. In squeezing ground, the cutterhead is also capable of vertical movement to allow for overboring.Ĭontinuous lining behind the machine consists of 300 mm thick concrete segments in a 6+1 arrangement, making the finished tunnel diameter 9.2 m. Specially designed drive motors also allow the machine to run at a higher than normal RPM, compensating for low penetration rates in sections of extremely hard rock. The 10.0 m Double Shield TBM is mounted with back-loading 20-inch diameter cutters for more efficient excavation, particularly in the high rock strengths present. The quartzite sections with interbedded shales can also be very blocky in nature – the layering of hard quartzite with thin, weak shale makes over-break in the crown and shoulder of the tunnels a possibility. In general, the high quartz content of the rock in the Veligonda tunnels tends to cause high abrasive wear during tunnelling, making larger diameter, 20-inch disc cutters the best option for longer cutter life. Two major faults are expected along with some ground water. Rock includes quartzite with interbedded shale (60 %) and shale with limestone and phyllite (40 %). The Veligonda tunnel path is located in sedimentary rock on the western margin of the Cuddapah Basin, where a number of faults and folds make for complex geology. 1 is currently under excavation by the NSC Consortium – a JV of local firms Nuziveedu Seeds, Swathi Constructions and Coastal Projects – using a 7.9 m diameter Herrenknecht Double Shield. A Robbins Double Shield TBM and continuous conveyor system, as well as spares and key operating personnel, were supplied to the jobsite to excavate tunnel no. The 180 million USD contract was awarded to the Coastal Projects Ltd (CPL)/Hindustan Construction Company (HCC) JV. Up to 243 m 3/s of water will travel through the bored tunnels to a feeder canal. Two parallel, 19.2 km long tunnels will transfer water via a network of 5 canals to over 1,600 km 2 of farmland in the 3 districts of Prakasam, Nellore and Kadapa. Once complete in 2014, the Veligonda system will draw 1.2 billion m 3 of flood water annually from the foreshore of the Srisailam reservoir. The Andhra Pradesh Irrigation Department hopes to alleviate the chronic drought conditions and contaminated drinking water in the region with a massive water transfer scheme consisting of over 120 km of tunnels, all sourced at the Srisailam Dam on the River Krishna.Īt the right bank of the Srisailam Canal lies the future inlet site for the Pula Subbaiah Veligonda Project, one section of the overall water transfer scheme. Eastern areas of India’s Andhra Pradesh state receive only 20 cm of rainfall per year - an amount comparable to Africa’s Kalahari Desert.
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