PS Veligonda Project
Pula Subbaiah Veligonda Project
- Machine Type Double Shield TBM
- Diameter 10.0 m (Cross section 78.56 sqm)
- Tunnel Type: Water Transfer
- Tunnel Length: 18.8 km
- Owner: Government of Andhra Pradesh
- Location: Prakasam District, Andhra Pradesh, India
One of India's greatest water transfer systems is being carried out using tunnel boring machines beneath NagarjunaSagar National Park, the country's largest tiger sanctuary. In order to complete Tunnel No. 2 of the Pula SubbaiahVeligonda project, RPPL is deploying a Robbins Double Shield TBM.
The potential inlet site for the Pula SubbaiahVeligonda Project is located on the Krishna River, on the right bank of the Srisailam Canal. After it is finished, the system will be able to yearly remove 1.2 billion cubic meters (317.0 billion gallons) of flood water from the Srisailam reservoir's shore. Water will be delivered to more than 1,600 square kilometers (395,368 acres) of farmland in the three districts of Prakasam, Nellore, and Kadapa via two parallel tunnels that are 19.2 km (11.9 mi) long. The bored tunnels will carry water at speeds of up to 243 cubic meters per second (64,193 gallons per second) to a feeder canal.
The geology of the Cuddapah Basin, where the Veligonda Tunnel No. 2 is situated in sedimentary rock, is complicated by numerous faults and folds. Shale with interbedded limestone and phyllite makes about 40% of the rock, which has a UCS of 90 to 225 MPa (13,000 to 33,000 psi) and is composed primarily of quartzite. There are some ground waters and two main faults.
To handle the difficult ground conditions, the Double Shield machine has 67 back-loading cutters with a 20-inch diameter. Low penetration rates in the hard rock can be made up for by running the machine at a higher-than-normal RPM thanks to specially developed drive motors. The cutter head can move vertically while compressing the ground, enabling over-boring. Additionally, the machine features a probe drill that enables geology to be checked 30 metres (98 feet) in advance of the TBM. The drill can rotate 360 degrees and also be used as a grout consolidation drill. To pump any water away from the tunnel face, large 40 kW (54 hp) dewatering pumps are installed on the backup system. The TBM constructs 300 mm (12 inch) thick concrete segments in a 6+1 configuration as it drills, resulting in a 9.2 m final tunnel diameter (30 ft).
One of the largest conveyor systems ever deployed in India is needed for muck transport. Robbins will eventually offer a continuous steel cable belt that will be 18.8 km long, requiring four main drives and three booster drives.