VELIGONDA PROJECT

                              VELIGONDA PROJECT

Our long-awaited tour to pula subbayya veligonda project began on the morning of 8^th july  2011. It was an exciting start.

 Prakasam district may have to wait for three more years for completion of its dream project, Veligonda that would bring 43.58 tmcft of Krishna water from the foreshore of Srisailam project to irrigate 3.36 lakh acres in its most backward upland areas.

  Veligonda project envisages drawing flood waters of Krishna river for 45 days in a year through two tunnels running over 18.8 km in the Nallamala reserve forest and empty them into Nallamala Sagar formed by closing three gaps in the hill ranges by constructing cement concrete dams at Gottipadia, Sunkesula and Kakarla villages near Markapur. Three canals would take off from the huge reservoir to supply water in all to 4.47 lakh acres in Prakasam, Nellore and Kadapa districts. The Rs. 5,150 crore project, which should have been completed by 2008, is bogged down due to delays in drilling the tunnels, construction of dams, acquisition of land for canals and rehabilitation of 11 villages that would face submersion.  
While L & T has completed the Gottipadia dam, the other two smaller dams are expected to be completed in one year.    Meanwhile, tunnel drilling was delayed due to technical problems hampering the project. As a tiger reserve is located in Nallamala forest, manual blasting was not permitted on the plea that it would affect the big cats.

Machinery imported:
Tunnel boring machines (TBMs) were imported from Germany and US at a cost of Rs. 200 crore each. The twin tunnels would cost Rs. 1,350 crore.   Work on the first tunnel was started in May 2005 and scheduled for completion in Dec 2013. After drilling the tunnel for over 3.4 km, the machine encountered gushing water and slushy soil. It increased its speed only to get stuck in mud and stopped work for the last 11 months. All efforts to restart the machine proved futile. Experts, who came from Italy, closed the seepages spraying costly chemical. They are working strenuously to restart the machine.
The experience was rewarding for the second TBM that also drilled the tunnel up to 3.4 km and encountered same problem. But it went cautiously arresting leakages successfully. Though started one year late, it has taken over the first tunnel now and forging ahead.

Chief Minister Late Dr. Y. S. Rajasekhara Reddy said that the Rs. 4,500-crore Veligonda project would be completed in the next three years to permanently end drought in Prakasam district.

The Rs. 120-crore machine was imported from Germany to make the tunnel without disturbing wildlife in the Rajiv Gandhi Tiger Reserve. No other State had taken up construction of such a huge tunnel for irrigation purposes. Beneath India’s largest tiger sanctuary, the Nagarjuna Sagar National Park, tunnel boring machines are orchestrating one of the largest water transfer schemes in India. A Robbins Double Shield TBM is boring tunnel No. 2 of the Pula Subbaiah Veligonda project for Coastal Projects Ltd. (CPL), of the CPL/ Hindustan Construction Company (HCC) JV.

On the Krishna River, on the right bank of the Srisailam Canal, lies the future inlet site for the Pula Subbaiah Veligonda Project. Once complete in 2014, the system will draw 1.2 billion cubic meters (317.0 billion gallons) of flood water annually from the foreshore of the Srisailam reservoir.   Two parallel, 19.2 km (11.9 mi) long tunnels will transfer water via a network of five canals to over 1,600 square kilometers (395,368 acres) of farmland in the three districts of Prakasam, Nellore, and Kadapa.  Up to 243 cubic meters per second (64,193 gallons per second) of water will travel through the bored tunnels to a feeder canal.

In October 2007, a USD $180 Million contract was awarded to Coastal Projects Pvt. Ltd (CPPL). In November, CPPL signed a contract for a 10.0 m (32.8 ft) diameter Robbins Double Shield TBM and continuous conveyor system. In addition to the machine and conveyor, spares and key operating personnel were sent to the jobsite to excavate tunnel no. 2 starting from the outlet end.

The Veligonda tunnel no. 2 is located in sedimentary rock on the western margin of the Cuddapah Basin, where a number of faults and folds make for complex geology.  Rock includes quartzite with interbedded shale (60%) and shale with limestone and phyllite (40%) ranging from 90 to 225 MPa (13,000 to 33,000 psi) UCS. Two major faults are expected along with some ground water.

The Double Shield machine utilizes sixty-seven 20-inch diameter back-loading cutters to combat the tough ground conditions. Specially designed drive motors allow the machine to run at a higher than the normal RPM, compensating for low penetration rates in the hard rock.  In squeezing ground, the cutter head is also capable of vertical movement  allowing for over boring. The machine also has a probe drill which allows for verification of geology 30 m (98 ft) ahead of the TBM.  The drill is capable of 360º rotation and can alternatively serve as a grout consolidation drill.  Large 40 kW (54 hp) dewatering pumps located on the back-up system have been specially designed to pump any water away from the tunnel face. As the TBM bores, it erects 300 mm (12 inch) thick concrete segments in a 6+1 arrangement, making the final tunnel diameter 9.2 m (30 ft).

Muck haulage requires one of the most extensive conveyor systems ever used in India.  The continuous steel cable belt, the longest single flight ever provided by Robbins, will extend 19.2 km (11.9 mi) and requires four main drives and three booster drives.


Finally, having kept the cherished memories of our   tour we returned to vijayawada on 9^th july 2011 at 2AM. It was not only a pleasure trip but also an educational tour that gave us a clear idea of our theoretical subjects. We thank Almighty God for bringing us safe and sound!

................EDITOR.