Kali Gandaki “A” Hydroelectric Power Project, Nepal
Tasks Performed: Chief Geologist/Geotechnical and Principal Design Engineer with MKI responsible for completing the detailed geologic and geotechnical investigations for this project during the project implementation phase including stability evaluation, final design, instrumentation, and construction supervision of all major excavations (desander facility, dam sites, powerhouse, surge shaft, and pressure tunnels). He supervised and directed the work of a team of native professional geologists, civil and structural engineers, surveying and drafting personnel, and a private consultant.
Duration: 1998 (7 months)
Description: The project, located on the Kali Gandaki River in Nepal approximately 180 kilometers west of Kathmandu, is a 144 MW (megawatt), run-of-river hydroelectric plant with a daily pondage capacity of 3.1 million cubic meters. The main features of the project are a 44-meter-high concrete gravity diversion dam, desander, power tunnel, and surface powerhouse. The Government of Nepal plans to have the project on line by the third quarter of the year 2000. The basis of the project is to short-circuit a loop of approximately 45 kilometers in the Kali Gandaki River by the power tunnel, about 6 kilometers in length, thus developing a gross head of about 124 meters. The main objective of the project is to meet the demand for electric power in Nepal at least cost in an environmentally sustainable and socially acceptable manner. With its installed capacity of 144 MW, the project will generate 842 GWh (gigawatt-hours) of renewable energy annually using the flow of the Kali Gandaki River.
The project includes an 18-meter-high and approximately 120-meter-long RCC cofferdam (the first RCC dam built in Nepal) which was selected to permanently protect the powerhouse against flooding. The dam required placement of approximately 26,500 cubic-meters of RCC. Placement of RCC commenced April 8, 1998 and was completed July 7, 1998 just in time to protect the powerhouse excavation from a two-year flood of the Kali Gandaki River. Unfavorable geological conditions required the dam to be placed on a foundation consisting partially of rock and partially of alluvium. Foundation settlements during the three-months construction period reached a maximum of 90 millimeters. At the time of completion, no cracks were visible in the RCC and seepage under and through the permanent RCC cofferdam was minimal (< 10 liters/second).
Final design of the surge tank back slope includes a 25-meter-high (1.0H: 3.5V) cut in overburden soils (colluvium and landslide debris) and weathered phyllite that is supported with soil dowels 12 to 18 meters in length on 2-meter-centers. The permanent soil-nailed structure (face area approximately 2,000 square-meters) is currently one of the largest in the world. The method was selected to prevent cutting into the toe of an old landslide, which would have removed much of the natural support of the slope. In implementing this method, the 28-meter-wide surge shaft was raised 13 meters, thereby eliminating the need for extensive excavation (approx.30,000 m^3) and treatment of the surge tank back slope, and reducing the risk of a large
potential slope failure.
The Kali Gandaki “A” Hydroelectric Power Project is currently the largest project under construction in Nepal and is estimated to cost approximately 470 million U.S. dollars.