Nathpa Jhakri hydroelectric project

Name of Project:

Nathpa Jhakri hydroelectric project



Country:
India

Client:
Nathpa Jhakri Power Corporation Ltd. (NJPC)

Construction period:
July 1993 – July 2002

The Nathpa Jhakri project, located in the mountainous area of the state of Himachal Pradesh, about 160 km from the city of Shimla, uses the waters of the upper reaches of the Satluj River for hydroelectric purposes.
The facility includes a 67.50-m-high concrete gravity dam which diverts 400 m³/s of water through four underground sand traps discharging into a headrace tunnel (HRT) that is 27.3 km long, at the end of which a surge tank will be built.
In addition to the surge tank, the tunnel will be linked to three penstocks feeding into six 250-MW generator units located underground in the power plant, which will exploit a drop of about 292 m.

Contract No. 2.2
This contract includes construction of the headrace tunnel from the 16,042 m point to the 27,374 m point, and the surge tank.
The tunnel passes through the Himalayan range with a coverage of more than 1,400 m.
The main characteristics of the works covered by the contract are described below.

Headrace tunnel (HRT)
Conventional excavation and concrete lining of a tunnel section 11,253 m long with an excavation diameter ranging from a minimum of 11.35 m to a maximum of 12.35 m, with an inside diameter ranging from 10.15 m in the concrete-lined section to 8.50 m in two reinforced stretches totaling a length of 1,086 m, at the Manglad and Daj streams.
Water inflows of up to 300 l/s were encountered while excavating the tunnel, at a temperature of 45-50 degrees Celsius.
Building of four access windows for a total length of 1,944 m, with a diameter of 7.50 m.
Consolidation drilling and grouting, anchor bolts for rock, test boring, and control instrumentation.
Design, supply, and installation of a Howell Bunger 1,000-mm-diameter valve equipped with all its accessories, placement of a pipeline in the Manglad window for possible drainage of the HRT, and construction of a channel to discharge the water into the stream.

Surge tank
Excavation of the 296-m-deep concrete-lined surge tank with an excavation diameter of 24.50 m for the first 225 m, and 10 m for the remaining 71 m.
Construction of a reservoir at the top of the tank with a surface area of 6,000 m², partially excavated in rock and lined with concrete.
Construction of a concrete-lined expansion tunnel, 12 m in diameter and 200 m long.
Construction of three drainage culverts arranged along the perimeter of the surge tank at different heights, each having a cross-section of 3 x 4 m and a length of 225 m.
The drainage culverts are connected to an angled 240-m-high shaft with other variable-length tunnels having the same cross-section.
Consolidation drilling and grouting, anchor bolts for rock, test boring for control instrumentation.

MAIN TECHNICAL DATA:
Underground excavation: 1,300,000 m3
Underground concrete: 318,000 m3
Shoring: 10,000 t.
Centering: 4,000 t.
Reinforcing iron: 12,000 t.

Last update: 18/09/2013