DESIGN CONSIDERATIONS FOR VISHNUGAD PIPALKOTI DAM IN HIGHLY SEISMIC ENVIRONMENT

摘要

Alaknanda River in the Himalayas, a major tributary of holy river Ganga, has steep bed slope which is quite suitable for harnessing its hydro-power potential by way of constructing run-off-the-river or storage schemes as per the site conditions. Vishnugad Pipalkoti HEP, situated in the Chamoli district, Uttarakhand, is proposed to harness the hydro-power potential of the Alaknanda River by way of construction of a 65 m high concrete gravity diversion dam across it near a village Helong. It envisagesa drop in water level from 1267 m to 1027 m over a river stretch of about 31 km from village Helong to village Birahi. The net rated head of water for generation of power will be about 212.46 m. River water shall be diverted through an underground waterconductor system to an underground powerhouse (installed capacity - 444 MW) located near village Haat. The project area lies within the Zone V of the Seismic Zoning map of India (IS 1893 Part 1,2002) and is very close to the Main Central Thrust (MCT).During the initial stages of the design, section of the dam was finalised after carrying out a pseudo-static analysis. However, for the Tender stage design, in view of high seismicity of the area, a detailed seismic analysis of the dam-foundation systemhas been carried out so that the likely zones of tension within the dam section are identified and appropriate design measures are taken during the construction. A number of preventive design measures have been specified for ensuring the safety of dam and its foundation during its service life. This paper provides an insight into the various design considerations made for the dam.