Geotechnical Suitability of Tehri Dam Site, Uttarakhand, India

Construction of a high earth core rock fill dam at Tehri is a first major attempt to tap the immense hydropower potential of Bhagirathi River. This multipurpose mega hydro electric project envisages generation of 2400 MW (IC) of hydroelectricity in two stages and after completion of both the stages it will add 6200 million units of electricity to the northern grid.

The project site, located in Garhwal Lesser Himalaya, exposes phyllites and its arenaceous variants of Chandpur Formation, Jaunsar Group (Proterozoic-III). The phyllites at the dam site were classified into phyllitic quartzite thinly bedded (PQT), phyllitic quartzite massive (PQM), quartzitic phyllite (QP) and sheared phyllite (SP) and they are characterized by seismic wave velocity (Vp) of 5.5–6.0 km/sec, 4.5–5.3 km/sec, 3.0–3.5 km/sec and 1.5–2.0 km/sec respectively. The location of such a big rock fill structure in geodynamically active, seismically sensitive and geologically fragile Himalayan region has always invited pessimism, however the advantages provided by this site, and the site response during and after the construction, has dispelled all the nihilism.

The performance of the main dam and appurtenant structures has been actually tested with the real time monitoring system. The total seepage, from different galleries is far less than 1 cusec and considering the size of the reservoir is negligible. The dam body is stable and all zones of the dam, as such, are functioning well.

In the spillways, no instrument has recorded abnormal values in any of the structures which indicate its stability and efficient functioning. Convergence in the common wall between machine hall and transformer hall is stabilised after achieving a maximum of 21.60 mm. The paper discusses the suitability and viability of Tehri dam site by providing a detailed, yet critical review, from the point of view of geological disposition, seismotectonic set up and geotechnical evaluation during and after the construction of the project. Introduction behind a 260.50 m high earth core rock fill dam, in a reservoir spread of 42 sq. km. The stage II of the project