130. Geotechnical Assessment of Foundation for a Gravity Dam in the Lesser Himalaya of Jammu and Kashmir

The construction of the 900 MW hydroelectric project was taken up, after an investigating history of over 40 years. The geotechnical assessment for the 144.5 m high gravity dam, across Chenab river, is based on the results of explorations carried out through five drifts, over 1000 m of core drilling, four sets of in situ rock mechanics tests, geomechanical tests/material testing and test grouting, etc. The unweathered to slightly weathered quartzite, phyllitic quartzite with slates provides the foundation for the dam. The rock mass is greatly influenced by it's nearness to the Muree thrust. The joint volume (JV) of +20 gives rise to highly blocky to crushed rock mass showing a permeability of <10 lugeon.The moderately to highly weathered slate bands of 1–6 m width and a +24 m wide shear zone, sympathetic to the thrust, were treated based on Shasta's formula and FEM analysis respectively. The foundation has been consolidated and made monolithic by grouting for a depth of 15 m with a grout consumption of < 68 kg/m and the curtain grouting was restricted to a variable depth of 50% of the hydraulic head or three stages of < 5 lugeon permeability, based on trial grouting. The paper deals in detail the geotechnical evaluation of foundation for the gravity dam.