The wide scope of comprehensive engineering investigations due to the complicated geological conditions of the Scheme area has been carried out for the designing of the Koteshwar Scheme in India. The article spotlights the basic results of executed engineering investigations and their interpretation.
En projetant de la station hydroeaectrique Koteshwar à l'Inde un grande volume des etudes geotechniques complexes à ete foit en raison de la situation geotechnique composee sur ce terrain. Dans l'article on regarde des resultats principaux et l'interpretation des etudes foites.
Im Lauf der Projektierung des Wasserkraft Koteschwar in Indien ist eine groβe Umfang der Ingenieurgeologische Forschungen ausgefuhrt, da die Ingenieurgeologische Verhaltnisse in der Sperrstelle komplieziert sind; Die Hauptsachliche Ergebnissen der ausgefuehrte forschungen sind betrachtet und interpretiert.
The Koteshwar Dam is designed on the Bhagirathi River in the Lower Himalaya. It is located at a distance of 20 km downstream of the Tehri HPC. The design envisages construction of the concrete gravity dam 97.5 m high with the reservoir storage of 89 million cu.m. The scheduled capacity of the power station - 400 MW. During the period from 1992 to 1994 the "Hydroproject" Institute has carried out the required scope of designing-engineering investigations as assigned by the Customer. The detailed engineering-geological, geophysical and geomechanical investigations at the dam site were carried out from December 1992 to February 1994. During the investigations Indian Company Thapar made some 2150 m of adits and fourty two drill holes, with total length of 3140 m.
The Bhagirathi River runs in a narrow rock gorge at the dam site. The third above flood plain terrace about 100 m wide is traced on the right bank slope about 100 m higher the water level. The distinguishing feature of the dam site is the buried river bed under the terrace deposits. The Quaternary deposits are represented in this area by recent river bed alluvium of small thickness, rather thin colluvium-deluvium on the slopes and ancient alluvium in the buried river bed about 50 m in thickness. The foundation of the main structures con- Sists of the Upper Proterozoic metamorphic rocks: phyllites, quartzitic phyllites and argillaceous (metamorphic processes transformed clay minerals into mica) phyllites. All these lithotypes are rythmically alterated, forming the rhythms from several rom to dozens of meters in thickness. The quartzitic phyllites predominate at the base of rhythms and argillaceous varieties at the roof. The two types of benches are distinguished, accounting for the predominating petrographic composition: "quartzitic phyllites" and "argillaceous phyllites". The twenty four benches with thickness from 50 m to 100 m were traced during geological mapping of the area for the main structures. The area is featured with the very complicated folding structure, represented by a number of subparallel overturned forlds. Their axes planes are at about 200 m from each other and dips to the NE at an angle about 30°, thus, close to the schistosity orientation. The foundation and abutments of the designed dam belong to one fold wing with steep bedding (dipping azimuth 145–165° and angle of dipping from 40° to 50° in the low parts of the slope, and to 65° -85° in the upper. The increase of slope steepness with its height is most probably due to the approach to the other wing of the fold. The orientation of schistosity being subparallel to the axes planes of folds confirms its origin in connection with folding and allows to name it as cleavage.
