ABSTRACT:
This paper describes the methodology of the design of large underground caverns in the Himalayan region of India. The design process involved continuous evaluation of rock parameters, detailed 2D and 3D numerical modeling and monitoring program. Hoek and Brown (1997).failure criterion was used to estimate the rock mass strength parameters for the model analysis and the model results validated with the field measurements.
RÉSUMÉ:
Cette communication-decrit la methodologie de la conception des grandes cavernes souterraines dans la region himalayenne de l'Inde. Le processus de conception implique l'evaluation continue des parametres de rochers, Ie modelage numerique à deux et trois dimensions et le programme de contrôle, Le critere d'echec de Hoek et Brown (1997) a ete utilise pour estimer les parametres de force de la masse de rochers pour l'analyse du modeleet les resultats du modele qui sont valides avec les mesures sur le terrain.
ZUSAMMENFASSUNG:
Diese Papier beschreibt die Methodenlehre des Musters von große Untergrundhöhlen in der Region des Himalayas, Indien. Die Zeichnungsprozeß verwickelte fortdauernde Abschatzung der Felsenparametern., ausfuehrliche 2D und 3D Zahlenmodelierung und Warnzeichenprogramm. Hoek und Brown (1997) Fehlenkennzeichen waren benutzt urn die Felsenkraftparameter fuer die analyse zu bewerten, und die Modelergebnisse bestatigen mit die Feldmessen.
INTRODUCTION
The Tehri Hydro Power Project is under construction at Tehri, U.P, India by J'ehri Hydro Power Corporation (THDC). The first stage of the project, planned to generate 1000 MW, includes a 260m high earth and rockfill dam across the river Bhagirathi downstream of Tehri town and underground powerhouse complex on the left abutment hill of the dam.
Numerical modeling coupled with instrumentation was the basis for design of the excavations. Combination of two- and three-dimensional modeling was ‘used’ for effective and optimized support design, FLAC, (Itasca, 1995a) was used for 2D analysis for design of pattern support system. Shear zones and major shear planes were modeled in 3D discontinuum analysis with 3DEC (Itasca, 1995b). Instrumentation scheme was planned and implemented to calibrate the model. This paper demonstrates the role of advanced numerical modeling technique in the analysis and design of the caverns.
POWER HOUSE COMPLEX
The powerhouse complex consists of two main parallel caverns namely the Machine Hall (MH) and the Transformer Hall (TH) located about 370m below the surface. The MH cavern is 188m long, 22m wide and 47m high. There are four turbine pits 16m deep on the floor of the machine hall. The TH cavern is 161m long, 18.5m wide and 36m high located upstream of the MH with a 41.75m rock pillar between them. In addition there are other excavation such as pressure tunnels, draft tubes, bus duct tunnels and adits joining the main caverns and drainage galleries.
The Tehri hydropower project is located in the Lesser Himalayas. The rock formation 10 the power house area is mainly massive to thinly bedded Phyllitic Quartzite with caverns oriented perpendicular to foliation strike direction. There are four major joint sets and several shear planes with varying thickness (Navani, 1996).
