Yamuna Hydel Scheme Stage II in district, Dehradun of Uttar Pradesh, India was the maiden attempt of executing underground works of complicated nature in the young Himalayan rocks, generally of poor to very poor quality. This scheme has been implemented in two parts. The head race tunnel of Part II of this scheme traverses through over-stressed rocks of Nahan, Subathu and Mandhali formations separated by Nahan and Krol thrusts (intra-thrust zone) and three tear faults. To monitor the rock behaviour in intra-chrust zone an intermediate adit (inspection gallery) and an observation gallery parallel to the main tunnel was constructed in this zone. Different types of instruments were installed in these galleries for the purpose. Analysis of the observed data from the various instruments have revealed satisfactory behaviour of this zone. Further observations are continuing to keep a close watch on the behaviour of this zone.
Le projet de Yamuna Hydel Scheme Stage II dans le district de Dehradun de l'Etat de Uttar Pradesh en Inde, est la première entreprise des travaux souterrains d'une nature très complèxe dans Ie terrain rècent d'Himalaya, engènèral, de qualitè faible à très faible. On a exècutè ce projet dans deux phases. Le tunnel à l'eau à pression de partie II de ce projet se traverse par les roches sur-chargees de Nahan, Subathu et des plateformes de Mandhali separees par des poussees de Nahan et Krol et des trois defauts lactymères. Afin de suivre la nature de la roche dans la zone intra-poussee, on a construit une galerie intermediaire et une galerie d'observation parallele au tunnel principal. De differentes sortes des instruments etaient etablis dans ces galeries pour cet objet. L'analyse des periodes observees auprès de divers instruments a indique une nature satisfaissante de cette zone. Encore des observations sont en train de surveiller la nature de cette zone.
Der Yamuna Hydel Plan Stufe II im Bezirk Dehradun, Bundesland Uttar Pradesh, Indien war der erste Versuch komplizierte, untergrundliche Arbeit in den jungen, himalaiischen Gesteinen zu erledigen' diese Gesteine sind normalerweise von arm bis sehr armer Qualitat. Dieser Plan wurde in zwei Teilen verwirkiicht. Der Hauptrenntunnel von Teil II dieses Plans durchquert ubergedruckte Gesteine von den Nahan, Subathu und Mandhali Formationen, die durch die Nahan und Krol Drucke (innere Druckzone) und drei Rissfehler getrennt sind. Ein Zwischenbereich (Untersuchungsgalerie) und eine Beobachtungsgalerie, die dem Haupttunnel parallel laufen, wurden in der inneren Druckzone gebaut, um das Gesteinenverhalten in dieser Zone zu steuern. Um diesen Zweck zu erfuellen, wurden verschiedene Sorten von Instrumenten in diesen Galerien installiert. Eine Analyse der beobachteten Daten der verschiedenen Instrumenten zeigt zufriedenstellendes Verhalten in dieser zone. Weitere Beobachtungen werden gemacht um das verhalten hier eng zu untersuchen.
Yamuna Hydel Scheme Stage-II in district Dehradun of Uttar Pradesh, India is a run-of-the-river hydroelectric scheme envisaging utilization of a total drop of 186 m in river Tons, a major tributary of river Yamuna which flows along a circuitous route forming S-curves, which have been cut across to make available the drop for generation of power by constructing a long water conveyance system of 7.5m diameter tunnels. A study of the geological features along the alignment of the proposed tunnel had indicated adverse geological features in some length of the alignment which, it was apprehended, could result in delay of the completion of the work if the entire scheme was implemented in one stage. Hence the scheme had been decided to be implemented in two parts. Part I of the scheme utilizes a drop of 124 m by constructing a 60 m high concrete diversion dam at Ichari across river Tons, 6 Km long 7.5 m diameter lined tunnel and an underground power house at Chibro with an installed capacity of 240 M.W. The outlet discharge from the draft tubes of Chibro Power House is led through another 6 Km long tunnel system upto Khodri Power House to utilize the balance drop of 62 m to generate 120 M.W. power at a surface power station. The paper mainly deals with part II of the scheme the details of which are given in fig.1.
The head race tunnel of the scheme passes through the rocks of Nahan, Subathu and Mandhali formations separated by Nahan and Krol thrusts (intra-thrust zone) respectively as shown in fig. 2. Three tear faults F1-F1, F2-F2 and F3-F3 were also encountered in the tunnel alignment. The Mandhali rocks are exposed at the northern end of the tunnel while the Nahan rocks are exposed at the Southern end of the tunnel.
