The construction of the inlet structure of the 11.0 m dia, diversion tunnel at Sykia dam site, designed also to serve as bottom outlet, included an 120 m high excavation in bedded limestone. Unfavorable orientation and poor mechanical characteristics of discontinuities of the rock mass led to the adoption of heavy support measures. Detailed geological interpretation, continual supervision and monitoring of the excavated surfaces, pointed areas of potential instabilities where appropriate support was applied. This paper presents the construction stages, and describes the adopted support and monitoring techniques.


La construction de I' entree du tunnel de derivation de dia, eagle a 11,0 m au site de barrage de Sykia, prevue de service abuse come evacuator de cure, comprenait des travaux d' excavation d'une hauteur eagle a 120 m dans une roche calcaire stratifiee. L'orientation unfavorable et les foibles caracteristiques mecaniques des discontinuitees ont conduit a I' adoption d' importants mesures de protection. L' interpretation geologique detailed et I' auscultation continue du comportement de la surface exclave ont permits de dueler des regions susceptible a des instabilities, aquarelles des mesures additionally de protection on ete prizes. La communication presented les tapes de construction eye decries les techniques, de soutennement et d' auscultation utilisees.


Ein Einschnitt von der Höhe von 120 m, in Rah men der Arbiter in Sykiadamm, wurde nötig fuer das Einlaufbauwerk des Umlaufund Entleerungstunnels, und war in geschichteten Kalkstein. Da die Orientierung der Schechter unguenstig war und die mechanischen Eingeschaften der Kluften des Felses auch sehr arm, hale dazu get hurl t zur Einrichtung von verhalt nissmassig starke Sicherungs masxnahmen. Durch detaillierte Analyse der geologischen verhaltnisse und standige Aufsicht warned des Pushups- Arbiter wurden die unsichere Platze erörtet und die nötige Massnahmen geplant. Diese Arbeit will die Reihefolge der Arbiter wahrend der Bau von Massnahmen zur Sicherung und Üherpruefung des Einschnittes Eigen.


Sykia dam is part of the Echelons river development scheme, a combined hydroelectric and irrigation project. It is a 150 m high earth dam, situated in Pintos mountains, Central Greece, planned to he built downstream of the already completed 150 high Messochora concrete faced dam. A 18 Km long power tunnel, starting from Sykia reservoir will drive water to the Pefkofyton Power station and furthermore to Thessaly plain. Sykia 11,0 m final dia., 1160 m long diversion tunnel is designed to serve also as bottom outlet and in order to accommodate it's inlet structure, a major open-cut excavation was executed at the steep right abutment of the river (Fig. I).


Geologically, Pintos is composed of folded and faulted sedimentary rocks mainly limestone, flysch, chert and shale. Site rock in particular, is Cretaceous Limestone and consists principally of thin to medium bedded grey or pink pelagic limestone, interbedded with chert and shale. Shale layers are usually sheared, slickenside and occasionally softened to clay. Although intensely folded, rock mass is of good quality with a moderate degree of fracturing. Weathering takes place only to shallow depths and along joint planes developing local caustic features. It should be stated that the formation had shown an excellent behaviour in tunneling. At the excavation site, the orientation of bedding is generally unfavorable and controls the stability of the slope in combination with:

  1. The presence and characteristics of shale interbreeds (thickness, water content, existence of prehearing, decomposition to clay)

  2. Rock relaxation and stress relief phenomena.

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