The Siah Bishe Pumped Storage Project is now under construction. The investigation results, the stability analysis and the support concept for the cavern are reported. The powerhouse is arranged in sedimentary and volcanic rocks of Permian age. The frequency and width of bedding parallel shearzones determined the final support concept. The results of stability analyses show distinctly asymmetrical overstressed zones.


La centrale hydroelectrique de Siah Bishe est actuellement en construction. Les resultats des investigations, les analyses portant sur la stabilite des ouvrages ainsi que les etudes de soutènement sont decrit. La centrale est situee dans les roches sedimentaires et volcaniques permiennes. Le concept definitif de soutènement de la caverne est determine par les espaces et les epaisseurs des zones de cisaillement en couches Parallèles.


Das Pumpspeicherkraftwerk Siah Bishe wird zur Zeit gebaut. Die Untersuchungsergebnisse, die Standsicherheitsanalyse und der Sicherungsentwurf fuer die Kaverne werden beschrieben. Das Krafthaus liegt in Sediment- und vulkanischen Gesteinen des Perm. Die Abstande und die Dicke der schichtparallelen Scherzonen bestimmen die endgueltige sicherung.


Lahmeyer International was entrusted 1983 with the design of the 4 X 250 MW Siah-Bishe Pumped Storage Scheme. The waterways of the plant are now under construction (see fig. 1). It is located in the northern part of the Alburz Mountain, at a distance of 80 km from the Caspian Sea. The pumped storage plant is situated in layers of the Jurassic Shemshak formation and in the strata of Permian age called Ruteh, Nesen and Dorud formation. The Gamrudbar thrust fault separates the Jurassic Formation from the Permian one. This formation consists of shaly, slightly sandy siltstone, quartzitic sandstone and intrusions of igneous rock such as spilitic basalt partially bedding parallel orientated and massive Dacite. The whole formation is folded and forms the southern flanc of an anticline. The folding process caused a shearing of incompetent layers such as thin layers of siltstone between sandstone beds but also between siltstones with different content of fines like clay or fine sand.


The area of the underground powerhouse was investigated by the excavation of four test adits in total 700 metres long, by underground drillings of 1776 m, i.e. 31 boreholes with an average length of 57,6 m per hole. Figure 2 shows the arrangement of investigations. The boreholes were drilled in various directions and with different inclinations. Dilatometer tests as well as permeability tests have been performed in selected boreholes. The access adit with a length of about 310 m runs diagonally to the strike of the layers of the Dorud formation, mainly in massive limestones over the first 160 m, after that follow siltstones and sandstones and at the tunnel end Dacite is exposed. This exposed rock sequence has been geologically mapped, the discontinuities as joints and bedding planes have been evaluated and according to these results a portal was fixed for a cavern roof adit considering all other aspects such as lengths of tailrace tunnels, inclination of pressure shafts and the rock overburden above cavern roof. The excavated roof adit had a length of 196 metres. The first 50 m were inclined by 100 in order to reach the elevation of 1882 m which was 5 m below the cavern roof.

3.1 Bedding

The roof adit exposed a rock sequence with a mean strike and dip of bedding planes of N 98°E/60°W up to station 120 m where a fault crossed the adit. The following rock sequence was striking parallel to the direction of the adit.

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