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The foundations of the dam at the Krasnoyarsk hydroelectric plant consist of medium and fine-grained granites with veins of syenites, vogesites, and porphyrites 3-7 m thick, which intrude aloug a system of stecply dipping joints. The granites and vein materials are fractured by primary separation cracks. Tectonic disturbances are associated with such joints and cracks. In the dam foundations are gently sloping tectonic zones. The spatial orientation of these zones is unfavorable to the dam stability since the joints dip 7-20" toward the downstream side. These tectonic disturbances include zones of schistose and crushed granites with rabble pockets and seams, containing traces of clay materials.During 1964-1966, tests were carried out at the Krasnoyarsk hydroelectric plant on the shearing of two rock masses with a shearing area ofui) to 100 m S each [1]. To carry out these tests, one of the weakest portions of the dam foundations was selected, which is in the immediate vicinity of the downstream end of the dam (Fig. 1). There, within the limits ofsectiom 49 and 50, two rock pillars 8x 12 m in area and 7 m high were prepared. The pillars consisted of brownish-red, fine-grained, porphyrite-like, sound jointed granite.

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