Grouting and drainage of the foundation of the concrete dam at the Zeya hydroelectric station

Abstract

The roundhead buttress dam for the Zeya hydroelectric station has a height of 112 m, crest length of 714 m, and volume of about 2,200,000 m 3 of concrete,Reservoir filling began in Aug. 1975 and the first unit was put under load in November.The dam is divided lengthwise into 44 sections of three types: fixed gravity and buttress at abutments, single buttress on the spillway part, and double buttress in the powerhouse part.Galleries for grouting and drainage, measuring 3.5x 3.5 m in section, are constructed at the base of the upstream column of the sections.The distance between axes of the galleries is 7.5 m. In the bank sections the grouting gallery is inclined with a stepped invert.The drainage gallery consists of individual horizontal segments.A Lower Paleozoic intrusion of diorites with veins of lamprophyres and porphyrites of Mesozoic Age form the foundation of the dam.The intrusion extends latitudinally as a band 5-6 km wide.The deep Pikan fault, the formation of which affected the preservation of the rock foundation, is the southern boundary of the rock mass.Six systems of tectonic fractures and zones were traced in the foundation pit during documenting of the site.The predominant strike of the fractures is northeast.In the area of the main structures there are 12 tectonic zones with a thickness of more than 0.5 m and in individual cases more than 3 m. The largest tectonic zone of meridional direction cuts across the axis of the dam in the region of spillway section No. 13. The thickness of the shattered and mylonitized rocks in the zone reaches 10-15 m, and the rocks at the contact with the zone are intensely fractured (Fig. i).A second large tectonic zone in the latitudinal direction with a 60-80 ~ dip toward the upper pool is exposed in the channel and flanks (zone No. 1-8).In the channel it passes i0-15 m from the upstream face of the dam and in the flanks cuts across the foundation in the regions of sections 3-6 and 36-40.A tectonic crack up to 0.5 m thick, filled with gouge, is traced along the entire zone.The blocky structure of the rock caused by the joints is mainly within 10-20 cm.The fracture voids ratio in the channel area is within 0.005-0.15% and in the flanks 0.5-1%.The diorite mass, as we see from the permeability profile (Fig. i) obtained by testing boreholes in the first stage of the grout curtain, is characterized mainly by specific water absorption values less than 0.05 liter/min.Zones of increased permeability are generally individual pockets confined to the largest tectonic fractures and extending to a depth of 30-40 m.Individual absorbing zones are found at a depth of 50-60 m, but we can consider that for depths over 60 m the foundation is practically impervious.The grouting and drainage work in the foundation of the dam* called for 36,000 linear meters of grouting and ii,000 linear meters of drain wells.The project included a deep grout curtain made up of two rows of drilled holes (20,700 m), stabilizing grouting in the foundation of the upstream column (8300 m) and grouting of the ...