Analysis of the present stress-strain state of the arch-gravity dam at the Sayano-Shushenskaya HPP

Abstract

The present analysis is dictated by the need to assess the present condition of the arch-gravity dam at the Sayano-Shushenskaya HPP (SSHPP) in connection with a failure that had developed at the power plant and was followed by shutdown of all 10 generating sets, and by the need to pass drawdown flows through the spillways in the body of the dam. This situation placed the dam under special unforeseen operating conditions with use of spillway openings in the body of the dam during the winter.The stress-strain state of the dam and its bed, which had been caused by hydrostatic load and temperature, has been analyzed, and the dynamics of irreversible (residual) displacements of the dam exposed based on analysis of available data derived from previously conducted investigations, and also observations performed right up to February 2010 by the monitoring service GTS at the SSHPP. Brief HistoryConstruction of basic structures at the SSHPP was begun in 1968, and had been completed for the most part by the close of the 1980s. The dam was constructed under a partial head in 1978, and since 1990 had begun to operate in the design regime with annual filling of the reservoir to the normal backwater level (NBL) of 540 m, and with subsequent drawdown to the minimum operating level of 500 m.In terms of the combination of their basic parameters, the arch-gravity dam at the SSHPP has no analogies in world practice, and is one of the world's largest: it is 242 m high, the length along the crest is 1074 m, the width along the crest 25 m, and the width at the base 106 m. The maximum head is 220 m [1].For such a relationship between parameters of the structure, zones of loosening under the upstream face of the dam should have been expected to appear; this had also been confirmed by analytical and model investigations conducted as early as the detailed-design stage. In connection with the formation of a zone of loosening, the upper part of the grout curtain was found disturbed, resulting in a significant increase in seepage flows [2 -4].After the reservoir had been filled in 1989, it had become obvious that parameters of the stress-strain state of the dam exceeded values specified in the design. Horizontal tensile cracks appeared on the thrust front of the dam, and a disturbance was noted in the contact between the bed and thrust front of the dam. Filtration through the concrete of the dam and through the bed had reached 458 and 550 liters/sec, respectively. The absence of bottom discharges did not permit emptying of the reservoir, and it was therefore necessary to restore impermeability under a head of more than 200 m.The level of filtration did not make it possible to use traditional grouts for injection. Personnel at the hydroproject, together with specialists from the Lengidroproekt and the French firm Soletange, therefore developed a new procedure for repair operations using epoxy grouts, which was utilized for sealing cracks in both the body of the dam, and also in its rock bed during the period from 1996 through 2002. As a result...