Condition of potentially unstable rock masses in the left-bank slope during construction and operation of the Sayano-Shushenskoe hydroelectric power plant

Abstract

1. In connection with the fact that potentially unstable masses exist in the immediate vicinity of the dam and powerhouse, which are referred to as Class I structures in terms of capital expenditures, the approach taken for the design of PUM stabilization should be nonstandard with consideration given to a number of permanent vibratory design loads introiduced by operating hydraulic units and spillways, as well cyclically varying loads due to the weight of the water in the reservoir and the weight of the structures. 2. It is proposed to define the volumes required for PUM stabilization of the left-bank slope more precisely on the basis of observations of PUM during construction and operation of the hydroelectric plant. The interruptions that have occurred in the instrument observations should therefore be recognized as impermissible. 3. Construction and operating experience has demonstrated that it is expedient to perform work on stabilization of potentially unstable masses prior to the start of construction on entities located in their immediate vicinity. 4. A protective rock wall built at the foot of the slope cannot provide for the complete safety of the structures located close to the left-bank slope during the collapse of rock blocks or individual stones. 5. On-going monitoring of the condition of the left-bank slope does not correspond completely to problems of providing for the safety of the structures and personnel at the hydroelectric plant by reason of the low reliability of the measuring equipment. 6. Use of the automated “Relos-L” system for observations of the condition of the rock masses will make it possible to carry out continuous on-going monitoring within the framework of the automated production-control system at the Sayano-Shushenskoe hydroelectric plant. Only a multifunctional monitoring system, which includes different kinds of independent observations, can provide a sufficiently valid evaluation of the state of the PUM, and, on their basis, determine measures to prevent possible emergency situations. 7. The collapse of PUM in the initial stage of construction with subsequent plaining of the slope and the organization of multistory rock-entrapping benches is a more reliable, safe, and, probably, economical (if expenditures for future operation are assumed in the calculation) method than their stabilization.