The paper deals with problems of concrete dams rock foundations safety: statistics of failures and use of obtained information in safety analysis as well as the results of geomechanical investigations into the rock foundations properties.
The safety of structure is ensured in of existing structures and upgrading investigations, surveys, construction the safety criteria, of elaboration and operation periods by employment of new methods of investigation, of experience accumulated in the past by adequate safety criteria. Extensive potentialities of the engineering practice have been attested to by the successful filling of the Inguri Dam storage reservoir, 1.03 cub. Km in storage capacity, in August,1987. The resulting load on the highest arch dam of the world amounted 9.8 mill. t. Nevertheless the dam failures still are occurring. E.g.,rupture of 11 Small dams in USA in October, 1986, caused by a flood of 0.2 per cent probability (the design probability being 1.0–0.5 per cent) in the foundation grouping was estimated to be 141 mill. doll. Investigations into the mechanism of possible failures is too of importance for such small dams as the Sargazon embankment dam impounding a storage reservoir, 3mill. m3 in storage capacity. The dam rupture has resulted from the dam crest overtopping due to clogging of water outlets by mudflow materials.
Accound for actual cases of limiting and beyond-the-limit conditions in the practice of designing is one of the possible ways of improvement of decreasing the failures risk, developing more economical designs of structures. However to be employed in the safety analysis and in the structures designing the information on the failure cases is to be differentiated in respect to external forces, the structure capacity to resist and to properties of the structure members. Various "errors" of speacialists made in the mentiod above terms should be considered from the standpoint of the possible effect of them on the elements of the "environment-structure" system which is under the specialist control. The safety of the structure may be impaired, for instance, in the case the operator will not raise the spillway gates in good time and the dam is overtopped. The "structure" system safety may be impaired more gravely if some kinds of required investigations are neglected in the design studies, this resulting in a considerable underestimation of the external actions on the structure or in structure resistance.
Concrete dams on rock foundations are characterized by a high degree of safety featuring Longevity, trouble-free service and maintainability. The criteria of dam safety were formed in The course of more than 30 centuries of the dam building practice evolution. According to Data of ICOLD, the total risk of dam failures is 7.5×10−2(Deterioration…1984), the risk of failures of concrete dams on rock foundation during the dam service life (according to data of the Author) is 3.8xl0–2, the risk of complete failure being 2.2xl0–3
These data may characterize the level of dams safety in comparison with the level of risk of failures of other types of structures and the risk of natural calamities.