Determination of the level of seismic danger and design seismic loads for large hydrotechnical structures

Abstract

Translated from Gidrotekhnicheskoe Stroitel 'stvo, No. 11, November 2005, pp. 16 -26. A local network of sensitive high-accuracy seismological stations has to be created for seismological observations near a hydrotechnical structure and on the banks of the storage reservoir. The layout of the network is chosen with allowance for the configuration of the reservoir and for the location of the seismogenerating zone relative to the structure.One of the most important aspects of provision of reliable operation of the power system of Russia is the improvement of its seismic stability and safety, because a considerable part of the objects of the power industry of Russia lie in regions of elevated and high seismic activity ( Fig. 1). Due to the insufficiently accurate determination of seismic conditions in the places of erection of these objects many of them have been designed for lower seismic loads than is stipulated by modern standards, which places them in the category of objects of enhanced potential danger. The highest social risk can be expected for hydrotechnical structures build in regions with complex geodynamic conditions characterized by high contemporary activity of seismogeological, tectonic, slip-andslide, karstic, boil, and other dangerous geological processes and phenomena.Despite the obvious progress in the possibilities of design, building technology, and methods of field control of the reliability of objects of the hydropower industry, earthquakes continue to cause emergencies with enormous losses and fatalities. One of the main causes of this phenomenon is underestimation of the seismic conditions at construction sites.In order to guarantee seismic resistance of large hydrotechnical structures the main tasks of seismological engineering research should be formulated as follows:-appropriate choice of the site and reliable determination of seismic conditions of the region of the future object including the background response characteristic of its seismic mode and evaluation of background design loads for design earthquake and maximum design earthquake;-determination of the effect exerted on the design parameters of seismic loads by the local seismological and morphological conditions of the construction site (special features of the structure and properties of the rock (soil) mass in the bed and walls of the structure, surface topography, constructional works, etc.); -control of changes in the seismic regime and local manifestations of seismicity in the process of erection and maintenance of the object; prediction of possible changes in the parameters of design seismic loads connected with changes in the properties of the ambient in the zone of influence of the reservoir (object); determination and study of the effect of induced seismicity;-measurement of the reaction of structures of the object to different-intensity seismic loads with the aim of correcting the results of computations of seismic stability and obtaining data for creating and calibrating a dynamic model of the "structure-bed-reservo...