Page - 1119 - in Book of Full Papers - Symposium Hydro Engineering

Methodology Major seismic input parameters for SSA are: PGA, duration, site- independent (standard) response spectra and acceleration time-histories. The horizontal PGA in accordance to the SEE return period is derived by means of an empirical intensity-acceleration equation and based on seismic hazard maps (isolines of MSK intensity) published in 1977 [6]. The derived PGA becomes the scaling value of normalized subsoil class- dependent standard response spectral shapes [7] which simultaneously act in the two horizontal and in the vertical directions. Vertical PGA is computed as 2/3 of horizontal PGA. For Flumenthal and Ruppoldingen, PGA of 0.155 g (duration 13 s) and 0.17 g (duration 14s) are considered respectively. Geological conditions of riverbeds are usually characterized by a sequence of gravelly, sandy, silty layers above sound bedrock. Therefore, site-dependent response spectra needed to be evaluated at Ruppoldingen HPP (Fig. 2). The presence of a 5.5 m thick fully saturated sand layer above bedrock with averaged granulometric curve with good fit into potential liquefiable sands required evaluation of liquefaction potential based on SPT tests outcomes, available from the geotechnical investigations performed during the construction time (Fig.3). Fig. 2 SSA performed with site-dependent response spectra below weir foundation and below powerhouse foundation on bedrock at Ruppoldingen HPP 1119