Settlement from Seismic Compression at a Vertical Array near a Nuclear Power Plant

Strong ground motions from the Mw 6.6 2007 Niigata-ken Chuetsu-oki earthquake were recorded by a free-field downhole array installed near the Service Hall of the Kashiwazaki-Kariwa nuclear power plant site. At the vertical array, a reconnaissance team observed ground settlements of up to 25 cm, which was later corroborated from a 2009 site investigation. Field tests suggested relative densities of approximately 30-40% in the upper sand layer which overlaid clayey bedrock. Samples from the site investigation were used to develop a material specific volumetric strain material model for the corresponding relative density. Using results from ground response analyses and the volumetric strain material model, ground settlements of approximately 13 cm due to horizontal shaking only were estimated. The estimated settlement increases to 19 to 20 cm when vertical ground motions are also considered. This range of settlement from seismic compression is in close agreement with the observed settlement near the site.