This paper summarized the results of dynamic properties of the soil samples collected from one NPP site which is still under construction. Geotechnical aspects related with seismic safety of structures and foundation ground is important issues to be investigated. Recommendations and procedures given in IAEA Safety Standards Series No. NS-G-2.13 Evaluation of seismic safety for existing nuclear installations; IAEA Series No. NS-G-3.6 Geotechnical Aspects of Site Evaluation and Foundations for Nuclear Power Plants and US NRC Regulatory Guide 1.138 have been generally followed.

A series of strain controlled cyclic simple shear tests have been carried out on dry soil samples ranging from small-medium to large shear strain levels. Simple shear condition is the one of the most representative strain condition of in-situ ground during seismic event and very suitable for evaluating ground response. Laboratory testing using the Dynamic Simple Shear Apparatus with improved measuring devices were performed on samples taken from the site and the nonlinear stress-strain relationships were established. Stable hysteresis curves from the tests enable clear definition of G/Gmax-γ and D-γ curves which describe the apparent reduction of the shear modulus G and the variation of damping ratio D of the investigated soil samples within the shear strain range of interest.

Based on the results from the performed cyclic simple shear tests the relationship between the initial shear moduli versus overburden pressure for the current soil layers was established. The results gathered from laboratory investigations regarding the dynamic characteristics of soils are important step in the process of site response analysis and developing specific site response spectra to evaluate the seismic loading and earthquake geotechnical aspects of sub-surface soil layers. This study clarifies that cyclic simple shear tests on careful prepare soil samples give reliable results over wide range of shear strain and therefore can be primarily solution for laboratory investigation on dynamic properties of soil layers.

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