Site effect determination at liquefiable sites

Soft surface sedimentary layers can considerably increase damages during earthquakes. This soil amplification can be computed with different analytical methods. At loose saturated sandy layers, where pore pressure increase and liquefaction are probable, the effective stress method is the appropriate tool to compute site response. Some examples of computations are presented herein for the site of the Paks NPP, showing the effects of pore pressure increase to shear stress, strain and surface acceleration. The peak ground accelerations (PGA) computed with different methods has also been compared for different bedrock acceleration levels and it is shown that the results diverge with growing acceleration levels. For this soil profile differences appear first between linear and nonlinear methods at about 0.1 g, then between linear and equivalent linear methods at about 0.15 g and at last, between nonlinear total and effective stress methods at about 0.3 g. But application of the effective stress analysis may be necessary at lower acceleration levels under unfavourable site conditions. To delineate these areas, a preliminary liquefaction hazard map of Hungary has been constructed