Estimation of soil displacement profile for seismic design of underground structures in shallow soil

For the earthquake design of underground and basement structures, soil displacement needs to be predicted. In the present study, simplified methods for the prediction of soil period, damping ratio, and soil displacement profile were studied. First, existing methods for the estimation of site periods (in the elastic range) were applied to 440 actual soil profiles, and accuracy was evaluated by comparing the predictions with the site periods calculated by the wave propagation theory. The result showed that the simplified Rayleigh method and eigenvalue analysis showed better predictions. Then, modification coefficients for the inelastic site period and equivalent damping ratio (i.e., the effect of inelastic soil properties) were proposed based on the results of an equivalent linear site response analysis (SRA). Finally, a simplified method for the prediction of soil displacement profile was proposed. The proposed method was applied to 440 soil profiles, and the predicted soil displacement profiles agreed with the SRA results.