Assessing the Effectiveness of Soil Parameters for Ground Response Characterization and Soil Classification

The average shear wave velocity over the top 30 m of a soil profile (_VS,30) represents an usual parameter for soil classification in a modern building code for seismic design. In this work the ground response of about 100 soil profiles in Tuscany and Molise (Italy) is studied through 1-D numerical simulations in order to evaluate the reliability of European and Italian soil classifications based on the _VS,30 criterion. The amplification factor, _Fa , defined here as the ratio of the pseudo-velocity response spectrum intensity (Housner 1952) at the surface, S ^Is , to the pseudo-velocity response spectrum intensity at the rock outcrop, S ^Ir , is related to some soil parameters, such as _VS,30, the fundamental frequency of vibration of the soil column, _F0, and seismic impedance contrast, _Iw . Analyzing the standard deviation of the residual obtained from regression analyses of _Fa versus _VS,30, _F0, and _Iw shows that _F0 is the most helpful parameter for the prediction of _Fa . Hence _F0 appears to be more appropriate than _VS,30 and _Iw for the characterization of the seismic response of a site and, therefore, should not be disregarded in building code soil classifications.