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 (V-S,V-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 V-S,V-30 criterion. The amplification factor, F-a, defined here as the ratio of the pseudo-velocity response spectrum intensity (Housner 1952) at the surface, SIs to the pseudo-velocity response spectrum intensity at the rock outcrop, SIr, is related to some soil parameters, such as V-S,V-30, the fundamental frequency of vibration of the soil column, F-0, and seismic impedance contrast, I-w. Analyzing the standard deviation of the residual obtained from regression analyses of F-a versus V-S,V-30, F-0, and I-w shows that F-0 is the most helpful parameter for the prediction of F-a. Hence F-0, appears to be more appropriate than V-S,V-30 and I-w for the characterization of the seismic response of a site and, therefore, should not be disregarded in building code soil classifications.