V_S and N_SPT Measures for Seismic Characterization of Soils

Abstract

Seismic classification of soils for designing purposes can be addressed by means of the measurements of shear wave velocity along thirty meters (V_S30) according to the new Italian building code and Eurocode 8. Alternatively, especially for granular soils, the number of blow counts from standard penetration tests (N_SPT) can be used at this aim. Although the nature of the two testing methods suggests not to relate small to large deformation measurements, corresponding V_S and N_SPT ranges of values are proposed by technical codes. A wide survey based on V_S and N_SPT measures (among others) has been performed in the most hazardous areas of Tuscan Region. There, within the VEL project (Local Seismic Effect Assessment), financed by the Tuscan Office for Seismic Prevention, a large dataset of 892 pairs of the V_S and N_SPT was collected. These pairs are here compared with the seismic soil categories introduced by Italian and European codes. The evident inconsistencies from the measured pairs and the code categories suggest not to rely on N_SPT values for soil characterization by means of V_S30.