SHEAR WAVE VELOCITY-PENETRATION RESISTENCE CORRELATION FOR HOLOCENE AND PLEISTOCENE SOILS OF AN AREA IN CENTRAL ITALY

ABSTRACT: With the aim of preventing and reducing the seismic risk in an area in Umbria, central Italy, of notable importance from a historic and economic point of view, the local government of the Umbria Region promoted a considerable seismic microzonation project. A widespread geotechnical investigation survey was carried out to this end, including sounding with undisturbed sampling, standard penetration tests, dynamic cone penetration tests, cone penetration tests, down-hole and cross-hole tests. The purposes of this paper are to summarise the results from field and laboratory testing performed to identify the main soil types detected in the area and to provide some empirical relations to estimate shear wave velocity from cone penetration re-sistance for the most representative geological formations of the region. With the aim of obtaining relationships that are as reliable as possible, the available data were carefully se-lected. Moreover, as it is well known that larger coefficients of determination are generally obtained when soil type, geologic age and sedimentary environment effects are considered in the regression equations, the selected data were subdivided and attributed to the two main geological units (Holocene and Pleistocene) pre-sent in the area. For each of these, grain size was classified using CPT data and two soil types (fine and coarse grained soils) were therefore identified. Regional correlations between shear wave velocity and pene-tration resistance parameters were thus assessed for all the four previously defined soil classes and for the two geological units without distinguishing fine-grained and coarse-grained soils. The proposed relationships were compared with those suggested in the geotechnical literature by different au-thors and their predictive capacity was finally checked by comparing VS values estimated by means of the correlations and those measured in geophysical survey (cross-hole and down-hole tests). The results of these comparisons are also shown in this paper.