SPT blow count vs. shear wave velocity relationship in the structurally complex formations of the Molise Region (Italy)

The relationship between the shear wave velocity (VS) and the blow number of the Standard Penetration Tests (NSPT) was investigated with reference to the structurally complex formations located in a wide sector of the Southern Apennine chain (Molise Region, Italy). Novel NSPT–VS correlations were developed, based on a balanced number of in situ tests coming from the seismic microzonation of the municipalities of Campobasso District and the seismic vulnerability assessment of strategic road infrastructures. It was proven that available relationships were not able to fit the data in the area of interest, even making the analysis according to the soil grain size classification. This circumstance was related to the nature of the geological formations, which are chaotically built and affected by complex structural–textural and lithological characteristics. Hence, in this paper, a rational methodology for an integrated geological and geotechnical assessment of the available field data based on lithostratigraphical features was presented and discussed. Three original empirical NSPT–VS power function relationships were derived and distinguished depending on the main lithofacies recognized in the Campobasso District, corresponding to Structured Soil Deposit (SSD), All Soils (AS) and Weathered Soils (WS). Their validation through statistical assessment of data confirmed the relevance of the results and the advantages related to their use at regional scale, based on an integrated geological and geotechnical approach.