Estimated versus measured Vs profiles and Vs30 from geotechnical and geophysical tests at a pilot site in the lower Tagus valley, Portugal

A pilot site in the Lower Tagus Valley near Lisbon, in Portugal has recently been set-up for liquefaction susceptibility analysis and microzonation, within the scope of the European H2020 LIQUEFACT research project. A comprehensive geological, geophysical and geotechnical site investigation campaign has been carefully carried out, including SPT, CPTu, SDMT and geophysical methods, as well as high-quality soil sampling for laboratory characterization. The geophysical tests comprised seismic refraction, SASW and borehole seismic tests (SDMT), among others. For the definition of the VS profiles and respective VS30 values, two approaches were followed: 1) predictions from geotechnical tests; 2) direct VS measurements. Considering the detailed geotechnical field data obtained in the SPT, CPT and DMT tests, VS profiles and VS30 have been estimated, based on different proposals available in the literature. The direct measurements of VS extracted from SDMT, as well as from seismic refraction and SASW geophysical tests, were subsequently integrated for comparison with the estimated values. This paper will focus on the comparative analysis of the estimated versus measured results, discussing on the reliability and adequacy of VS estimates based on the existing proposals, considering also the type of test (SPT, CPT or DMT) used in the predictions.