V S profile: measured versus empirical correlations—a Lower Tagus river valley example

Abstract

During the last decades, there has been an increase in the use of geophysical tests for geotechnical characterization. The relatively low cost and the large volume analysed by non-invasive geophysical testing makes them very attractive for a site investigation plan combined with borings and other geotechnical tests. In some countries, for instance Portugal, the use of multichannel analysis of surface waves (MASW) and other surface wave methodologies is still limited. This work shows results obtained with the use of MASW in the geotechnical investigation of the foundation soils of a viaduct and a bridge, part of the IC3 route, with a total length of about 10 km. The study area is located very near the “Lower Tagus valley” active fault and above thick alluvial deposits. Comparisons of MASW with other in situ tests show that the results are in good agreement. The N(SPT)-V S correlations are still in use worldwide for practical purposes, but not always considering all the important parameters as the standard penetration test (SPT) energy measurement. In this paper, we discuss the usability of empirical correlations to obtain the shear wave velocity from SPT results, using the results from the case study presented. The large variability of results obtained proves the importance of measuring the shear wave velocity with geophysical tests.