The geotechnical test site in the greater Lisbon area for liquefaction characterisation and sample quality control of cohesionless soils

Abstract

In the greater Lisbon area, widespread alluvial sandy deposits can be found that, due to its geology, geomorphology and high seismicity satisfy the criteria to trigger soil liquefaction if subjected to a cyclic action. Within the scope of a research project on liquefaction (LIQ2PROEARTH), an extensive geological, geotechnical, and geophysical database was established, including specific site investigation campaigns in four testing locations, in the municipalities of Benavente and Vila Franca de Xira, near Lisbon. In particular, the campaigns focused on the performance of SPT, CPTu, SDMT and geophysical tests, as well as on the collection of high-quality soil samples using advanced sampling techniques. This paper addresses the geotechnical characterization of a test site and describes the advanced sampling processes for liquefaction assessment. High-quality samples were retrieved by means of three different samplers: Mazier, Dames & Moore and Gel-Push. Preliminary assessment of the sampling quality of the collected samples has been made through the comparison of normalised field and laboratory measurements of shear wave velocity, emphasising the divergences between the different samplers. A comparative analysis of the results is presented and discussed, highlighting the identification of the layers with higher liquefaction susceptibility.