EVALUATION OF CYCLIC LIQUEFACTION RESISTANCE FROM LABORATORY TESTS ON LIQUEFIABLE SOILS FROM THE LOWER TAGUS VALLEY

In mainland Portugal, seismic risk is particularly relevant in the south-west and south costal zones, mainly
in the Tagus River Valley and the Algarve region. The Lower Tagus Valley (LTV) has been affected by several earthquakes throughout history and also recently, which have caused serious material damages and loss of human lives. This area has been studied for its high susceptibility to the liquefaction phenomenon due to its geological and geomorphological conditions and the seismicity associated to the region. Within the scope of the European research project H2020 LIQUEFACT and the national project supported by FCT, Liq2ProEarth, a pilot site was selected in Lezíria Grande de Vila Franca de Xira, where a vast set of in situ tests were carried out and undisturbed samples were collected for later characterization in the laboratory. The performance of laboratory tests in these materials is determinant for the evaluation of its geomechanical behaviour in different seismic action scenarios and consequent definition of the necessary model parameters used in numerical analyses to evaluate the behaviour of the land with liquefiable soils in the event of an earthquake. The study presented in this article focuses on the comparison of results obtained by different test procedures performed on different materials collected in the experimental site. Cyclic triaxial tests, with inversion of principal stresses, and cyclic simple shear test, which allow the rotation of the principal stresses, were performed with different values of Cyclic Stress Ratio (CSR), whose objective was the determination of liquefaction susceptibility curves for each material. The tests investigate the influence of fines content and seismic action (characterized by CSR) on the behaviour of soils subjected to cyclic loading.