Cyclic simple shear and triaxial tests on Lisbon Region liquefiable sands

The Lower Tagus River Valley area, in Lisbon, Portugal, has been studied for having a high potential liquefaction risk, due to the geological and geomorphological settings and the seismicity associated to the region. This study focuses on the comparison of the cyclic behaviour of three sands collected on site, using two distinct laboratory procedures. Tests with different values of Cyclic Stress Ratio were conducted in both cyclic simple shear and cyclic triaxial testing apparatus to assess the CRR curves of each material in reconstituted conditions. The comparison of the results highlights the main differences caused by distinct cyclic loading stress paths especially in view of the results when inversion or rotation of the principal stresses are induced. The tests also investigate the influence of the fines content and the cycling frequency in the number of cycles required for liquefaction to occur, while discussing the criteria for limit/instability level