THE SPECIFIC DEVIATORIC ENERGY TO LIQUEFACTION IN SATURATED CYCLIC TRIAXIAL TESTS.

Within the European project LIQUEFACT, cyclic triaxial tests were carried out on an Italian sand, Pieve di Cento sand, taken from a field trial located in Emilia Romagna (Italy), which was affected by liquefaction during the 2012 earthquake. The cyclic resistance curve of that sand was obtained in laboratory on reconstituted specimens with a low confining stress and a low relative density to simulate the natural conditions in field. Based on an energetic model to predict the resistance to liquefaction of unsaturated soils, the role of the specific deviatoric energy to liquefaction (Es,liq) has been investigated for saturated soils. For each test the specific deviatoric energy (Es) has been evaluated with number of cycles and compared to the results of tests on fully saturated sandy soils (Leighton Buzzard, fraction E and Sant’Agostino sand) already published. The specific deviatoric energy increases with number of cycles until liquefaction and the maximum gradient of this curve seems to correspond to the attainment of liquefaction, according to stress criterion (excess pore pressure ratio, Ru = 0.90), save for the tests with a lower Nliq. Moreover, it has been noted an interesting dependence from the number of cycles at lique- faction, which seems to be independent from the cyclic deviatoric stress applied and the state of soil, at least in the range of confining stresses (σc’) and relative densities (Dr) considered in this research (50<100 kPa and 43<64%). The results of this research seem to confirm the importance of this parameter in the studies of liquefaction of fully saturated sandy soils.