An insight into the liquefaction resistance of sand using cyclic undrained triaxial tests: Effect of the relative density and the loading amplitude

Abstract A stability analysis of soils prone to liquefaction based on their undrained shear-strength characteristics is an indispensable challenge in earthquake geotechnical engineering. This paper presents a laboratory study of the influence of relative density on the cyclic behavior of Chlef sand. The experimental program includes undrained, triaxial cyclic tests that were carried out for three different relative densities (Dr = 15, 50 and to 65 %) with various cyclic stress ratios (CSR = 0.15, 0.25 and 0.35). All the samples were consolidated under one initial effective confining pressure σ'c = 100 kPa. The main results show that the increases in the relative density led to significant increases in the shear strength established by an increase in the number of cycles and with an exponential rise. In contrast, it was demonstrated that the number of cycles was decreased when increasing the cyclic stress ratio due to the shearing frequency. The two main effects of the studied parameters did not have the same influence on the cyclic undrained response of the sandy soil submitted to seismic loading: an increase of the deviatoric stress due to the high relative density that participates in the increase of the loading capacity of the compacted soils by minimizing the void ratios, and an increase of the pore-water pressure that has a negative effect on the liquefaction of the soil. From the results obtained, it can be concluded that these two mechanisms led to a global increase of the maximum shearing stress.