Laboratory study on the liquefaction resistance of sand-silt mixtures: effect of grading characteristics

The liquefaction susceptibility of saturated medium sand-silt mixture samples is evaluated by monotonic and cyclic undrained triaxial laboratory tests that were carried out on reconstituted specimens at various relative densities (D(r) = 20, 53 and 91%) and a constant confining pressure (sigma'(3) = 100 kPa). The test results were used to conclude on the effect of grading characteristics and other parameters on the liquefaction resistance of the sand-silt mixtures. The monotonic test results indicate that the undrained shear strength at the peak and the undrained residual strength can be correlated to the coefficient of uniformity (C(u)) and the average diameter (D(50)). Indeed, they decrease linearly with the increase of the uniformity coefficient and decrease of the average diameter. It is found that a relationship between the liquefaction resistance and any of the diameters (D(10) or D(50)) and the coefficient of uniformity (C(u)) would be more realistic than to build a relation between the coefficient of gradation (C(c)) and the liquefaction resistance. Undrained cyclic triaxial tests indicate that the cyclic liquefaction resistance of the sand-silt mixtures decreases linearly with the decrease of the effective diameter (D(10)) and mean size (D(50)) and increase of the fines content for the fines content range tested (Fc = 0-40%).