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 ( 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%).