Confining stress and static shear effects in cyclic liquefaction

Liquefaction resistance of a sand under cyclic loading is assessed and the effects of the levels of confining pressure and static shear on resistance to liquefaction are investigated. Site-specific values of the resistance under specified levels of confining and static shear stresses are measured in the laboratory. The measured values are compared with those which would be predicted by the application of empirical multiplying factors K-sigma and K-alpha to the reference resistance at 100 kPa effective confining stress with no static shear. It is shown that K-sigma and K-alpha are not independent, as assumed in current practice. The combined factor K-sigma x K-alpha resulting from the empirical method is shown to underestimate the cyclic resistance ratio regardless of the initial density and confining and static shear levels. The degree of conservatism is most dramatic at looser density states.