The peak undrained resistance (σd,upeak) of a loose sand during liquefaction under monotonic loading does not necessarily occur on or near the Mohr Coulomb failure envelope. Instead, it occurs as that combination or product of a decreasing effective confining pressure (
) and an increasing stress level (SL). The condition in which this product is a maximum occurs at a particular point on a plot of the deviator stress (σ
d
) versus volumetric strain (ε
v
) as assessed from a drained triaxial test. A method is presented whereby a single drained test with volume change measurement can be used to assess this undrained peak. This is a refinement of a more complete effective stress method of liquefaction analysis that requires only drained triaxial testing.
