Current practice (2009) for seismic analysis of embankment dams relies heavily on empirical correlations with penetration resistance (standard penetration test or cone penetration test) to predict the residual undrained shear strength of liquefied foundation materials. At least six such relationships have been published for the SPT alone, in different “formats.” Some apply a fines adjustment to the SPT blowcounts, but others do not; some express the predicted strength as a ratio with pre-earthquake effective overburden stress, whereas others predict it directly, without explicit consideration of overburden. For the foundations of embankment dams, the difference between the strength-ratio approach and prediction of Sur directly, from the SPT alone, can be important. In this paper, the underlying assumptions and data are reviewed critically, including the effects of different material types and different mechanisms governing the strength. Simplified statistical analyses were applied in attempt to determine the most appropriate format for a correlation and to obtain a new correlation that explicitly accounts for both overburden and blowcount
