When subjected to undrained cyclic loading, cohesionless soils are kno
wn to build up pore-water pressure to the extent that the soil loses t
he effective confining pressure completely, leading to what is known i
ts liquefaction. Presented in this paper is an elastoplastic model tha
t is capable of describing the stress-strain behavior of sands during
such an event. The model is developed by modifying an earlier model, w
hich was shown to be capable of modeling the behavior of sands during
monotonic loading. Two procedures, one employing an associated flow ru
le and another employing a nonassociated flow rule, are proposed for m
odeling the pore pressure and strain responses during stress reversal,
and their potential for modeling liquefaction behavior is explored. T
he model's capability is examined by comparing the theoretical predict
ions with experimental triaxial responses.