A three-dimensional elastic-plastic isotropic work-hardening constitutive relationship has been developed for simulating the stress-strain-pore pressure response of fluid saturated sand. The model reproduces the hysteretic behavior of the material under hydrostatic and deviatoric states of stress accounting for shear-induced volume change and the effect of superimposed hydrostatic stress on the shearing response. The behavior of the constitutive model under axisymmetric triaxial test conditions is examined and correlated with experimental results for a fluid saturated sand at both loose and dense initial states of compaction.