General stress-strain, modulus degradation, and directional stiffness dependence responses of compressible Chicago glacial clays are examined through a series of drained directional stress probes in a triaxial cell. Shear and volumetric stress-strain behaviors of specimens cut from block samples vary strongly as a function of stress probe direction. Limit points were determined for each stress probe and indicate that a closed limit state surface may be drawn around the experimental data. Modulus degradation behaviors, in terms of apparent secant shear modulus Gsec and apparent secant bulk modulus Ksec, demonstrate that these soil moduli are directionally dependent at all strain levels, including at strains as low as 0.001%. Unloading moduli, defined as a reduction of either shear or mean normal stresses, were observed to be significantly greater than loading moduli. These strain-level and directionally dependent responses imply that these freshwater clays are incrementally nonlinear. Copyright ASCE 2006.