Stress-strain-strength responses of compressible chicago glacial clays

The stress-strain-srength responses of compressible Chicago glacial clays are presented.These clays are lightly overconsolidated supra- or subglacial tills. Fixed piston and Shelby tube samples from various locations in the Chicago area were subjected to an extensive laboratory testing program, including index property, consolidation, direct shear, and K₀-consolidated, and undrained triaxial compression and extension tests. Results of the experimental program indicated the strengths of tills can be normalized when proper consideration is given to variations in natural water content. The different undrained strengths in compression and extension indicate that the clays exhibit stress-induced anisotropy. Initial undrained elastic moduli of the clays vary systematically with the overconsolidation ratio. Comparisons are made between strengths computed from relations based on normalized undrained strengths determined in the laboratory and those based on in-situ tests made at several locations. These data suggest that field vane strengths represent a conservative index of undrained shear strength for these Chicago clays.