Small strain behavior of compressible Chicago glacial clay

The evaluation of ground deformations under service or construction loading is frequently the most critical element to the successful design and construction of any geotechnical project, especially those in urban environments. The recognition that soil moduli are strain level and directionally dependent allows for significant improvement in the predictive capabilities of ground deformations using numerical modeling methods. This dissertation presents the results and analysis of a comprehensive laboratory investigation of the very small and small strain behavior of compressible, lightly overconsolidated Chicago glacial clays using hand-cut block samples of Chicago clay and a custom-designed triaxial testing system.; General stress-strain, modulus degradation, and directional stiffness dependence responses of nominally identical, K0 consolidated block specimens were examined through a series of drained directional stress probes in 10 different directions. Shear and volumetric stress-strain behavior was seen to vary strongly as a function of stress probe direction. The 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 behavior, in terms of secant shear modulus Gsec and secant bulk modulus Ksec, demonstrates conclusively that the soil moduli are directionally dependent at all strain levels, including at strains as low as 0.001%. Unloading moduli were observed to be significantly greater than loading moduli. The maximum soil stiffness tends to occur for stress path directions rotated 180 to 230 degrees from the previous stress history. This behavior is confirmed through the use of strain response envelopes, which allow general constitutive responses to be examined for axisymmetric stress states. These strain-level and directionally dependent responses lead to the conclusion that these compressible Chicago glacial clays are incrementally nonlinear.; Bender element tests were conducted during K0 consolidation and directional stress probes. The mean normal effective stress p ' was seen to be the controlling factor for GBE during both consolidation and stress probing. Bender element tests can be employed to estimate the residual effective stress after sampling pr', which may be used as a qualitative indicator of sample disturbance. The correct interpretation of bender element tests requires that the dispersive nature of propagating waves in a triaxial specimen be considered.