In urban areas, an accurate evaluation of ground deformations from various construction activities requires one to properly consider both the probable ground strain level under expected working conditions and the recent stress history of the soil. For well-designed projects, the levels of ground strains typically are less than 0.5%, emphasizing the need to investigate soil behavior at small strains. This dissertation presents the results and analysis of a laboratory investigation of the very small, small and large strain behaviors of compressible, lightly overconsolidated Chicago glacial clays. Triaxial tests were performed with bender elements and local LVDTs on high quality block samples taken from an excavation in Evanston, IL. Results of two types of drained stress probe tests with different pre-shear stress paths, "post-K0" and "post-unloading" probes, are compared in terms of general stress-strain, modulus degradation, and directional stiffness dependence to investigate the effects of recent stress history. Stress probes also were performed on specimens of the same clay reconstituted in a slurry consolidometer. Results were presented in terms of Strain Response Envelopes (SRE) to illustrate the directional dependence. Based on comparisons of the stress-strain data and moulus degradation curves of the two types of stress probe tests, the effects of recent stress history were apparent not only in shear and volumetric responses, but also in the cross-coupling between the shear and volumetric responses. The significant variability of the shear, bulk and cross-coupling moduli with stress path direction and strain level shown in the SREs provide experimental evidence that the Chicago clays are incrementally nonlinear. Results of tests conducted with three sets of bender elements show that compressible Chicago glacial clay is a cross-anisotropic material. An empirical correlation was established based on the elastic shear stiffness from bender element tests, "GBE," during K0-reconsolidation. By comparing the empirical correlation with the measured GBE in the stress region during probing, the deviation of GBE from values computed by the empirical relation directly relates to the yielding characteristics of the clay. Also, the shear modulus based on the shear wave velocity in axial direction agrees well with the field measured shear wave velocity by seismic CPT tests and the modulus from shear stress unloading types of stress paths in triaxial tests. Results of reconstituted samples can be used to investigate the effective stress at failure conditions of compressible Chicago clays, but the overall softer stress-strain responses, bender element results and smaller yield surface of the reconstituted samples suggest that reconstituted specimen behavior does not represent that of high quality natural samples of compressible Chicago glacial clays.

Last modified

• 08/30/2018

Creator

• Wan Jei Cho

DOI

• https://doi.org/10.21985/N2GB1P

Subject

• Civil and Environmental Engineering

Keyword

• Chicago clay
• small strain stiffness
• recent stress history

Date created

• 2007-07-24

Resource type

• Dissertation

Rights statement

• In Copyright