Stress-dependent behavior of saturated clay

Abstract

A program of K[subscript 0]-consolidated undrained triaxial compression tests has been performed to investigate the effects of consolidation stress level on the compression and shear behavior of resedimented Boston blue clay (RBBC). Specimens were consolidated to maximum vertical effective stresses in the range 0.15–10 MPa and tested at three overconsolidation ratios (OCR): 1, 2, and 4. The results show that the virgin compression curves are essentially linear in e–log σ[' over v] space over the consolidation stress range. However, the normally consolidated K[subscript 0] stress ratio increases with the level of consolidation stress. The stress–strain–strength properties measured in undrained shear are significantly affected by the consolidation stress level at each OCR and show indications of non-normalizable behavior. At high pressures, the undrained shear stress–strain behavior becomes more ductile, requiring larger strains to mobilize peak resistance and exhibiting less post-peak strain-softening. The undrained strength ratio (s[subscript u]/σ[' over vc]) is not uniquely controlled by OCR as suggested by the SHANSEP equation, but consistently decreases with increasing consolidation effective stress. There is notable reduction in the stiffness ratio (E[subscript u]/σ[' over vc]) with stress level, and significant decrease in the large-strain friction angle.