Undrained Strength Interrelationships among CIUC, UU, and UC Tests

Abstract

Consolidated‐isotropically undrained, triaxial compression (CIUC), unconsolidated‐undrained, triaxial compression (UU), and unconfined compression (UC) test results were used to develop interrelationships for the undrained shear strengths (su) obtained from these test types. Stress path evaluations were used to provide a general framework for interpretation of these interrelationships. The results show that the normalized undrained strengths [su(UUorUC)/su(CIUC)] are dependent on the overconsolidation ratio (OCR) or undrained strength ratio (su/σ¯vo). Softer clays have lower normalized undrained strength, while harder clays, including fissured clays, result in higher normalized undrained strength. Suggested correlations for these normalized undrained strengths or undrained strength ratios, as well as the linear regression data and confidence intervals corresponding to one standard deviation, are presented in this paper and show a consistent data population. Direct comparison of su from UU and UC tests shows that the UU results are closer to the CIUC results than the UC results, which is consistent with general supposition.