CK0UC Shear Strength of Normally Consolidated Clays from CIUC Tests

Because of their practicality and simplicity, consolidated isotropic undrained compression (CIUC) triaxial tests are commonly used in practice to determine the undrained shear strength of cohesive soils, even though CAUC or CK0UC tests would model in situ conditions more effectively. As a consequence, engineers must implicitly assume that the undrained shear strength and strength ratio τf/σc′ obtained from CIUC tests is representative of the in situ or K0 strength. The paper describes a simple procedure based on critical state soil mechanics principles, Skempton's pore pressure equation, and Jaky's K0 relationship, to enable the prediction of in situ or K0 undrained shear strength of normally consolidated clays directly from the results of a single CIUC test. Based on limited available test data in which both types of tests were conducted on the same soil, the procedure is shown to be valid and sufficiently accurate for practical purposes.