Two analytical models for evaluating piezocone penetration tests (CPTU) in offshore clays are applied to obtain values of effective stress friction angle, rigidity index (I/sub R/), undrained shear strength (s/sub u/) and yield stress ratio (YSR) with depth. The solution requires the values of effective friction angle defined at both maximum deviator stress (/spl phi//sub 1/') and maximum obliquity (/spl phi//sub 2/') which associate with total cone resistance (q/s/sub u/b t/) and porewater pressure (u/sub 2/), respectively. A hybrid analytical model based on spherical cavity expansion - critical state soil mechanics (SCE-CSSM) provides the magnitudes of YSR, I/sub R/, and s/sub u/, while an effective stress plasticity solution developed at NTNU obtains /spl phi//sub 1/' and /spl phi//sub 2/'. Using data from the upper Unit I plastic clay at Troll field for illustration, the interpreted CPTU results compare favorably with independent reference values obtained from laboratory triaxial compression and consolidation tests.
Paul W. Mayne, Shehab S. Agaiby and Zhongkun Ouyang
Keywords: clay, cone penetration, stress, friction angle, piezocone, preconsolidation, strength, yield stress
Publisher: DFI