Time-Dependent Triaxial Relaxation Behavior of a Resedimented Clay

The paper describes the results of K0 consolidated-undrained triaxial compression relaxation tests on resedimented Boston Blue Clay (BBC) using a computer-automated triaxial apparatus. Specimens were either normally consolidated (overconsolidation ratio, OCR = 1) or had an OCR = 4, and they were sheared at different axial strain rates to axial strains (ea) from 0.1 to 15%. Each strain level was maintained until the monitored shear stress and pore pressure reached equilibrium levels. The results show that a single specimen can be used reliably for multiple relaxation tests. During relaxation, the rate of normalized shear stress decay with log time, (-?q/s´vm)/?logt, is approximately constant, regardless of ea or OCR. Changes in shear-induced pore pressure during relaxation were negligible except when specimens were rapidly sheared. Independent of OCR, end-of-relaxation equilibrium stress states for relaxation strains ea = 1.5% lie on a line of obliquity defined by K = s´h/s´v = 0.50, compared to K0 = 0.49 for OCR = 1 BBC; whereas, for ea = 2.5%, the equilibrium states lie on a steeper obliquity line defined by K = 0.40.

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