ISSN: 1945-7545
CODEN: GTJODJ
Page Count: 9

Time-Dependent Triaxial Relaxation Behavior of a Resedimented Clay

Sheahan, TC
Assistant professor, Northeastern University, Boston, MA

Ladd, CC
Professor, Massachusetts Institute of Technology, Cambridge, MA

Germaine, JT
Principal research associate, Massachusetts Institute of Technology, Cambridge, MA

Abstract

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 (ε_a) 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, (−Δq/σ′_vm)/Δlogt, is approximately constant, regardless of ε_a 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 ε_a ≤ 1.5% lie on a line of obliquity defined by K = σ′_h/σ′_v = 0.50, compared to K₀ = 0.49 for OCR = 1 BBC; whereas, for ε_a ≥ 2.5%, the equilibrium states lie on a steeper obliquity line defined by K = 0.40.

Keywords:
automation, clays, consolidated-undrained tests, K0 consolidation, rate effects, relaxation, rheology, time effects, triaxial test

Paper ID: GTJ10305J
DOI: 10.1520/GTJ10305J
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