ISSN: 0149-6115
Page Count: 9

Time-Dependent Triaxial Relaxation Behavior of a Resedimented Clay

Sheahan, TC
Assistant professor,Northeastern University,MA,

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

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