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Plane strain creep rupture of a saturated undisturbed clay Mallawaratchie, Dayalal Pandula

Abstract

Undrained constant stress level creep rupture tests have been performed on an undisturbed, normally consolidated under K₀ conditions, sensitive clay in a rectangular (1" x 4" x 2¼" high) plane strain apparatus. The behaviour resulting from total stress paths of increasing δ₁ (keeping δ₃ constant) and decreasing δ₃ (keeping δ₁ constant) was compared. Several undrained creep tests have also been performed in which triaxial specimens were first normally consolidated under K₀ conditions and then loaded by increasing δ₁, as well as decreasing δ₃. The plane strain and triaxial creep rupture test results were compared along with those reported by Snead (1970) . Snead tested the same clay but initially normally consolidated under isotropic stress and axially loaded in the conventional triaxial apparatus. The comparison of creep results under plane strain conditions shows that although the line of minimum strain rate versus time and the axial strain at minimum strain rate are essentially the same for increasing δ₁ and decreasing δ₃ stress paths, the deviator stresses (δ₁ - δ₃) versus minimum strain rates are different. The comparison of test results shows that the discrepancies in the creep rupture behaviour under plane strain and triaxial condition are slight, so long as the clay is initially K₀ consolidated. However, large discrepancies are seen if the triaxial samples are isotropically consolidated. In addition, all of the test data were compared along the lines of available methods for the prediction of slope failure. Of particular interest was the observation that both increasing δ₁ and decreasing δ₃ plane strain give the same prediction of time to slope failure. However the plane strain tests predict much shorter times to failure than do the isotropically consolidated triaxial tests.

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