EVALUATION OF TIME-DEPENDENT DEFORMATION PROPERTIES
OF SEDIMENTARY SOFT ROCK AND THEIR CONSTITUTIVE MODELING
KIMITOSHI HAYANO,
MASASHI MATSUMOTO ,
FUMIO TATSUOKA and JUNICHI
KOSEKI
ABSTRACT A triaxial testing system with local axial strain
measurements was developed to accurately evaluate the time-dependent
deformation properties of sedimentary soft rock. A series of
consolidated triaxial creep tests were conducted on undisturbed samples
of sedimentary silt-sandstone and mudstone. Drained creep tests, each
lasting for three days, were performed at several deviator stresses in
the course of drained triaxial compression. Creep axial strains measured
locally at the lateral surface of the specimen were always noticeably
smaller than externally measured ones, indicating significant
time-dependent effects of bedding error occurring at the specimen ends.
In these triaxial tests, the axial strain rate was stepwise changed
during monotonic shearing to evaluate the effects of strain rate and its
change on the stress-strain behaviour. It is shown that instantaneous
irreversible strain and its rate uniquely control the current stress
state whether the strain rate is constant or continuously changing. This
isotach property is modeled in a simple model to be applied to the
limited test condition examined. It is shown that this model can predict
adequately the measured stress-strain-time behaviour for various time
histories of strain (or stress).
Key words: creep, (local strain measurement), soft
rock, strain rate, stress-strain relation, time-effect,
triaxial test (IGC: F6)
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