||Modelling of Rock Salt Creep
||Agergaard, Frederik Ancker (Arctic Technology Centre, Department of Civil Engineering, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
||Hededal, Ole (Section for Geotechnics, Department of Civil Engineering, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
Christensen, Helle Foged (GEOLAB, Danish Geotechnical Institute)
||Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark
||Rock salt deformation behaviour are often said to correspond to that of a very
viscosity fluid, hence a rheologic material model could be a good tool for describing
the stress-strain relations. This thesis treats the application of a rheologic
model introduced by Cristescu  as the tool for modelling rock salt
The basis of such a model is a well defined failure and volumetric behavior. It
is shown how the various functions making up the constitutive equation are
determined from experimental data and which assumptions must be made
for it to be fully functional. The model in question treats the transient and
steady-state creep contributions as an additive term, thus allowing for particular
determination and modelling.
An attempt to implement the model into a numeric MATLAB script has been
conducted, however not fully succesful as the strict determination of the irreversible
stress work, an internal state variable serving as a work-hardening
parameter, failed due to inadequate knowledge of the the total stress-strain
Uniaxial creep tests have been performed on rock salt from the Tostrup 5 well
and steady-state creep behaviour were observed after approximately 20 days.
An unexpectedly strong variation of the relative humidity during the tests,
complicated the outcome of the tests as well as the single loadstep introduce
were insufficient for use in calibration of the constitutive model.
It is suggested that a test setup providing data material for full calibration
of the investigated model should comprise 4-6 triaxial tests run to failure at
various stress rates and mean stress, and an equal number of triaxial stepwise
creep tests, if continued long enough, providing a sound basis for determination
of both transient and steady state creep contributions.
||Technical University of Denmark (DTU) : Kgs. Lyngby, Denmark
Creation date: 2010-02-23
Update date: 2010-02-23