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Title Modelling of Rock Salt Creep
Author Agergaard, Frederik Ancker (Arctic Technology Centre, Department of Civil Engineering, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
Supervisor 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)
Institution Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark
Thesis level Master's thesis
Year 2009
Abstract 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 [1993] as the tool for modelling rock salt creep. 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 relation. 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.
Imprint Technical University of Denmark (DTU) : Kgs. Lyngby, Denmark
Pages 81
Fulltext
Original PDF Agergaard_2009_Modelling_of_rock_salt_creep.pdf (4.93 MB)
Admin Creation date: 2010-02-23    Update date: 2010-02-23    Source: dtu    ID: 258661    Original MXD