The effect of volumetric strain on elastic parameters for rock salt

An experimental program aimed at characterizing the elastic response of rock salt under both quasi-static and dynamic conditions has been performed. The program includes uniaxial short-term tests and uniaxial creep tests. During axial loading, the travel times of longitudinal and transverse elastic waves propagating in the specimen were simultaneously recorded, together with the strain state. The test results show that in uniaxial, short-term tests, the dynamically determined elastic parameters vary in a similar way as does the irreversible volumetric strain, i.e. they increase in the compressibility domain, are nearly constant in the transition zone from compressibility to dilatancy, and decrease in the dilatancy domain. In creep tests, the variation is more complicated: the elastic parameters vary immediately after stress application, but continue to vary slowly in time when stress is kept constant. Moreover, both G and K increase with time when Et increases and vice versa (superscript I stands for 'irreversible' and subscript v for 'volumetric'). It appears that the elastic parameters depend on the strain history or, perhaps on some other type of damage parameters. Thus, the non-constant elastic parameters governing the 'instantaneous' response in an elastic/ viscoplastic constitutive equation that describes compressibility and/or dilatancy and damage (as the total energy released by microcracking during dilatancy) were determined. Copyright (C) 2000 John Wiley & Sons, Ltd.