The effect of volumetric strain on elastic parameters for rock salt

An experimental program aimed at characterizing the elastic response of roc k salt under both quasi-static and dynamic conditions has been performed. T he program includes uniaxial short-term tests and uniaxial creep tests. Dur ing axial loading, the travel times of longitudinal and transverse elastic waves propagating in the specimen were simultaneously recorded, together wi th the strain state. The test results show that in uniaxial, short-term tes ts, the dynamically determined elastic parameters vary in a similar way as does the irreversible volumetric strain, i.e. they increase in the compress ibility domain, are nearly constant in the transition zone from compressibi lity to dilatancy, and decrease in the dilatancy domain. In creep tests, th e variation is more complicated: the elastic parameters vary immediately af ter 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 e lastic/ viscoplastic constitutive equation that describes compressibility a nd/or dilatancy and damage (as the total energy released by microcracking d uring dilatancy) were determined. Copyright (C) 2000 John Wiley & Sons, Ltd .