The influence of pore pressure and porosity on the ductile deformation of granular salt was experimentally investigated under hydrostatic compression. Confining and pore pressures were independently controlled while granular salt samples exhibited rate-dependent deformation that resulted in large decreases of sample volume and porosity. The sample deformation rates were observed to correspond with both the sample porosity and the pressure difference between the confining and pore pressures. Post-test observations revealed that the reduced porosity was caused by the solid particles deforming in a ductile manner. Insight into the cause of ductile deformation was gained by considering the local stress distribution within a sample, which was approximated with the use of a representative volume element (RVE). Analysis of the local stress distribution with the use of an RVE showed how the magnitude of local shear stress depends on both porosity and pressure difference, which is consistent with the experimental results.
A continuum based constitutive model was developed at the particle scale to predict the bulk volumetric deformation of granular salt under hydrostatic compression. The constitutive model consists of a RVE having the geometry of a thick-walled sphere and a set of constitutive equations that govern the solid-phase deformation. The constitutive model is able to capture the coupled influence of pore pressure and porosity on the ductile deformation of solid particles that results in bulk volume reduction. Numerical results were obtained with the finite element method, and these results were in good agreement with experimental data.
granular salt, effective stress, hydrostatic compression, localized stress, inelastic deformation, constitutive model
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Lampe, Brandon C.. "Experimental Investigation of and Constitutive Model for the Thermo-Poro-Mechanical Deformation of Granular Salt Under Hydrostatic Compression." (2018). https://digitalrepository.unm.edu/ce_etds/206