Constitutive behavior of reconsolidating crushed salt

Abstract

The constitutive model used to describe deformation of crushed salt is presented in this paper.Two mechanisms -dislocation creep and grain boundary diffusional pressure solutioning -are combined to form the basis for the constitutive model governing deformation of crushed salt. The constitutive model is generalized to represent three-dimensional states of stress. Recently completed creep consolidation tests are combined with an existing database that includes hydrostatic consolidation and shear consolidation tests conducted on Waste Isolation Pilot Plant (WIPP) and southeastern New Mexico salt to determine material parameters for the constitutive model. Nonlinear least-squares model fitting to data from shear consolidation tests and a combination of shear and hydrostatic tests produces two sets of material parameter values for the model. Changes in material parameter values from test group to test group indicate the empirical nature of the model but show significant improvement over earlier work. To demonstrate the ' predictive capability of the model, each parameter value set was used to predict each of the tests in the database. Based on fitting statistics and ability of the model to predict test data, the model appears to capture the creep consolidation behavior of crushed salt quite well..

Laboratory Characterization of Mechanical and Permeability Properties of Dynamically Compacted Crushed Salt

“…A suite of shear consolidation creep test results were added to a database of similar results for the purpose of estimating parameters in a constitutive model that represents the behavior of crushed salt (Callahan et al, 1998a). The current testing was performed at higher initial fractional densities (0.9) and stresses (1 to 5 MPa) than were used in previous programs to give better coverage of the range of conditions likely to be encountered during sealing operations at the WIPP.…”

“…Further, a minor amount of added moisture greatly enhances densification (Spiers and Brzesowsky, 1993). Consideration of the fundamental defonnational processes guided formulation of the constitutive model for reconsolidating crushed salt (Callahan et al, 1998a). As crushed salt is loaded, the principal densification mechanism of fluid-phase grain boundary solutionhedeposition is rampant.…”

“…The laboratory results were expected to (1) illuminate the phenomenology of crushed-salt deformation behavior and (2) add test results to a small preexisting database for purposes of estimating parameters in a crushed-salt constitutive model. The candidate constitutive model for dynamically compacted crushed salt (Callahan et al, 1998b) was refined in parallel with this laboratory testing and the current model refinements have been published (Callahan et al, 1998a). The work was conducted under RE/SPEC's QA Program as specified in the document, "Quality Assurance Project Plan: Rock Mechanics Analysis Support for Sandia National Laboratories, AG-4911 @SI Job 325), RSI QAPP-09.…”

Crushed Salt Constitutive Model

“…Since the status of the crushed-salt constitutive model was reported by Callahan et al [1998b] and , five additional laboratory tests have been completed and are included in the present work. Two of these tests are shear consolidation tests; three of the tests are constant strain-rate tests.…”

Petrophysical and Capillary Properties of Compacted Salt

“…Compaction of backfilled salt will continue until mechanical and geochemical equilibrium is reached. Various constitutive models have been reported to describe the mechanical behaviour of compacting crushed salt under different conditions (Zeuch and Holcomb, 1984;Case et al, 1987;Spiers et al, 1988;Zeuch, 1990;Hein, 1991;Brodsky et al, 1995Brodsky et al, , 1996Chumbe et al, 1996;Davidson and Dusseault, 1996;Callahan et al, 1998;Olivella and Gens, 2002).…”