ABSTRACT: Rock salt exhibits a strain and time dependent response under deviatoric stresses. The practical implications of this creeping behavior have been studied extensively for the design of underground excavations. Advanced constitutive models combined with modern computing capabilities can be used for the analysis of rock salt behavior under complex stress regimes. The implementation and application of state of the art constitutive models to practical situations, such as those encountered in conventional underground mining, is progressively emerging. The following presents an investigation on the application of a strain hardening model to represent unified transient and steady state creep at the Morton Salt Weeks Island mine (Louisiana). A twodimensional modelling simulation is presented to illustrate how traditional convergence measurements at the mine can be used to capture the effect of panel sequencing on creep behavior, and how to introduce the effect of the transient phase on the long term steady state behavior.

1. INTRODUCTION

Polycrystalline halite, the mineral of rock salt, presents unique mechanical features from the response to natural stress fields and around man-made excavations. Rock sallt exhibits a deviatoric stress induced response, commonly referred to as creep, which results in inelastic deformation under sustained loading. Various investigations have indicated that rock salt exhibits a ductile behavior below its brittle (damage initiation) threshold which results in inelastic deformation (without failure).

The ductile behavior of rock salt is particularly important when considering long term conditions around underground excavations. Numerous studies has been devoted to better understand this long term behavior and overall integrity of underground salt caverns (e.g. Vouille et al., 1993; Souley et al., 2008; Bérest et al, 2013; Warren, 2017). Salt caverns (and other openings in rock salt) have generated an interest regarding oil and gas storage and the long term disposal of radioactive waste due to the very low permeability of halite and its intrinsic healing capabilities (Bérest et al., 1996; Du et al., 2012; Moghadam et al, 2013). For instance, the waste isolation pilot plant (WIPP), located in New Mexico, USA, has generated extensive research results that have led to the development of advanced constitutive modelling concepts (e.g. Munson and Dawson, 1979; Munson, 1997), and sampling and characterization techniques (Brush, 1990).

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