Experimental investigation of mechanical properties of bedded salt rock

Because of salt cavern utilization for liquid, gas and solid waste storage, salt rock mechanical properties are needed for assessments of facility, stability and safety. Bedded salt deposits are widespread and used as much or more than diapiric salt bodies as storage facility hosts, but experimental data on the mechanical properties of bedded salt rock with impurities are far less common than data available on relatively pure diapiric salt rocks. Through laboratory uniaxial and triaxial compression experiments on rock salt (halite), interlayers (anhydrite) and bedded composite specimens (anhydrite–halite and mudstone–halite), differences in mechanical properties of the various lithologies are explored. In the composite specimens, the weakest or the most deformable component governs the behavior. Also, the properties of bedded composite lithology specimens tend to be in between the property ranges of the “pure” lithologies. The elastic modulus of the bedded salt rock increases from 5.3 to 24.1 GPa with an increase in the confining stress from 0 to 15 MPa, with some evidence of sample damage. The ductile transition for halite at the strain rates used is at about σ3∼10 MPa.With increasing σ3, the anhydrite–halite composite lithology deformation showed strain hardening and a strong trend to ductile behavior as the halite bands tended to dominate the behavior. Strain incompatibility effects exist along interfaces between creeping and non-creeping phases in anhydrite–halite composite lithologies. Mudstone–halite rocks tended to be extremely weak, compared with all other specimens.