Investigation of an empirical creep law for rock salt that uses reduced elastic moduli

Early attempts to predict the creep response of rock salt around underground rooms at the Waste Isolation Pilot Plant (WIPP) produced closure estimates that were one-third to one-fourth of values measured in situ (Morgan et. al., 1985). A subsequent study (Morgan, et al., 1986) of the WIPP reference elastic secondary creep model (Krieg, 1984) used to make these predictions revealed that room closures and even closure rates could be increased by reducing the elastic constants. This study also indicated that a vertical cylindrical shaft configuration could be substituted for more complicated and expensive rectangular room configurations in studying constitutive parameters for rock salt. Sjaardema and Krieg (1986) used these results to determine how much the WIPP reference value of Young's modulus E had to be reduced to increase the creep closure and closure rate of a hypothetical borehole in rock salt by factors of 3.5 to 4. They found that E had to be divided by 12.5 to produce the desired results. 12 refs., 5 figs.