A comparison of Unified creep-plasticity and conventional creep models for rock salt based on predictions of creep behavior measured in several in situ and bench-scale experiments

A unified creep-plasticity (UCP) model, a conventional elastic-secondary creep (ESC) model, and an elastic-secondary creep model with greatly reduced elastic moduli (RESC model) are used to compute creep responses for five experimental configurations in which rock salt is subjected to several different complex loadings. The UCP model is exercised with three sets of model parameters. Two sets are for salt from the site of the Waste Isolation Pilot Plant (WIPP) in southeastern New Mexico, and the third is for salt from Avery Island, Louisiana. The WIPP reference secondary creep parameters are used in both the EC and RESC models. The WIPP reference values for the elastic moduli are also used in the ESC model. These moduli are divided by 12.5 in the RESC model. The geometrical configurations include the South Drift at the WIPP site, a hypothetical shaft in rock salt, a large hollow cylinder of rock salt subjected to external pressure while still in the floor of a drift at Avery Island, Louisiana, a laboratory-scale hollow cylinder subjected to external pressure, and a model pillar of salt subjected to axial load. Measured creep responses are available for all of these experiments except the hypothetical shaft. In all cases, deformationsmore » computed with the UCP model are much larger than the ESC predictions and are in better agreement with the data. The RESC model also produces larger deformations than the ESC model, and for the South Drift, the RESC predictions agree well with measured closures. 46 refs., 19 figs., 2 tabs.« less