Special Problems in Making Geotechnical Measurements in Salt

The transfer of experience, theory, and instrumentation suitable for hard rock media has posed numerous problems which this paper will address. Foremost of these pertains to the time-dependent (creep) behavior of salt. The theoretical mechanism is elusive; creep laws formulated to predict this behavior represent the state of the art in regression analysis. Furthermore, long term experiments (1 year) that would be necessary to determine creep mechanism(s) are enormously expensive and tie-up test equipment. Second, tests for determining in situ stress are based on the theory of elasticity. However anelastic (non-recoverable) strains contribute a significant portion of the material behavior precluding back calculating in situ stresses. Another problem pertains to the rate-dependent behavior of salt. Loading and temperature gradients experienced in the laboratory are more severe than would be experienced in a repository. Significant differences in material behavior can be expected along with special problems with instrumentation.