Mode I and mixed mode fracture mechanics testing of WIPP salt

The Waste Isolation Pilot Plant (WIPP) is an underground transuranic nuclear waste repository located in bedded salt formations in southeastern New Mexico. Excavation of rooms and shafts at the WIPP will induce deviatoric stresses in the surrounding rock, resulting in inward creep deformation and perhaps in the production of a disturbed rock zone (DRZ) characterized by microfractures. The stress conditions required for crack propagation are described by the material fracture toughness. Mode I (tensile) and mode II (shear) fracture toughness values were obtained for WIPP salt using the single edge cracked half disc specimen (or semicircular bend specimen) in three-point loading. The experimental method and test results are given in this paper. There are many assumptions inherent in applying fracture mechanics techniques to WIPP salt, and these assumptions should be considered in application of the data.