CREEP-INDUCED CLEAVAGE FRACTURE IN WIPP SALT UNDER INDIRECT TENSION

The phenomenon of cleavage fracture initiation in rock salt undergoing concurrent creep was studied experimentally using the Brazilian indir ect tension test technique. The tensile creep and cleavage fracture be haviors were characterized for rack salt from the Waste Isolation Pilo t Plant (WIPP) site. The Brazilian test consists of a compressive line load applied diametrically on a disk specimen to produce a region of tensile stress in the center of the disk. The damage processes were do cumented using video photography. The experimental results were analyz ed in terms of a wing-crack feature model and an independently develop ed, coupled time-dependent, mechanism-based constitutive model whose p arameters were obtained from triaxial compression creep tests. Analyti cal results indicate that coupling between creep and cleavage fracture in WIPP salt results in a fracture behavior that exhibits time-depend ent characteristics and obeys a failure criterion involving a combinat ion of stress difference and tensile stress. Implications of creep-ind uced cleavage fracture to the integrity of WIPP structures are discuss ed.