Thermomechanical Damage Recovery Parameters for Rocksalt From the Waste Isolation Pilot Plant

ABSTRACT: Laboratory healing tests were conducted on specimens of intact WIPP salt that were predamaged by straining under constant strain-rate triaxial stress conditions at low confining pressure (0.5 MPa) and near room temperature (25°C). Introduction of dilatant damage caused specimen volumes to increase and ultrasonic compressional wave velocities and amplitudes to decrease. Specimens were then loaded hydrostatically to 15 MPa at temperatures up to 70°C. Under these conditions, damage was partially recovered and specimen volume and compressional wave characteristics approached the values of the undamaged state. From these data, time constants and an activation energy were determined for the damage recovery process. The results have significant implications for sealing systems because they demonstrate that the healing process is quite rapid compared to the creep closure process.