Experimental determination of rock joint stiffness for 'healed joints' in welded tuff

Fourteen uniaxial joint compression and five direct shear tests were run to determine the joint normal and shear stiffnesses on specimens with type 1 fracture joints (healed joints filled with vapor-phase mineral deposits) obtained from the Yucca Mountain site. The uniaxial joint compression results show that these joints behave linearly up to over 85% of their loading history. They are stiff with strengths very close to the strength of the intact rock. Results obtained from the direct shear testing show that the normal stiffness increases with increasing normal stress. Shearing through asperities gives high joint shear stiffness values, which reduce gradually as the contact surfaces smoothen out.; Intact rock Young's moduli and intact rock normal stiffness obtained from the uniaxial joint compressive tests ranged from 29.42 to 68.68 GPa and 9.19 to 24.79 GPa/mm respectively. The ranges for Young's moduli and normal stiffness for rock section with the joint are from 14.75 to 35.75 GPa and 4.61 to 11.17 GPa/mm respectively. Joint normal stiffness and joint shear stiffness ranged from 7.16 to 179.68 GPa/mm and 3.09 to 78.81 GPa/mm respectively.