Fourteen uniaxial joint compression tests were run to determine the normal and shear stiffnesses of 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. Five direct shear tests were run on open, separated, joints. 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 smooth. Intact rock Young's moduli obtained from the uniaxial joint compressive tests average 40.6 GPa, and range from 29.42 to 68.68 GPa. The Poisson's ratio averages 0.21, and ranges from 0.12 to 0.5. Joint normal stiffness (average 26 GPa/mm) and joint shear stiffness (average 10.82 GPa/mm) of the healed joints, i.e. joints filled with vapor-altered minerals, range from 7.16 to 64.77 GPa/mm and 3.09 to 28.41 GPa/mm respectively. From the stiffness of the healed joint, we have calculated the Young's modulus of the vapor phase altered joint infilling. The Young's modulus of the vapor-altered joint filling material averages 8.29 GPa and ranges from 2.15 to 19.43 GPa. Given the pervasive presence of such altered rock, usually in the form of sub-spheroidal three-dimensional pockets, this property should be of value for any numerical modeling attempting to describe the mechanical behavior of these tuff formations at the level of detail where inclusions might be a factor. Recommendations are given for the pursuit of further investigations of the mechanical properties of joints. In order to assure maximum usefulness of the results, it would be desirable to assure that samples can be obtained from those joint systems most likely to affect repository performance.
Joints (Geology); Nevada – Yucca Mountain; Rock mechanics; Rocks – Fatigue; Rocks – Testing; Strains and stresses; Volcanic ash; tuff; etc.
Earth Sciences | Geology | Geophysics and Seismology | Tectonics and Structure
Daemen, J. J.,
Smiecinski, A. J.
Experimental determination of stiffness of joints in welded Tuff.
Available at: http://digitalscholarship.unlv.edu/yucca_mtn_pubs/76