UNIAXIAL STRENGTH TESTING OF NONWELDED CALICO-HILLS TUFF, YUCCA-MOUNTAIN, NEVADA

A detailed investigation of the strength properties of Calico Hills tu ff was undertaken to further characterize the behavior of this unit. U niaxial compression tests on 43 specimens of massive and reworked tuff show a dependence of peak strength and Young's modulus on the total p orosity, and thereby on the geologic history of the Calico Hills tuff. The average Young's modulus, Poisson's ratio, and compressive (peak) strength of dry specimens of massive (and reworked) tuff are: 5.43+/-0 .96 GPa (9.80+/-0.89 GPa), 0.194+/-0.052 (0.244+/-0.067), and 26.34+/- 5.13 MPa (38.64+/-4.96 MPa). Wet specimens of massive tuff have compre ssive strengths of 15.34+/-0.70 MPa, lower than those of dry specimens . The post-peak region for this brittle tuff is characterized by rapid load drops and well-defined residual strengths associated with growth of macrocracks and small faults in the specimens.