Mechanical properties of tuffaceous rocks under triaxial conditions

Nicholas William Hudyma, University of Nevada, Las Vegas


Yucca Mountain has been designated as a potential site for a high level nuclear waste repository. Part of the site characterization program is an investigation of the mechanical properties of the tuffs which comprise Yucca Mountain. The study tested specimens of TCw tuff in triaxial compression to observe the effects of confining pressure, saturation, strain rate, and anisotropy on the compressive strengths and Young's Moduli of the specimens. Test results have shown that increasing the confining pressure increased the compressive strength and generally increased the Young's Modulus. Saturation appears to lower both the compressive strength and Young's Modulus of the specimens. Increasing strain rates increase the compressive strengths, but lowers the Young's Modulus values. There appears to be a stiffness anisotropy where the specimens are stiffer perpendicular to the orientation of the the lithophysal cavity orientation. Correlations with porosity have shown as increase in porosity generally lowers both the compressive strength and the Young's Modulus of the specimens. From the triaxial tests, the Mohr-Coulomb strength parameters have also been determined. A comparison between the strengths and modulus values from this study, values from previous studies and the suggested values reveal that the values computed for this study are generally lower than the previously published data. The dicrepancy may be due to sample and specimen differences between the studies.