Publications

A series of cyclic, direct-shear tests was conducted on several replicas of a tensile fracture of welded tuff to verify the graphical method proposed by Saeb (1989) and by Amedei and Saeb (1990). Tests were performed under different levels of constant normal load and constant normal stiffness. Each test consisted of five cycles of forward and reverse shear. The effect of cyclic loading on the fracture shear behavior was investigated. Fracture surface asperity degradation was quantified by comparing fracture fractal dimensions before and after shear.

Licensing of the potential nuclear-waste repository at Yucca Mountain by the Nuclear Regulatory Commission would require, among other things, demonstrations of the long term usability of the underground facilities. Such a demonstration involves analysis of the mechanical response of the rock to the presence of underground openings and heat-producing waste, which in turn requires data on the mechanical properties of the rock. This document describes the experimental results from a scoping study which led to the development of procedures for performing quality-affecting rock-mechanics experiments on intact rock. The future experiments performed with these procedures will produce information on the time-dependent deformation of welded tuff and represent one aspect of the overall effort to characterize the rheology of the rock mass. 3 refs., 42 figs., 6 tabs.

Three series of measurements were performed on oriented cores of several Yucca Mountain tuffs to determine the importance of mechanical anisotropy in the intact rock. Outcrop and drillhole samples were tested for acoustic velocities, linear compressibilities, and strengths in different orientations. The present data sets are preliminary, but suggest the tuffs are transversely anisotropic for these mechanical properties. The planar fabric that produces the anisotropy is believed to be predominantly the result of the preferred orientation of shards and pumice fragments. The potential of significant anisotropy has direct relevance to the formulation of constitutive formulation and the analyses of an underground opening within Yucca Mountain.