ABSTRACT
A brief review of the role of laboratory testing for characterization of host rocks for nuclear waste repositories is presented. Micro-and macro-scopic deformation mechanisms are discussed and constitutive laws being considered are reviewed. More information is available for rocksalt under expected repository conditions and, consequently, it receives more attention in our review. A brief comparison is made between the creep and constant strain-rate tests leading to a hypothesis that there may be systematic differences between steady-state conditions developed by the two test types. This difference is explained by considering specific power dissipated and work done on the sample. The hypothesis is tested against data for wet Westerly granite. In conclusion, progress has been made during the past five years but research and development should continue.
INTRODUCTION
From a general point of view, a nuclear waste repository can be viewed as a perturbation of existing thermal, mechanical, hydrological, and chemical systems of the site. At a well-chosen site, these systems will be near equilibrium before the beginning of repository development, i.e., the site will have low seismicity, low probability of volcanism, etc. A well-designed repository will presumably disturb the existing systems as little as possible. The design and subsequent performance assessment of a minimum-disturbance repository will require an understanding of the thermal-mechanical-hydrological-chemical systems and disturbances, and the ability to predict the response to repository induced perturbations. Laboratory data are necessary to complete our understanding of the phenomena which will allow us to create predictive models. Both conventional laboratory tests and new tests will be required to accomplish the goal of creating predictive models. The purpose of this paper is to review the role of laboratory testing for the characterization of host rocks for nuclear waste repositories. Laboratory testing related to characterization of salt, basalt, tuff, and granite is considered. Expected repository conditions for each host rock type are briefly reviewed in order to summarize induced stress, temperature, groundwater, in-situ stress, etc. conditions anticipated in waste repositories. Current work on the development of constitutive equations appropriate for expected repository environmental conditions is reviewed. In addition, we review laboratory testing to provide input for understanding deformation mechanisms, developing constitutive equations, and evaluation of constants within those equations. Finally, areas requiring further development are discussed and conclusions are drawn. Heard (1979), Handin (1980) and Handin and Heard (1980) have discussed the need for laboratory measurements and their current status. Heard considers six catagories: 1. Elastic properties, 2. Time-dependent mechanical properties (creep), 3. Frictional behavior on discontinuities, 4. Permeability and hydraulic conductivity, 5. Thermal properties, and 6. Deformation and transport mechanisms. Handin and Heard present a table rating the current state of the laboratory-data base and find our overall understanding poor for nonsalt-host-rocks but generally better for salt in most of the four catagories which reflect dependence on effective confining pressure, temperature, time, and water saturation. Progress has been made during the past four to five years as will be presented below. However, space limitations prevent us from covering the entire spectrum of applicable laboratory characterization. Therefore, we will concentrate our efforts on deformation mechanisms and laboratory input for constitutive law development.
