Analysis of a proposed NNWSI exploratory shaft slot test for tuff response

Yucca Mountain in Nevada has been chosen as a potential site for a commercial nuclear waste repository. Sandia National Laboratories is participating in a program to investigate the feasibility of the Yucca Mountain site. One aspect of that study will be an exploratory shaft in Yucca Mountain in which several experiments will be fielded to gain information to assist in the feasibility assessment. This report describes a set of analyses of one of the experiments that has been proposed for the exploratory shaft. The experiment involves cutting a slot in the rock, in this case a densely welded tuff, and pressurizing the slot via a flatjack inserted in the slot. It is anticipated that information on the in situ stress state and strength of the tuff and information useful for verification of analytical techniques will be obtained in the experiment. It is also possible that a relationship between force and deformation for the tuff can be determined. These analyses demonstrated that the experiment could be performed as described in the test plan. The compliant-joint modeling technique that was developed for the project was shown to produce reasonable results in this type of analysis. Several issues of geomechanical modeling were brought out and addressed through the course of the analyses. As a result of the analyses, when more definitive properties for the tuff and the exact geometry of the experiment are known, it will be relatively easy to develop pretest predictions for the behavior of the tuff in the pressurized slot experiment. These predictions can then be compared to the actual behavior for verification of the analysis technique. 13 refs., 37 figs