Rock Mass Mechanical Property Estimation Strategy for the Yucca Mountain Site Characterization Project

by M. Lin, J.F.T. Agapito & Associates, Inc, Grand Junction, United States,
C. E. Brechtel, J.F.T. Agapito & Associates, Inc, Grand Junction, United States,
M. P. Hardy, J.F.T. Agapito & Associates, Inc, Grand Junction, United States,
S. J. Bauer, J.F.T. Agapito & Associates, Inc, Grand Junction, United States,

Document Type: Proceeding Paper

Part of: High Level Radioactive Waste Management 1993


Rock mass mechanical properties are required in the design of repository drifts and ramps to assess the impact of thermal loads from the heat-generating wastes on excavation performance and long-term structural stability. The ramps, exploratory drifts and repository excavations will intersect both welded and nonwelded tuffs with varying abundances of fractures, degree of welding and lithophysal content. Rock mass mechanical properties are dependent on both intact rock properties and joint characteristics, and were derived from empirically based relationships of laboratory determined intact rock properties and rock mass quality indices (Q and RMR). Definition and verification of these empirical relationships is considered critical to the drift design methodology because planned thermomechanical testing in the Exploratory Studies Facility (ESF) is limited. Rock mass quality determinations may provide the only practical vehicle for assessment of the effects of variability in drift performance under thermal loads. This paper presents a method of estimating the rock mass properties for the welded and nonwelded tuffs based on currently available information on intact rock and joint characteristics at the Yucca Moutain site. Variability of the expected ground conditions at the potential repository horizon (the TSw2 thermomechanical unit) and in the Calico Hills nonwelded tuffs is accommodated by defining five rock mass quality categories in each unit based upon assumed and observed distributions of the data.

Subject Headings: Rock properties | Rock masses | Thermal loads | Mechanical properties | Radioactive wastes | Thermal properties | Drift (structural) | Excavation | Nevada | United States

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