HR: 1340h
AN: T23B-0545    [Abstracts]
TI: Synthesis of Subsurface Fracture Characteristics at Yucca Mountain, Nevada
AU: * Smart, K J
EM: ksmart@swri.org
AF: Department of Earth, Material, and Planetary Sciences, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238-5166 United States
AU: Wyrick, D Y
EM: dwyrick@swri.org
AF: Department of Earth, Material, and Planetary Sciences, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238-5166 United States
AU: Landis, P S
EM: plandis@swri.org
AF: Center for Nuclear Waste Regulatory Analyses, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238-5166 United States
AU: Waiting, D J
EM: dwaiting@swri.org
AF: Center for Nuclear Waste Regulatory Analyses, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238-5166 United States
AB: Fractures are among the most abundant geologic structures found in rocks. Although individual fractures are rarely of great importance, the sheer number of fractures makes them a key component of many geologic and engineering-related processes. Fractures directly affect geotechnical processes for stability of underground openings and indirectly influence processes such as thermal stress accommodation. Near-surface water infiltration and flow, and unsaturated zone radionuclide transport are tunnel- and mountain-scale processes influenced by fractures. Yucca Mountain, Nevada is the site of the United States' potential high-level nuclear waste repository. This presentation provides an up-to-date synthesis of subsurface fracture data collected in the repository host horizon interval from two tunnels, the Exploratory Studies Facility (ESF) and the Enhanced Characterization of the Repository Block (ECRB) cross-drift at Yucca Mountain. The primary goals are to: (1) summarize fracture data collected by both detailed line survey and full-periphery geologic mapping techniques; and (2) provide a rigorous analysis of key fracture characteristics, including fracture orientation, spacing and size. Definitive cooling joints and vapor phase partings are present in all zones within the Topopah Spring Tuff (the proposed repository host horizon), but are not abundant and represent only 5 to 11% of all recorded fractures. Fractures with measurable displacement are also present, but account for only 3 to 4% of the total population. These fractures, however, are predominantly subvertical with either a northwest or northeast strike. Regardless of lithostratigraphic interval (i.e., presence or absence of lithophysae), distinctive orientation-based fracture sets are present -- fractures are not randomly distributed. This observation holds for analyses of long and short fractures. The overall distribution of fracture size based on observed trace length is strongly skewed with short fractures significantly more abundant that long fractures. The most prominent fracture set throughout most of the area is a northwest-striking subvertical set, but a subhorizontal set is also present. In addition, one or more additional steeply dipping fracture sets are observed. Overall one- and two-dimensional fracture intensities are highest in the nonlithophysal zones. In general, the northwest-striking subvertical fracture set has the highest intensity value. The subhorizontal fracture set in the lithophysal zones shows high intensity values after corrections for sampling bias introduced by the subhorizontal tunnel orientations are performed. Orientation and intensity data derived from full-periphery geologic mapping in the ECRB Cross-Drift confirm observations based on detailed line survey data. This abstract was prepared to document work performed by the Center for Nuclear Waste Regulatory Analyses (CNWRA) and its contractors for the Nuclear Regulatory Commission (NRC) under Contract No. NRC-02-02-012. The activities reported here were performed on behalf of the NRC Office of Nuclear Material Safety and Safeguards, Division of High-Level Waste Repository Safety. This abstract is an independent product of the CNWRA and does not necessarily reflect the view or regulatory position of the NRC.
DE: 1859 Rocks: physical properties
DE: 5104 Fracture and flow
DE: 8010 Fractures and faults
DE: 8015 Local crustal structure
DE: 8025 Mesoscopic fabrics
SC: Tectonophysics [T]
MN: Fall Meeting 2005