Geology of the ECRB Cross Drift-Exploratory Studies Facility, Yucca Mountain Project, Yucca Mountain, Nevada
The Enhanced Characterization of the Repository Block Cross Drift (Cross Drift) excavated at Yucca Mountain is being studied to determine its suitability as a permanent high-level nuclear waste repository. This report presents a summary of data collected by the U.S. Bureau of Reclamation (USBR) personnel on behalf of the U.S. Geological Survey (USGS) for the Department of Energy in the Cross Drift from Sta. 00+00 to 26+64. This report includes descriptions of lithostratigraphic units, an analysis of data from full-periphery geologic maps (FPGM) and detailed line survey (DLS) data, a detailed description of the Solitario Canyon Fault zone (SCFZ), and an analysis of geotechnical and engineering characteristics. The Cross Drift is excavated entirely within the Topopah Spring Tuff formation of the Paintbrush Group. Units exposed in the crystal-poor member of the Topopah Spring Tuff, include the Topopah Spring crystal-poor upper lithophysal zone (Tptpul) (Sta. 0+00 to 10+15), the Topopah Spring crystal-poor middle nonlithophysal zone (Tptpmn) (Sta. 10+15 to 14+44), the Topopah Spring crystal-poor lower lithophysal zone (Tptpll) (Sta. 14+44 to 23+26), and the Topopah Spring crystal-poor lower nonlithophysal zone (Tptpln) (Sta. 23+26 to 25+85). The lower portion of the Topopah Spring crystal-rich lithophysal transition subzone (Tptrl1) is exposed on the west side of the Solitario Canyon fault from Sta. 26+57.5 to 26+64. Lithologically, the units exposed in the Cross Drift are similar in comparable stratigraphic intervals of the Exploratory Studies Facility (ESF), particularly in terms of welding, secondary crystallization, fracturing, and type, size, color, and abundance of pumice and lithic clasts. The most notable difference is the lack of the intensely fractured zone (IFZ) in the Cross Drift. The as-built cross section and the pre-construction cross section compare favorably. Lithostratigraphic contacts and structures on the pre-construction cross section were encountered where expected. Discrepancies occur at Sta. 22+38 where an unexpected fault was encountered, and in the hanging wall of the SCFZ where west-dipping beds were predicted but not encountered. Also, the pre-construction cross section did not predict the Tptpul/Tptrl contact exposed at Sta. 26+57 of the Cross Drift. The SCFZ has two major normal fault strands, the eastern strand (main splay) and the western strand. The eastern strand has approximately 260 m of normal offset based on stratigraphic relationships and the as-built cross section. The western strand was not penetrated by the tunnel boring machine (TBM) based on programmatic decisions to cease tunnel advancement. The as-built cross section estimates the offset on the western strand to be about 68 m. Footwall deformation in the SCFZ was greater than anticipated by the Geotechnical Baseline Report. The blocky and raveling ground encountered in the footwall was predicted to be more likely to occur in the hanging wall. This may indicate a broad zone of deformation associated with the intersection of additional splays with the eastern strand of the SCFZ.
- Research Organization:
- Yucca Mountain Project, Las Vegas, NV (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- AI08-92NV10874
- OSTI ID:
- 763121
- Report Number(s):
- Milestone SPG42GM3; TRN: US0108971
- Resource Relation:
- Other Information: PBD: 1 Jan 1999
- Country of Publication:
- United States
- Language:
- English
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