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Geotechnical Characterization of the Main Drift of the Exploratory Studies Facility was based on borehole data collected in site characterization drilling and on scanline rock mass quality data collected during the excavation of the North Ramp. The Main Drift is the planned 3,131-m (10,273-ft) near-horizontal tunnel to be excavated at the potential repository horizon for the Yucca Mountain Site Characterization Project. Main Drift borehole data consisted of three holes -USW SD-7, SD-9, and SD-12-drilled along the tunnel alignment. In addition, boreholes USW UZ-14, NRG-6, and NRG-7/7A were used to supplement the database on subsurface rock conditions. Specific data summarized and presented included lithologic and rock structure core logs, rock mechanics laboratory testing, and rock mass quality indices. Cross sections with stratigraphic and thermal-mechanical units were also presented. Topics discussed in the report include geologic setting, geologic features of engineering and construction significance, anticipated ground conditions, and the range of required ground support.Rock structural and rock mass quality data have been developed for each 3-m (10-ft) interval of core in the middle nonlithophysal stratigraphic zone of the Topopah Spring Tuff Formation. The distribution of the rock mass quality data in all boreholes used to characterize the Main Drift was assumed to be representative of the variability of the rock mass conditions to be encountered in the Main Drift. Observations in the North Ramp tunnel have been used to project conditions in the lower lithophysal zone and in fault zones. DISTRIBUTION O^ TWIS r>or,UMENT IS UNLIMITED^

The following qualified computer software items were used in parts of this design confirmation analysis. 6.1.1 Fast Lagrangian Analysis of Continua (FLAC), Version 3.30 (Reference 5.17) was used to calculate the geometry factor for the back calculation of the rock mass modulus of deformation. The analyses were performed on a computer with a Pentium microprocessor. FLAC software is appropriate for the applications used in this design confirmation analysis. FLAC was obtained from the Software Configuration Management (SCM) in accordance with the applicable M&O procedures. FLAC software was used only within the range of validation as specified in the software qualification documentation (Reference 5.17). A complete listing of input files used in this analysis is provided in Attachment V. Detailed description of FLAC and its fields of application are presented in Reference 5.17. The outputs are presented and described in Section 7.