The in situ stress field was determined at a depth of 837 m (2745 feet) in Devonian Shale ('gray' shale) within the Rome Basin in West Virginia. Logging data and laboratory observations of core samples reveal vertical cracks oriented at N50ø-60øE. Because of these cracks and their preferred orientation a new approach based on fracture mechanics concepts is used to evaluate the in situ stresses from the field and laboratory data. The resulting prediction of the maximum horizontal stress (a•tmax) is compared to the maximum horizontal stress predicted by Haimson and Fairhurst's (1967) method; the latter method appears to overestimate the value of this stress component because the effect of loading the faces of any preexisting crack is neglected. ..... 2851

No abstract

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^

No abstract

No abstract