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' V. GEOTECHNICAL ANALYSIS ' 5.01 General ' Specific slope stability analyses were not conducted nor required for mining activities performed during 1998. Rather, observed conditions were compared with assumed baseline conditions used as the basis for design and consistent with the Observational Method. ' Two rock mass conditions were identified for design purposes, and used as the baseline for further evaluations: The two baseline conditions were "competent rock", representing the majority of expected conditions, and "poor rock" representing localized areas of shearing, ' weathering or adverse jointing. Typical in-situ rock mass characteristics and the corresponding strength envelopes and calculated safety factors for each of these baseline conditions were presented in Amendment No. 3, Section 4-04. The general ground conditions observed relative to the baseline conditions fur each of the areas worked are described in the following sections. 5.02 East Side of the Central Quarry ' A. General ' The highwalls and benches are aligned at approximately N25°W to N30°W. This rock is primarily competent rock (unconfined compressive strength greater than 15,000 psi) with localized zones of poor rock. 1 1 The primary joint set along foliation of the gneiss rock has been historically striking sub-parallel with the slope and dips 20 to 60 degrees in a westerly direction, sub- perpendicular to the slope. Analyses of the final highwalls on Benclt 2 and Bench 1 show a slight change in that historic trend. This change was also observed on the final cuts of the final Bench 4 and Bench 3 highwalls, completed in 1997. The historic pattern persists at the north end of Bench 2 and Bench 1 highwall, but varies to striking more sub-perpendicular/perpendicular to the slope along the southern parts of Bench 2 and Bench 1 highwalls. Foliation dip varies from approximately 25 to 45 degrees, with dip directions generally to the northwest on the northern section of the high walls and [o the southwest in the southern section of the high walls. The sub- perpendicular to perpendicular strike orientation is a more favorable for slope and highwall stability. Spacing of joints in the primary joint set typically ranges from several inches to approximately 3 ft. Joint surfaces vary greatly from fresh and tight, to highly weathered and open with clay-infilling. Weathered schist interbeds parallel to primary jointing having a slick and weak character were not as frequently detected as in higher benches. The predominant dip angle of the primary joint set is slightly steeper than the approximately 35 degree inclination of the overall slope. The joints, where the strike is sub-parallel to the slope, typically parallel or plunge into the slope. However, [he joints frequently daylight, on the vertical and near vertical individual highwalls. ' G:\PROIECfS\30200 Normm~ Quarry\003\Amu>I Repon GmISMICaf AdEendum\1998\98gr mukup.da Page 6