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' and anticlines from approximately 50 to 200 ft across. As a result of <br /> this rock structure, the strike of the foliation joints varies from about <br /> N50E to N50W, but is generally north-south to approximately N20W. <br /> ■ Spacing of joints in the primary joint set typically ranges from several <br /> inches to approximately three ft. Joint surfaces vary greatly from <br /> fresh to highly-weathered and/or slickensided. Weathered schist <br /> interbeds parallel to primary jointing having a slick and weak <br /> character are frequent throughout the rock mass. <br /> ■ The predominant dip angle of the primary joint set is usually at or <br /> 1 slightly steeper than the approximately 35 degree inclination of the <br /> overall slope and, as a result, the joints typically plunge into the <br /> slope. The joints daylight, however, on the vertical and near vertical <br /> individual highwalls. Some foliation dip angles are as shallow as 20 <br /> to 25 degrees, locally. <br /> ■ At least two secondary joint sets are present, often orthogonal with <br /> the primary joint set. These secondary joints typically occur at <br /> intervals of one to five ft and are typically near vertical to very <br /> steeply dipping. In general, secondary joint surfaces are planar, are <br /> fresher and less weathered than the primary joints along foliation, and <br /> do not exhibit the smooth schistose or micaceous surfaces. The <br /> secondary joints are also locally discontinuous, terminating at primary <br /> joints. <br /> ' ■ The slope of the debris below the newly-excavated benches was <br /> measured at a dip of approximately 40 to 45 degrees from horizontal <br /> and represents the temporary angle of repose of this material. <br /> ■ Localized block and wedge failures of the outside edges of the third <br /> and fourth benches are common but less prevalent than in the upper <br /> two benches. This difference in behavior is attributed to the sloped <br /> ' highwalls (from the angle drilling) and from the lesser degree of <br /> weathering of the rock material at greater depth within the rock mass. <br /> Based on the conditions observed with the present exposures, the rock mass <br /> exposed is consistent with the conditions used as the baseline for analyses of <br /> the East Highwall, except for the presence of old weathered shear surfaces <br /> ' revealed by the localized slide failure that occurred. <br /> B. Slide Failure Area <br /> 1. General <br /> ' One of the primary concerns recognized during previous evaluations <br /> of the East Highwall was that a large-scale preexisting joint or shear <br /> ' 9 G:\PROJECTS\20200\002\96ANNRPT.WPD <br /> '� e <br />