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L~ <br /> <br /> <br />1 <br /> <br /> <br /> <br />1 <br /> <br />C~ <br /> <br /> <br /> <br /> <br /> <br />LJ <br /> <br /> <br /> <br />the stereonets within the hatched regions that are bounded by the friction circle <br />and the plane of the slope face. Further evaluation of the stereonet plots can <br />then identify the specific discontinuity surfaces where sliding may occur. <br />Planar failure is a special case of wedge failure. If Markland's criteria is satisfied <br />and the dip direction of either of the surfaces forrning the intersection falls <br />between the dip direction of the slope face and the trend of the line of <br />intersection, then sliding will occur on that plane rather than along the line of <br />intersection. The following four conditions, defined by Hoek & Bray (1977}, must <br />be met in order for true planar failure to occur: <br />1) The plane on which sliding occurs must strike parallel or nearly parallel to the <br />slope face. <br />2) The failure plane must "daylight" in the slope face (i.e. the dip of the plane <br />must be smaller than the dip of the slope tace). <br />3) The dip of the failure plane must be greater than the angle of friction of the <br />plane. <br />4) Release surfaces, which provide reduced resistance to sliding, must be <br />present in the rock mass to define the lateral boundaries of the slide. <br />6.2.1 East Wall <br />Historically, the east wall has had no major instability issues. The stereonet plot <br />for the east wall was derived from the full dataset (Figure 11) shows four plunges <br />of lines of intersection less than the angle of the slope face, resulting in the <br />interpretation that the potential for sliding exists along these intersections. <br />However, all of the wedges indicate that sliding will not occur unless friction <br />angles are less than 33°, therefore showing that they are stable for the existing <br />45° slope angle. <br />The stereonet plot also show that F-1 and F-2 intersect, resulting in a plunge of <br />line of intersection less than the angle of the slope face and indicating the <br />potential for sliding. The emergence of F-2 as a definitive discontinuity set has <br />_ya_ <br />