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Martin Marietta Materials <br />Spec -Agg Project <br />According to Markland's test, sliding can occur when: <br />1) The plunge of the lines of intersection is less than the dip of the slope face. <br />2) The plunge of the lines of intersection exceeds the angle of friction. <br />The trends of the lines of intersection that can daylight onto the slope have been identified with arrows on the <br />stereonets for each of the wall orientations (Figures 11 -16). Based on the results discussed in Section 4, <br />the limiting resistance to sliding is drawn as a dashed circle on the stereonets having a radius equivalent to a <br />friction angle of 33 °. Markland's two criteria for sliding are satisfied when the intersection of the <br />discontinuities plot on the stereonets within the hatched regions that are bounded by the friction circle and <br />the great circle representing the plane of the slope face. Further evaluation of the stereonet plots can then <br />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 and the dip direction of <br />either of the surfaces forming the intersection falls between the dip direction of the slope face and the trend <br />of the line of intersection, then sliding will occur on that plane rather than along the line of intersection. The <br />following four conditions, defined by Hoek & Bray (1977), must be met in order for true planar failure to <br />occur: <br />1) The plane on which sliding occurs must strike parallel or nearly parallel to the slope face. <br />2) The failure plane must "daylight" in the slope face (i.e. the dip of the plane must be smaller than the dip <br />of the slope face). <br />3) The dip of the failure plane must be greater than the angle of friction of the plane. <br />4) Release surfaces, which provide negligible resistance to sliding, must be present in the rock mass to <br />define the lateral boundaries of the slide. <br />As indicated earlier, the data for each set cluster around the representative value that is plotted on the <br />stereonets. To illustrate the possible variation in discontinuity dip angles and directions, and how this can <br />affect the interpretations and conclusions that can be made, multiple foliation discontinuity dip angles have <br />been drawn for F -1 on each stereonet. The alternate foliation dip angles for F -1 correspond to one standard <br />deviation above and below the mean dip angle of 36° (i.e., 46° and 26 °). <br />5.2.1 East Wall <br />Historically, the east wall has shown no major instability issues. The stereonet plot for the east wall was <br />derived from the full dataset and shows multiple plunge lines of intersection less than the angle of the slope <br />face and one intersection that falls within the failure envelope (Figure 11). Consequently, the potential for <br />sliding exists along one set of intersecting planes. Foliation plane F -3 and joint P -5 are the only planes <br />having a line of intersection that not only daylights the pit wall, but also plunges at an angle steeper than the <br />angle of friction. Therefore, if this intersection of planes exists in the eastern wall area, sliding is <br />kinematically possible. All other plunge lines of intersecting planes that daylight the pit wall are inclined at an <br />angle less than the angle of friction, and therefore are considered to be kinematically stable. <br />For the temporary nearly vertical bench face (prior to reclamation), additional potentially unstable wedges <br />may exist due to the steep overall slope angle (e.g. P3:P1 and P4:P1). These wedge failures have been <br />observed occasionally on the east wall and are localized in extent. The development and size of these <br />February 13, 2012 Page 10 Lachel & Associates, Inc. <br />Project 11361017.00 ©2012 All Rights Reserved <br />