Laserfiche WebLink
The trends of the lines of intersection that can daylight onto the slope have been identified <br />with arrows on the stereonets for each of the wall orientations (Figures 11 -16). Based on <br />the results discussed in Section 4, the limiting resistance to sliding is drawn as a dashed <br />circle on the stereonets having a radius equivalent to a friction angle of 33°. Markland's <br />two criteria for sliding are satisfied when the intersection of the discontinuities plot on the <br />stereonets within the hatched regions that are bounded by the friction circle and the great <br />circle representing the plane of the slope face. Further evaluation of the stereonet plots <br />can 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 and the <br />dip direction of either of the surfaces forming the intersection falls between the dip <br />direction of the slope face and the trend of the line of intersection, then sliding will occur <br />on that plane rather than along the line of intersection. The following four conditions, <br />defined by Hoek & Bray (1977), must 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 slope <br />face. <br />' 2) The failure plane must "daylight" in the slope face (i.e. the dip of the plane must be <br />smaller than the dip 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 <br />rock mass to define the lateral boundaries of the slide. <br />As indicated earlier, the data for each set cluster around the representative value that is <br />plotted on the stereonets. To illustrate the possible variation in discontinuity dip angles and <br />directions, and how this can affect the interpretations and conclusions that can be made, <br />multiple foliation discontinuity dip angles have been drawn for F-1 on each stereonet. The <br />alternate foliation dip angles for F-1 correspond to one standard deviation above and <br />below the mean dip angle of 36° (i.e., 46° and 26°). <br />-14- <br />tachei & Associates <br />A $CNNA8E1 r-'GINEFRING COMPANY