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' 4. Release surfaces which provide negligible resistance to sliding must be present in <br /> the rock mass to define the lateral boundaries of the slide. <br /> Photos 4-6 which were taken at varied distances from the north wall were analyzed along <br /> ' with the stereonet plot to determine if these four criteria were satisfied. <br /> Relative to the first criterion, the shaded pole on the stereonet plot representing the slope <br /> face, and the pole labeled P-1 representing the orientation of the rock mass foliations are <br /> twithin 4 degrees of each other (i.e. essentially identical). Secondly, the dip of the,plane <br /> (of the foliation) is 46 degrees, and the dip of the slope face is 45 degrees. While the <br /> ' second criterion states that the "dip of the plane must be smaller than the digs of the slope <br /> face", the dip of the foliations is variable (see Figure 3) and Photos 4-6 verify the <br /> ' "daylighted"failure surfaces. <br /> The third criterion is satisfied, based on the assumption that the angle of friction is equal <br /> to 40 degrees. Though this value may be conservative, no data was available to <br /> substantiate an increase in this assumed value. <br /> ' The fourth and final criterion is critical to the actual release of planes for sliding. Release <br /> ' surfaces must be present to define the lateral boundaries of the slide. These release <br /> surfaces, formed by intersecting joint sets, are most evident in Photo 6 and are identified <br /> ' on the stereonet plot by poles P-2, P-3, and P-4. <br /> Though this mechanism for failure plane development has been quantified in this analysis, <br /> there are several additional factors that must be included in an assessment of the overall <br /> rstability for the north wall. The general "waviness" of the foliation in the rock mass (as <br /> seen in Photo 7) serves to limit the length of possible failure planes. For large failures to <br /> occur, the failure surface must pass through zones of intact rock as well as along the <br /> weaker foliation discontinuities. Also, the absence of ground water and associated <br /> ' 15 <br />