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r' <br />-, <br />~. . <br />• <br />Main CressonSlopeEvaluation <br />AdrianBrown <br />5.2 North Mine <br />5.2.1 Joint Sets <br />The north mine area contains the most complex joint system observed in the mine. The principal joint <br />sets are shown in Figure 6, and are contoured in Figure 7. The principal joint sets are as follows: <br />North dip direction/60° dip (East-West strike, 60°to the north). This joint set dips into the <br />north wall on an approximately east-west strike at an angle of about 45°-60°. This set may be <br />made up of two sepazate lobes which overlap. Joint sets dipping in this range are raze in the <br />remainder of the mine. This joint set might form a possible toppling joint set along the north <br />wall of the North Mine, although no movement of this kind is currently evident on the <br />existing north wall. <br />2. Dip direction 210°/50° dip (Northwest-Southeast strike, 50° dip to the southwest). This <br />joint set strikes approximately normal to the north mine wall, and dips to the south-west at an <br />intermediate angle. Again, joint sets at this dip are unusual in the rest of the mine. <br />3. Dip direction 90°/90° dip (North/south strike, 90° dip [vertical]). There is a <br />predominantly vertical joint set, with an approximately north-south strike (although the data <br />• could support two adjacent joint sets). <br />As the data for this evaluation has been collected almost entirely from walls oriented N60°E, there may <br />be some lack of representation of joints which strike in that direction. None of the joint sets which have <br />been identified represent significant failure potential for the slope. <br />5.2.2 Fracture Intensity <br />Based on visual observation of the wall, and on the number of joint sets which are logged on the wall <br />(Figure 8), fracture intensity in the north mine is high (averaging approximately one fracture per foot). <br />As a result, joints exhibiting each of the principal orientations described above occur relatively close <br />together. This increases the ability of the joint sets to intersect to form wedges and blocks. Further, the <br />average block size on the wall is small, in the order of 1 to 10 cubic feet. <br />5.2.3 Structural Stability <br />The structural stability of the wall has been evaluated in Figure 8. This shows the polar domains in <br />which structural failure could occur overlain on the structural information, by type. The structural failure <br />conditions are: <br />1. Sliding Failure. The domain on the polar projection which represents possible sliding failure <br />is shown as being sub-pazallel to the wall orientation, and representing all features which <br />• 5 Note: All joint set information is given in this report in the form DD/Dip, where DD is the dip direction in degrees bearing (clockwise <br />from north), and Dip is the dip in degrees, with 0 representing horizontal, and 90 representing vertical. To assist clarity, the strike/dip <br />format, in direction/degrees form, is included in brackets following the dip direction/dip presentation. <br />1385D.980612 18 <br />