Laserfiche WebLink
•, r_ <br />{r <br />• <br />Main CressonSlopeEvaluation <br />AdrianBrown <br />have a dip angle between 40° (the effective stress friction angle for sliding on joint surfaces <br />determined in Section 3.3 above), and 60° (the maximum slope angle which is geometrically <br />feasible in this mine). As essentially no poles fall within this potential sliding zone, it is <br />concluded that sliding failure is very unlikely, based on the information to date. In other <br />words, there aze essentially no observed fractures which have the potential to create a sliding <br />failure on this wall. No such failures have been observed, although the wall is still relatively <br />small. <br />• <br />2. Toppling Failure. Toppling failure in large mine slopes requires a set of joints or faults <br />dipping into the face at approximately 50° ± 10°. There is one joint set observed on the wall <br />which approaches this orientation, as illustrated in Figure 8, suggesting that toppling failure <br />is possible on this wall. Toppling failure in this case would result in gradual movement of the <br />slope materials, but not necessarily a mass translational movement of material from the slope. <br />Only one of the recorded potential toppling joints is a fault, with the possibility of gouge <br />representing a weak plane on this feature. As the toppling mechanism requires low friction <br />characteristics (typically less than about 15° effective stress friction angle), this is the only <br />feature which falls within the toppling "zone" which might represent a potential toppling <br />failure plane. As there is only one of these features, rather than a family of them, it is <br />considered that toppling behavior on the slope is unlikely. No such movement has been <br />observed, although the wall is still relatively small. <br />3. Kink band failure. In rockmases which are made up of relatively small blocks, it is possible <br />for overall wall failure to occur as a result of the development of a "kink band" along a <br />potential zone of failure (Ladanyi and Archambault, 1970). In this mechanism, small blocks <br />along highly stressed zones which lie along potential failure zones may rotate, resulting in the <br />creation of a weak zone in which the resistance to movement is reduced when compared to <br />failure through the rockmass. The relatively small block size suggest that this wall might be <br />susceptible to this form of failure if there were to be a need to excavate the wall at a steep <br />slopeb. . <br />4. Granulaz failure. The portion of the north wall rockmass which has been excavated to date <br />has been highly fractured. If this condition is found to typify this wall area, the material may <br />behave more like a granular material than an interlocking rockmass, and the resulting bench <br />stability may be poor. In such conditions, the overall wall slope may tend toward the angle of <br />repose of the blocky material, which is expected to be in the order of 40°, and there will be <br />substantial raveling of catch benches. Portions of the wall are already behaving in this <br />manner, based on the excavation to date'. <br />6 At present, the slopes in the north wall are determined by land position and ore grade, and is not particularly steep (Plate 1). <br />• ~ The current location of the north wall is immediately adjacent to a granitic intrusive (Plate 2). This intrusive may have caused <br />disturbance of the north wall material, which may not persist as the wall moves to the north in subsequent push backs. <br />1385D.980612 7 9 <br />