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within the exposed highwalls (readily mappable) and observed within the South <br /> Quarry boreholes. <br /> • The recommended final highwall configuration within the east(west facing) <br /> highwalls consists of 40H:40V benches for the full planned depth of the mine. This is <br /> a result of the foliations within the granitic and biotite gneiss trending in an adverse <br /> manner, i.e. dipping out of the east highwall. This results in significantly reduced <br /> slope stability. <br /> • The interbench highwalls are anticipated to be near vertical (85°from horizontal)per <br /> discussion with Al. While this configuration results in acceptable highwall stability, <br /> GEI recommends that, wherever possible,this angle be less (-70° recommended)to <br /> decrease the effects of local kinematic failures in addition to freeze-thaw weathering <br /> and resultant highwall spalling. This would also serve to increase the overall stability <br /> of the highwalls. <br /> 6.1.1.2 West Quarry <br /> GEI's recommendations for West Quarry highwall configurations are presented below: <br /> • The recommended final highwall configuration within the whole West Quarry(north <br /> and east facing) below El. 7,000 feet consists of up to 30H:70V (horizontal:vertical) <br /> benches. These areas exhibited favorable geological conditions within the exposed <br /> highwalls (readily mappable) and observed within the West Quarry boreholes. <br /> • The interbench highwalls are anticipated to be near vertical (85°from horizontal) per <br /> discussion with Al. While this configuration results in acceptable highwall stability, <br /> GEI recommends that, wherever possible, this angle be less (-70° recommended)to <br /> decrease the effects of local kinematic failures in addition to freeze-thaw weathering <br /> and resultant highwall spalling. This would also serve to increase the overall stability <br /> of the highwalls. <br /> 6.1.1.3 Sillimanitic Gneiss <br /> In areas where the sillimanitic gneiss is present within any highwall (active mine front or <br /> final) at any thicknesses, special care should be taken as this material has been identified as <br /> containing the significantly weaker(and secondarily metamorphosed) metasomatized gneiss, <br /> which is more unstable than the surrounding gneisses. Minor structural instabilities have <br /> been noted in mine front highwalls where this material is exposed by mining activities. The <br /> nature and extent of these failures is not part of the scope of this project, however, it is <br /> believed that the weak rock may fail by"crushing"when adjacent material is removed and <br /> subsequent blasting (impact shaking) disrupts the in-situ material. Therefore, wherever <br /> sillimanitic gneiss is observed in highwalls, the area should be considered unstable, until <br /> geotechnical confirmation/evaluations can be conducted. <br /> Sillimanitic gneiss has been observed exposed within South Quarry and West Quarry and <br /> within borings advanced during various phases of quarry design with varying thicknesses <br /> noted. Areas where the sillimanitic gneiss is one-quarter of the bench height, the entire <br /> Aggregate Industries Morrison Quarry GEI Consultants. Inc. <br /> AM-06 Geotechnical Stability Exhibit 39 August 2018 <br />