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rock mass is characterized with field and/or laboratory studies, and the actual conditions compared with <br /> the assumed baseline conditions to re-evaluate slope stability. <br /> The two baseline conditions previously analyzed and presented were for "competent rock" representing <br /> the majority of expected conditions, and for "poor rock" representing localized areas of shearing, <br /> weathering, or adverse jointing. Typical in-situ rock mass characteristics for each of these baseline <br /> conditions and the corresponding strength envelopes and calculated safety factors are presented in Permit <br /> Amendment No. 3, Section 4-04. <br /> Based on recent rock mass data obtained during 1994, including the borings, laboratory testing, and field <br /> mapping, it was determined that the rock exposed along west highwall meets the previously defined <br /> characteristics for "competent rock". This assessment was based on: <br /> 1. An average unconfined compressive strength of 19,500 psi for representative specimens, <br /> and 14,000 psi for all specimens including specimens chosen specifically to represent the <br /> worst case condition. <br /> 2. Jointing on recurrent intervals of approximately three inches to five feet. <br /> 3. Joint faces are predominately fresh or clean, and occasionally with minor weathering or <br /> coatings as a percentage of overall joint surface area. <br /> 4. The core recovered from the borings had an average recovery of 97 percent and an <br /> average RQD of at least 70 to 75 percent for representative conditions, and 55 percent <br /> including blast damaged zones and boring CH-CR4 representative of poor quality <br /> conditions. <br /> 5. The primary joint set parallel with the gneissic foliation dips into the slope of the <br /> highwalls on the west side of the quarry. <br /> Previous baseline slope stability evaluations of overall slopes using a rock mass characterized as <br /> "competent" resulted in adequate safety factors for slopes having inclinations as steep as 0.5H:1V and <br /> up to 750 ft high. The western slope has an overall inclination of approximately 1H:1V from top to <br /> bottom and a present total height of approximately 470 ft. Therefore, based on a comparison of baseline <br /> with actual conditions, the decision was made to reduce the width of the bench at elevation 6560 to 40 <br /> feet. <br /> In areas where the slope configuration is at or is anticipated to be at 40 ft benches and 80 ft highwalls, <br /> precision perimeter control blasting techniques have been employed by Cooley. These methods have <br /> resulted in relatively minor damage to the rock mass and helped maintain the inherent strength of the rock <br /> mass near exposed faces with a corresponding beneficial effect on slope and bench stability. Precision <br /> blasting techniques will be continued on an as-needed basis and in areas of special concern for stability <br /> (e.g. the East Highwall and at final cut slopes). <br /> M8267.200 7 <br />