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• MLESIopeDesign <br />4. CONSTRUCTION <br />Construction of the mine walls to the design slopes presented in Table 1 requires the following <br />excavation techniques. <br />4.1 Blasting <br />Specialized slope blasting will minimize disturbance of the final wall, and the final benches. The <br />Cresson slope blasting design draws on experience in blast testing in the Main Cresson Mine (Itasca, <br />1999; ABC, 2003), and has been found to be effective in the District. Features of the blasting method <br />are: <br />1. Light trim or pre-split blasting against the final wall, with close-spaced holes (maximum 5 feet) <br />to ensure that atrim/split line will develop in all rock types. <br />2. Two foot sub-drilling at the toe of the slope to prevent the formation of a hard toe, which results <br />in a "wedge" at the base of the toe that can result in any falling rock being propelled laterally out <br />onto the working level. <br />3. Avoidance of disturbing the next bench crest by: <br />• a. Aligning blast hole lines so that the next crest falls equidistant from two blast hole lines. <br />b. Not sub-drilling blast holes on the two lines that straddle the future crest location. <br />4. Loading the holes in the vicinity of the final wall and bench as lightly as is consistent with <br />required breakage. <br />Final walls can be formed using trim or pre-split blasting: <br />Pre-split. If pre-split blasting to form the wall is chosen, this row should be shot prior to mining <br />on the level from which it is drilled. Bench mining on the same level as the pre-split that is <br />conducted prior to forming the pre-split should maintain a minimum of three parallel rows from <br />the presplit line to ensure good containment of the pre-split blast. The pre-split detonation order <br />should be such as to sweep from one end of the blasthole line to the other. <br />2. Trim. If trim blasting against the wall is chosen, the row should be shot last in the bench round, <br />with delays to result in a sweep blast from one end to the other. <br />4.2 Scaling <br />Safe slopes mined at the angles indicated in Table 1 require effective scaling. Scaling removes loose and <br />hanging material from the slope, so that subsequent raveling is minimized. <br />Scaling is conducted at the Cresson Project by a long-boom excavator, physically picking loose and <br />overhanging rock from the exposed final walls of the mines. <br />• <br />Report 1385E.20080411 g <br />