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• -28- <br />2. Some existing slopes are presently steeper than 1.5:1. Those slopes <br />should be flattened in the vicinity of the experimental mine pit <br />floor. We recommend that a 1.5:1 slope ratio be maintained for a <br />distance of at least 100 feet each side of the outermost entries to <br />provide a buffer zone. <br />3. We recommend that the slope be monitored for movement. This program <br />should include installation of targets placed at about 100 feet on <br />centers near the slope crest, mid - height and near the toe. Inspec- <br />tion for movement and occurrence of tension cracks should be made <br />at least quarterly and preferably monthly. <br />4. Observation should be made during grading for occurrence of fire <br />clay. This observation can be made by mine personnel during con- <br />struction but a representative of our office should be present on <br />a periodic basis. <br />5. The slope.should be flattened to at least 2; horizontal to 1 vertical <br />after a period of 5 years or, if frequent shallow failures or slope <br />movement is detected. <br />• Long -Term Slopes <br />1. At the end of about 5 years or prior to construction of the full - <br />scale underground mine, spoil slopes should be flattened to an over- <br />all ratio of 2 horizontal to 1 vertical. Our stability analysis <br />indidates a factor of safety for mass failure of 1.5, or greater, <br />for this slope ratio. <br />2. Flattening of the slope can be achieved by either grading the entire <br />slope to a continuous ratio of 2:1 or by providing 30 -foot wide <br />benches at 50 -foot vertical intervals with 1.5:1 intermediate slopes. <br />Both of these configurations should consider economics and construc- <br />tion feasibility. <br />3. The benching configuration with 1.5:1 individual slopes should only <br />be selected if some shallow failures can be tolerated and protection <br />at mine entries provided. <br />4. Observation should be made during grading for the presence of fire <br />clay. This observation can probably be best made by mine personnel <br />during construction, however, a representative of our office should <br />be present on a periodic basis. <br />5. A permanent slope inspection program should be instituted to observe <br />for occurrence of tension cracks and evidence of slope creep. We <br />believe that inspections should be made at least quarterly. <br />