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The minimum factors of safety calculated are as follows: <br />Pit Depth <br />"F" Seam - Static <br />Pseudo-Static <br />"J" Seam - Static <br />~~ <br /> <br />r- <br />L <br />L <br />Minimum Factor of Safety <br />30o Slope 45° Slope 60° Slope <br />2.41 1.98 l..i'? <br />1.81 1.56 1.14. <br />1.81 1.33 0.75 <br />1.41 1.08 0.60 <br />The limited quantity of some data and the lack of other data necessitates <br />making several important assumptions on ground water and structural control. <br />The calculated factors of safety are real values only to the extent that <br />the assumptions do, in fact, reflect the real field condition. <br />4. Rock Rippability and Type of Shovel Tooth <br />Engineering evaluation of rock quality and physical and mechanical pro- <br />perties indicate that most rock units in this area could be ripped with <br />conventional rippers. The exception to this is in some portions of the <br />sandstone units. The sandstones, particularly those with fine to very <br />fine grains, probably can be more economically broken by conventional <br />blasting than by ripping, depending on the thickness of the unit. However, <br />locally the sandstones are weathered and become weak and brittle which <br />makes them suitable for ripping. The powder factor for blasting the sand- <br />stone would range from 0.4 to 0.5 pounds of ANFO per ton of rock. The <br />blasting pattern should be determined at the site when the mining has <br />progressed to the sandstone layers. Because the mine would require both <br />blasting and ripping, the shovel bucket should be of a curved lip type <br />with wear cap teeth to compensate for the abrasion by the hard sandstone. <br />L C. RECOP4fENDATI0N5 <br />The follo•~ring recommendations are made to optimize the safety aspects of <br />open pit mining in the Colowyo Mine area. <br /> <br />• <br />u <br />W.R.WRHIER Project 0807 III--3 <br />& ASSQCI~i~ <br />Pseudo-Static <br />