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<br />It must be demonstrated that the long-term slope safety factor (which is the ratio of resisting <br />forces to driving forces) be 1.5 or higher for the embankment. Since the material will have <br />almost no cohesion, the slope stability can be analyzed in a relatively simple way. Assuming a <br />cohesionless soil (conservative), the factor of safety is equal to: <br />FS =Tan ~ <br />Tan I <br />where: <br />~ =internal angle of friction <br />1=actual slope angle <br />At a slope of 4H:1 V,1= 14.0 degrees. Using an internal angle of friction of 36.0 degrees, this <br />results in a factor of safety of 2.57. To fall below a safety factor of 1.5, the angle of friction <br />would have to be lower than 21 degrees, which is impossible in a jagged, angular, rocky material <br />of this type. <br />• In my experience collecting samples, conducting laboratory tests and computer analyses of many <br />slopes throughout Colorado, I believe this is a reasonable estimate for the slope safety factor on <br />this site. This is primarily due to the very mild slope of 4H:1 V and the high friction angle of the <br />material. The relatively low slope height of approximately 70 feet also lessens the chances of a <br />failure. <br />The expected dry density range of the material is from 110 to 130 pounds per cubic foot, which <br />depends on the type of material loaded from the mine and how it was mined or delivered to the <br />mine belt. <br />Moisture in the slope is also an important consideration in a slope stability analysis but only in <br />soils of higher cohesion. Cohesionless soils are not usually adversely affected by changes in <br />moisture content in the soil. Earthquake potential is also minimal in most of Colorado. <br /> <br />