Laserfiche WebLink
HAWKS NEST MINE <br />EAST AND WEST PORTAL <br />SLOPE STABILITY OF <br />ROAD CUT AND FILL SLOPES <br />FIELD STUDY <br />On February 8, 1984, Engineers Erom Mt. Highland Engineering and <br />Lambert and Associates, Geotechnical Engineering viewed the slopes <br />of the road cuts and fills at Western Slope Carbon's Hawks Idest <br />Mi~1e. Each slope caused by a road cut or fill was studied and the <br />"worst case" slope was determined based on evidence of failure, <br />steepness of slope, ability to obtain an undisturbed sample of the <br />cut and fill material typical to the area. The slope chosen and <br />sampled was a steep slope on the East Mine Tipple Road at cross <br />section 3+00. <br />LAB ANALYSIS <br />The soil sampled is typical of the area and is a Sandy Clay (SC) <br />with a natural dry density of 112 pcf. The results of the Triaxial <br />tests for the 3 samples are shown in the Appendix and show an <br />internal angle of friction of 20° and a cohesion of 1350 lbs/f t2 <br />at a 4$ strain. Recompaction end reforming o£ the soil increased <br />the cohesion above 1350 lbs/ft but was unmeasured and therefore <br />is a conservative estimate of the cohesion of the recompacted fill. <br />A similar sample in the parking lot slope taken two years ago showed <br />a cohesion of 2800 psf. <br />CALCULATIONS <br />Slope analysis was done by the Swedish method of circles which <br />assumes the failure plane to closely approximate a circular slip <br />surface. Calculations were made by the method of slices using a <br />computer program to successively approximate the failure plane of <br />the lowest factor of safety. <br />A "worst case" analysis was done for a 1008 slope to verify the <br />soils ability to conform to this slope without exceeding the <br />recommended safety factor of 1.5:1. The cut slopes were analyzed <br />with no overburden, fill slopes were analyzed with HS 20 wheel <br />loading on the road surface. <br />The results of this analysis are shown on the graph of the safety <br />factors and heights of slope. The graph shows a cut slope safety <br />factor of 7.5 for a 1008 slope 10 feet high to a safety factor of <br />2.9 for a 1008 slope at 40 feet high. The graph also shows a 100 <br />fill slope safety factor of 2.46 for 10 feet deep and a safety <br />factor of 2.12 for a 30 ft, deep fill. <br />