Laserfiche WebLink
• <br />Introduction <br />C <br />The Cooley Gravel Company proposes to mine currently permitted property located near 104`h <br />Avenue and the South Platte River (see Location Map). The proposed mining operation will <br />extract gravel reserves from the property in some locations that aze adjacent to man-made <br />structures. It is desirable to maximize the extraction of the reserves as long as damage to these <br />structures is prevented. The rules and regulations of the Division of Minerals and Geology <br />requires that any mining within a 200 foot setback of aman-made structure show through <br />engineering analysis that the mining will not cause damage. The typical method of <br />demonstrating this is through a slope stability analysis. The information presented in this report <br />demonstrates that there aze adequate slope stability safety factors being maintained by mining to <br />with a setback ranging between 35 feet to 50 feet of the man-made structures, depending on the <br />assumed conditions. <br />The mining site is located in the floodplain of the South Platte River. Although the mining will <br />be done using dewateting and dry mining, the analysis in this study used worst case assumptions <br />based on the pit being excavated and then being flooded. The result would increase pore water <br />pressures in the exposed excavation and theoretically lower the safety factor. This analysis <br />assumed strength parameters for the soils in the azea based on past experience and accepted <br />values. No laboratory testing of the soils was done to verify the values. <br />Description of Structures <br />There aze several types of structures that mining would encroach closer than 200 feet. <br />The first is a series of powerline towers owned by the Public Service Company. The towers <br />almost bisect the property and run from east to west. <br />2. The second structure is the Fulton Ditch, which is located on the east side of the South Platte <br />River and runs to the North along the eastern perimeter of the mine site. The primary azea <br />where mining disturbance would encroach on the ditch is from the diversion structure north <br />approximately 2,800 feet towards 104`s Avenue. <br />3. Finally, mining along the property boundaries will pazallel public right-of--ways which may <br />have utilities and road improvements that lie within 200 feet of the mining azea. <br />Assumptions used in the Slope Stability Analysis <br />The mining methods around the structures would entail two sepazate and distinct approaches. <br />The mining azound the PSCo towers and adjacent to the right-of--way would be done in the dry <br />after a slurry wall has been installed around the perimeter of the property. The slurry wall <br />wou]d be located on the west side of the South Platte River and would be set back approximately <br />10 feet from the property line. The actual limits of mining would be setback an additional 25 <br />feet from the slurry wall to protect it. Once the slurry wall is completed, the mining operation <br />will then dewater the interior of the pit through well points, and begin the extraction of the gravel <br />reserves. <br />Page 1 <br />