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• the Svendrup-Munk formula and arun-up factor of 2.0(3). Settlement was analyzed by <br />determining the change in stress from original stratum pressures to final pressures once <br />the embankment is built. The change in void ratione was determined to be 0.08 from a <br />standard stress/void ratio curve.(3) The total required freeboard is 3.04 feet, which <br />makes the designed freeboard (3.15 feet) acceptable. <br />The summation of volume requirements, spillway flowline, embankment settlement <br />and wave run-up puts the crest of the dam at an elevation of 7,459', thirty-one feet above <br />the upstream toe. <br />Embankment stability was analyzed by the method of slices for various slip circles. <br />Slopes of 3H:1V upstream and 254:1 downstream were chosen using USBR recommendations <br />for SC type soil.(2) Normal and tangential forces were calculated for each slice with pore <br />pressures being determined by overlaying the pond profile on the embankment flow net. <br />Flownets were drawn for full reservoir, rapid drawdown, end-of-construction and rainfall <br />states with the phreatic lines determined by Casagrandes' graphical method (5) <br />• <br />Slip Circle No. 1 represents toe failure on the upstream slope. Calculation sheets 12 <br />through l4 show the factor of safety for the circle under full reservoir, rapid drawdown <br />and end-0f-construction conditions. Slip Circle No. 2 is base failure on the upstream slope <br />with stability being analyzed for the three pore pressure conditions along with a 1,250 <br />pound surcharge load on the dam crest. Slip Circles No. 3 and No. 4 are toe and base <br />failure on the downstream slope. These surfaces were analyzed during rainfall conditions <br />only. This is the condition that results in the maximum pore pressure, therefore, the least <br />stability. The critical circle appears to be the downstream slope during a rainfall <br />condition with failure occuring at the base. The factor of safety is 1.52, however, which <br />is sufficient. <br />Calculation sheets 19 and 20 show the factor of safety for the embankment under <br />seismic loading conditions. The New Elk Mine lies within zone 1 on the seismic zone map <br />which represents a 0.05 seismic coefficient. The least factor of safety appears to be 1.41 <br />on the downstream slope under seismic loading and rainfall conditions. <br />• Anti-seep collars will be placed every 20 feet on the 24 inch Q CMP principal <br />spillway. The collars, along with proper compaction, will preclude any piping along the <br />-2- <br />