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1. To provide a relatively pervious fill having good drainage. <br />characteristics. <br />2. To achieve a reasonably good mixture of all of the overburden <br />materials within the embankment by vertical, rather than horizontal, <br />mixing so as to minimize the likelihood of lenses or layered zones <br />of materials of different composition. <br />3. To produce an embankment capable of sustaining settlement without <br />cracking or formation of voids within the mass as a result of sub- <br />sidence of the foundation or consolidation of the embankment. <br />The placing of spoil by end dumping of trucks over the edge of the lifts provides <br />the best means of accomplishing all of the foregoing objectives. It provides a relatively <br />free-draining embankment and results in a desirable degree of vertical mixing of sub-soil <br />and other fines with the coarser fragments of shale and sandstone. Natural sorting of <br />materials in the dumping process combined with impact action associated with the high <br />lifts results in the largest and most competent rock fragments being placed in the base <br />of the fill resting on the pervious clinker and at the bottom of each lift. While truck <br />traffic across the top of each lift will tend to reduce the permeability of a relatively <br />thin zone at the top of the lift, extensive crop line drilling along Streeter Canyon re- <br />vealed extremely porous clinker areas of considerable depth on both abutments through <br />which percolating water moving laterally across zones of lesser permeability will readily <br />drain to lower levels. The drainage efficiency of these porous clinker zones is evidenced <br />by the fact that the small amount of water occasionally carried in the upper reaches of <br />Streeter Gulch following rainstorms seldom, if ever, produced visible flow at the mouth <br />of the creek where it enters Good Spring Creek. Serious water inflow problems were <br />encountered in the former underground Red Wing Coal Mine in clinker areas lying below <br />the bed of Streeter Gulch. <br />The ability of the embankment to accommodate a reasonable amount of consolida- <br />lion without rupturing or cracking is extremely important. The surface soils in the lower <br />reaches of Streeter Conyon will undergo some consolidation because of the sheer weight <br />3 <br />