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<br />- 3- <br /> <br /> <br />parameters used in our analysis disregarded any cohesive strength in the <br />fill and the value of the angle of internal friction was assumed to be <br />37 degrees, as discussed on page 17 of our original report. The 37 degree <br />value for the angle of internal friction is a value which corresponds to <br />loose dumped fills and was based on observations at the current Energy <br />Fuels Mine. The compaction required by the current regulations for these <br />spoil disposal structures will result in a fill with considerably higher <br />internal strength than the values which were used in our analysis. There <br />is no method of establishing how high these values might be in the labora- <br />tory because of the size of materials involved in these structures. Ob- <br />servations of performance of rockfill as documented in the literature, in- <br />dicates that the compacted internal friction angles may correspond to <br />values ranging from 40 degrees to 60 degrees. The 37 degree value used in <br />our analysis was selected to allow for a worst case or residual shear <br />strength condition. <br />Page 4 of this memo dated January 2, 1980, Items 12, 13, and 14 were <br />essentially answered in our reply above regarding the surface drainage. <br />Regarding Item 12, we believe the long-term drainage and possible effects <br />on stability were considered in our Fig. 12 of the report dated September <br />11, 1979, presenting a summary of analysis of stability. This particular <br />analysis covers pile configuration IIA. A number of the various trial <br />failure surfaces were made. In this summary the water table was assumed <br />at different elevations in the spoil structure. and at the bedrock surface. <br />For each of these different elevations, a factor of safety was computed. <br />Trials 17 and 18 essentially assumed complete failure of all external and <br />internal drainage systems and total saturation of the spoil structure. The <br />water table was assumed to rise to elevation 7310 for analysis No. 17, and <br />to elevation 7410 in analysis No. 18. Both of these showed factors of <br />safety that were relatively low, but the chance of this saturation occurring <br />is remote. The permeability of the fill will be sufficiently high that the <br />risk of developing water tables at the elevations assumed for trials 17 <br />and 18 is remote. However, to allow MLRB to evaluate the effect of chang- <br />ing or failure of surface drainage facilities, we did evaluate this possi- <br />bility in our original submission. The lowest factor of safety computed <br />was for trial 18, which resulted in a factor of safety of 1.06, and this <br />analysis assumed that a free water surface extended to elevation 7410 with <br />all of the fill below that elevation completely saturated. This is not a <br />probable condition considering the internal rock drains required and the <br />planned surface drains. <br />Item 13 was agreed upon in the review by Energy Fuels and MLRB. <br />Item 14 has been previously answered. <br />Page 5 of this memo, dated January 2, 1980 - Item 15. Exhibit 9 in- <br />dicates a range of sizes for the toe buttresses. Figure 8 in our original <br />• <br />