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-14- <br />Method of Construction <br />The placement and compaction of the spoil will influence its overall <br />strength characteristics. Additionally, the permeability of the fill can be <br />significantly affected by the method of construction. We anticipate Colowyo <br />desires to construct the fill by hauling spoil rock from the active mine areas <br />to the disposal site with large mine trucks, probably in the range of 120 to <br />170-ton carrying capacity. We believe the fill should be placed in <br />approximately horizontal lifts. In order to maintain comparatively high <br />permeability within the fill, The use of thick lifts is desirable. lNe believe <br />lifts on the order of SO to 100 feet in range can be used because of the <br />insensitivity of the spoil site to settlement after construction. The previous <br />experience with the Streeter Canyon Fill has shown fills can perform <br />• satisfactorily with thick lifts for the planned purposes of open rangeland after <br />fi{{ construction. <br />Method of Analysis <br />The proposed spoil will be confined within an existing valley. Sheet 3 <br />and Fig. 3 illustrate representative spoil cross-sections. Our slope stability <br />analyses were performed using cross section A (Fig. I, Sheet I) which <br />represents, in our opinion, the critical area. We believe The placement of the <br />spoil within the valley will virtually eliminate risks of stability type problems <br />within The foundation soils on the east and west sides of The valley. The <br />planned 3:1 slope of the fill indicates a factor of safety of 2.1 to 2.4 for <br />infinite slope-type failure within the fill. <br /> <br />