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<br />Woodward.Clyde Consuhants <br /> <br />U" P t'.< <br />~~l:l <br /> <br />the general right abutment foundation area (Ref.2). The <br /> <br />estimated range of low plasticity foundation soils is shown on <br /> <br />the Density vs. Liquid Limit chart, Figure 9. A significant <br /> <br />portion of the range falls within an area of soils sensitive to <br /> <br />soil structure collapse when saturated. Due to the low density <br /> <br />condition of the aeloian and alluvial soils overlying the <br /> <br />. <br /> <br />Pierre formation in the dam foundation considerable settlement <br /> <br />of the foundation can be anticipated from the weight of the dam <br /> <br />and future saturation. Thus, we believe that there could be <br /> <br />some risk of embankment cracking. We recommend the Bureau give <br /> <br />consideration to this risk in their embankment design as well <br /> <br />as possible foundation treatment. For instance, it will <br /> <br />probably be advantageous to place the embankment materials at <br /> <br />"optimum" to "optimum plus" moisture contents to provide <br /> <br />greater plasticity. <br /> <br />, <br /> <br />In our judgement, these low density conditions will result <br /> <br />in a rather low saturated cohesion value. es. The permeability <br />of this material is quite high. Vertical and horizontal <br /> <br />permeability values estimated from field tests for the Bureau's <br /> <br />seepage analysis are shown on Figure 7 (Bureau's drawing No. <br /> <br />553-PEL-68j. The strength and other physical parameters we <br /> <br />selected are given in Table 2. <br /> <br />- 15 - <br /> <br />(j <br />