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<br />. <br /> <br />oaD9 <br /> <br />Woodward. Clyde Consultants <br /> <br />. <br /> <br />V. STABILITY OF UPSTREAM SLOPE <br /> <br />The test hole logs and laboratory tests show that the <br /> <br />materials in proposed Zone 2 borrow areas X, X-Wand X-SW are <br /> <br />. <br /> <br />generally layered, consisting largely of silty sands (SM) with <br /> <br />lesser amounts of sands and gravelly sands (SP and SW). In our <br /> <br />opinion, when these materials are excavated in the borrow <br /> <br />. <br /> <br />areas, the resulting mixtures in the embankment will generally <br /> <br />be impervious (about 1 foot/year). We believe that the low <br /> <br />permeability and low cohesion material presently contemplated <br /> <br />. <br /> <br />from these borrow areas may not provide a stable upstream <br /> <br />slope, even ~nder modest drawdown conditions, and that some <br /> <br />slumping may occur. <br /> <br />. <br /> <br />We recommend the upstream slope be redesigned for rapid <br /> <br />drawdown conditions giving full consideration to the type of <br /> <br />materials which can be developed from the above "X" borrow <br /> <br />. <br /> <br />areas, or other available borrow areas, under construction <br /> <br />excavation conditions. <br /> <br />The maximum section as shown on Figure 3 provides for 3 <br /> <br />. <br /> <br />feet of riprap on 1-1/2 feet of bedding materials. We believe <br /> <br />that this is a conservative design for upstream slope <br /> <br />protection at this location, providing properly sized rock and <br /> <br />. <br /> <br />bedding materials are used. We understand that consideration <br /> <br />is being given to the use of soil-cement upstream slope <br /> <br />. protection in lieu of the rock riprap because of the long haul <br /> <br />. <br /> <br />that would be required for the rock. Soils which would be <br /> <br />- 20 - <br /> <br />. <br /> <br />I!IDt. <br />.. <br />