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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />founded on approximately 15 feet of soft, silty sand wi th 1 esser amounts of <br />gravel. The top of this zone was marked by a 6-inch layer of dark brown to <br />black, soft, organic material. Below this layer, dense silty sand with <br />gravel, cobbles, and a higher concentration of boulders was encountered. <br />Bedrock was not detected in any of the borings. <br /> <br />Soil sampl i ng for 1 aboratory testi ng was attempted usi ng a standard spl it <br />spoon sampler with and without Ca1 ifornia 1 iners, and Shelby tubes. Recovery <br />was often limited because of the presence of gravel and cobbles. When <br />successfully retrieved, California liner samples were used to determine <br />in-situ densities for the three different material zones. No laboratory shear <br />strength testing was performed, as recovery was also limited in the Shelby <br />tubes. <br /> <br />Shear strength parameters were derived considering particle size distribution, <br />density, and plasticity characteristics of the materials. Using the Bureau of <br />Recl amati on I s tabl e of "Average Engi neeri ng Soi 1 Properti es" and past <br />experience with similar soils, shear strength properties were assigned as <br />shown on Figure V.3. <br /> <br />2.4.4 <br /> <br />Fail ure Surface <br /> <br />There are two common failure surface configurations used for stability <br />analysis. A circular arc failure surface is more applicable for analyzing <br />essenti ally homogeneous or zoned embankments, founded on bedrock or thi ck <br />deposits of fine-grained materials. A non-circular failure surface, described <br />by linear segments, is generally more applicable for zoned embankments on <br />foundati ons contai ni ng one or several hori zontal or nearly hori zonta 1 weak <br />layers. Non-circular failure surfaces can also be used for relatively <br />homogeneous dams, which contain continuous well-defined horizontal weak <br />1 ayers. Both types of potenti a1 fai 1 ure surfaces were exami ned for Barnes <br />Meadow to determine the most critical configuration. The failure surfaces <br />shown on Figure V.3 are critical slip planes located by a search routine in <br />the computer program "PCSTABL5". <br /> <br />1231 H <br /> <br />-59- <br />