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<br />. <br /> <br />Woodward.Clyde Consultants <br /> <br />'. .. <br />" - <br /> <br />oJ I..J <br /> <br />. <br /> <br />existance of weak layers and swelling materials should be <br /> <br />thoroughly investigated. <br /> <br />The density parameter for the pierre formation for our <br /> <br />. <br /> <br />stability analyses was based on density data determined by the <br /> <br />Bureau of Denison samples obtained from the above drill hole <br /> <br />. <br /> <br />(Ref. 14). Based on our replot of all of the direct shear data <br /> <br /> <br />(Ref. 14) for the residual strengths of the Denison siltstone <br /> <br />(CL) cores tested by the Bureau and considering the triaxial <br /> <br />shear test results on the CH soil from the test hole at the <br /> <br />. <br /> <br />railroad bridge relocation location (Ref. 10), we selected the <br /> <br />shear strength parameters given in Table 2. We do not know if <br /> <br />. <br /> <br />an effort was made to orient apparent weak laminations in the <br /> <br /> <br />formation with respect to the failure plane selected in the <br /> <br />direct shear tests. From the average results of density, water <br /> <br />, <br /> <br />content and specific gravity for the above samples, it is <br /> <br /> <br />indicated that the pierre formation samples were saturated in <br /> <br />their natural state. <br /> <br />Consideration of the strength factors for the Pierre <br /> <br />I <br /> <br />formation materials was largely based on laboratory tests on <br /> <br />samples from the one Denison sample hole recently drilled. We <br /> <br />. <br /> <br />recommend that a detailed investigation be made over the broad <br /> <br /> <br />area and if any weak layers are found in the formation they be <br /> <br />pinpointed and examined. In addition, the swelling potential <br /> <br />at structure sites should be studied in detail. We have some <br /> <br />I <br /> <br />concern that excessive erosion could occur on an unprotected <br /> <br />- 17 - <br /> <br />fj <br />