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<br />Woodward.Clyde Consultants <br /> <br />, ~...~ <br />l.. (", d) <br />J""v\" <br /> <br />, <br /> <br />Field observations, recent flooding events and the <br /> <br />characteristics of the sandy, low plasticity, alluvial soils <br /> <br />indicate that these surficial soils are easily eroded and <br /> <br />transported. In our opinion, final design should consider the <br /> <br /> <br />direction and route the sediments will follow with respect to <br /> <br />the functioning of the appurtenant structures. <br /> <br />6. Pierre Formation <br /> <br />Logs of test holes along the proposed dam axis, Figure 2, <br /> <br />show the location and classification of the Pierre formation <br /> <br />materials. The formation materials have been generally <br /> <br />classified a siltstone. We have classified the materials as <br /> <br />clayey siltstone. The Pierre formation materials at this site <br /> <br />are generally less clayey than Pierre formation materials often <br /> <br /> <br />found at other locations. Some pierre formation materials are <br /> <br />fat clays (CH) and contain weak seams. We inspected a few <br /> <br />t <br /> <br />samples from one Denison continuous sample hole, 555-0-24, that <br /> <br />was recently drilled on the proposed dam axis. The results of <br /> <br />physical properties tests made on these samples are contained <br /> <br />. <br /> <br />in a Bureau Memorandum dated November 18, 1977 (Ref 14). Some <br /> <br />fat clays are in evidence in other exploration holes at the <br /> <br />site and fat clays (weathered shales) were reported in EM-217 <br /> <br />(Ref 4) at the emergency spillway location. This leads us to <br /> <br />conclude that some fat clays with low strength may be present <br /> <br />within the formation which might affect stability of the dam <br /> <br />and cause uplift of structures. In our opinion, the possible <br /> <br />- 16 - <br /> <br />II!Dt. <br />.. <br />