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<br />5.7 Investigate the use of the upstream alluvial materials <br />on the south bank for use in the core. It is possible that <br />sufficient volumes of silty clay and clayey silt can be found <br />having less plasticity than the alluvial clays on the north bank. <br /> <br />. <br /> <br />5.8 The soundness of the Pierre Formation and its reaction <br />to saturation should be investigated by test trenches on the <br />left abutment. Large scale field saturation by ponding or labor- <br />atory testing of selected samples would be appropriate to deter- <br />mine the possible slaking of the Pierre. Test trenches provide <br />a better picture of the continuity of the material and possible <br />fractures. <br /> <br />. <br /> <br />5.9 The slaking or softening of the exposed Pierre in the <br />unlined intake channel of the service spillway should be in- <br />vestigated. It will be subjected to alternate wetting and <br />drying, which are unfavorable to those soft rocks that are <br />likely to contain inclusions of plastic clay such as the Pierre, <br />but with sufficient silty zone to permit rapid moisture fluctu- <br />ations. <br /> <br />5.10 ponding tests should be made of the surficial deposits <br />on the left bank above the Pierre Formation to determine a <br />possibility of softening and collapse beneath the embankment. <br /> <br />5.11 Collapse tests should be undertaken of the silty and <br />sandy materials on the south or right bank foundation to deter- <br />mine the possibility of subsidence upon an inundation period. <br />Field ponding tests of shallow materials and laboratory tests <br />for deeper materials are appropriate. <br /> <br />5.12 Gravelly materials for Slurry trench construction and <br />for filters do not appear to be locally available. Possibly <br />electrical resistivity profiles or additional borings will dis- <br />close areas in which the deep gravelly formations of the south <br />side near Bijou Creek are within the reach of gravel pit exca- <br />vation. <br /> <br />5.13 The flood problem of Bijou Creek is not controlled by <br />the Narrows Dam. The close proximity of the south end of the <br />Narrows Dam to Bijou Reservoir and Creek should make it easy <br />to bypass Bijou Creek or at least flood flows into the Narrows <br />Dam pool. Any deep excavation necessary might explore gravel <br />useful for Slurry-wall construction and filters. <br /> <br />. <br /> <br />6.0 Design Safety <br /> <br />. <br /> <br />Based on the data available and on the feasibility analyses <br />and the preliminary design that have been prepared, it is my <br />professional opinion that a safe dam can be designed and con- <br /> <br />8 <br />