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<br />II <br />~ <br />I <br />I <br />I <br />il <br />I <br />fl <br />~ <br />t <br />II <br />II <br />II <br />II <br />:1 <br />I <br />I <br />I <br />J <br /> <br />Simons, Li and Associates, Inc. <br />Job. No. 6143J002 <br />Project: Portland Flume Reconstruction <br /> <br />Special bedding material is not required for either the channel <br />or box culverts due to the granular nature of the subsoils. <br />However, due to the variable maximum particle size, it may be <br />necessary to overexcavate along much of the alignment to remove <br />projections of large cobbles and boulders or bedrock into the <br />excavations. The following procedure is recommended for prep- <br />aration of excavations: <br /> <br />1. Remove the existing concrete lining and excavate to <br />the required elevation. In areas where overexcavation <br />due to rock projection is not required, densify any <br />loose or disturbed soils in the bottom of the excava- <br />tion by surface compaction. Some type of vibratory <br />compaction will probably be most effective. <br /> <br />2. In areas requiring overexcavation, place and compact <br />backfill to finished subgrade levels. On-site soils <br />may by used for backfill provided all organics and <br />material over 6 inches in size is removed prior to <br />use. Compacted lift thickness should be limited to 8 <br />inches. Nesting of larger rock should be avoided. <br /> <br />3. All backfill and loose or disturbed subgrade should be <br />compacted to a minimum of 95 percent of the maximum <br />dry density as determined in accordance with ASTM D698 <br />or 70 percent relative density as determined in accor- <br />dance with ASTM D 2049. Backfill should be placed and <br />compacted within a moisture range of 3 percent below <br />to 3 percent above optimum. <br /> <br />-5- <br />