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I I I I I I I I I I I I I I I I I I I Simons, Li and Associates. Inc. Job Number 6l43J002 Project Portland Flume Reconstruction Special bedding material is not required for either the channel or box culverts due to the granular nature of the subsoils, However, due to the variable maximum particle size, it may be necessary to over-excavate along much of the alignment to remove projections of large cobbles and boulders or bedrock into the excavations. The following procedure is recommended for preparation of excavations: 1. Remove the existing concrete lining and excavate to the required elevation, In areas where over-excavation due to rock projection is not required. densify any loose or disturbed soils in the bottom of the excavation by sur- face compaction. Some type of vibratory compaction will probably be most effective, 2. In areas requiring over-excavation, place and compact backfill to finished subgrade levels. On-site soils may be used for backfill provided all organics and material over 6 inches in size is removed prior to use, Compacted lift thickness should be limited to 8 inches, Nesting of larger rock should be avoided. 3. All backfill and loose or disturbed subgrade should be compacted to a minimum of 95 percent of the maximum dry density as determined in accordance with ASTM D698 or 70 percent relative density as determined in accordance with ASTM D2049. Backfill should be placed and compacted within a moisture range of 3 percent below to 3 percent above optimum. Recommendations for structural elements supported on compacted fills or prepared subgrade are dependent upon satisfactory site preparation and the placement and compaction of sUbsequent fill zones. Therefore. earthwork relative to structural support should be accomplished under observation and testing should also be pro- @ -5-