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120 -8 . 1 . 4 Use of A-7 Material : In the backfilling of trenches , A- 7 material may be used from a point 12 inches above the top of the pipe up to the elevation shown on the FDOT Design Standards as the elevation for undercutting of A- 7 material . 120 -8 . 1 . 5 Time of Placing Backfill : Do not place backfill against any masonry or concrete abutment , wingwall , or culvert until the Engineer has given permission to do so , and in no case until the masonry or concrete has been in place seven days or until the specified 28 -day compressive strength occurs . 120 -8 . 1 . 6 Placement and Compaction : Place the material in horizontal layers not exceeding 6 inches compacted thickness , in depth above water level , behind abutments , wingwalls and end bents or end rest piers , and around box culverts and all structures including pipe culverts . When the backfill material is deposited in water , compact per 120 - 8 . 2 . 5 and 120 -8 . 3 . 4 . The Contractor may elect to place material in thicker lifts of no more than 12 inches compacted thickness outside the soil envelope if he can demonstrate with a successful test section that density can be achieved . Notify the Engineer prior to beginning construction of a test section . Construct a test section of 500 feet in length . Perform five tests at random locations within the test section . All five tests must meet the density required by 120 - 7 . 2 . Identify the test section with the compaction effort and soil classification in the Agency Logbook . In case of a change in compaction effort or soil classification , construct a new test section . When a test fails the requirements of 120 -7 . 2 , construct a new test section . The Contractor may elect to place material in 6 inches compacted thickness at any time . 120 -8 . 2 Additional Requirements for Structures Other than Pipe : 120 -8 . 2 . 1 Density : Where the backfill material is deposited in water, obtain a 12 inch layer of comparatively dry material , thoroughly compacted by tamping , before verifying the layer and density requirements . Meet the requirements of the density Acceptance Criteria . 120 -8 . 2 . 2 Box Culverts : For box culverts over which pavement is to be constructed , compact around the structure to an elevation not less than 12 inches above the top of the structure , using rapid -striking mechanical tampers . 120 -8 . 2 . 3 Other Limited Areas % Compact in other limited areas using mechanical tampers or approved hand tampers , until the cover over the structure is at least 12 inches thick . When hand tampers are used , deposit the materials in layers not more than 4 inches thick using hand tampers suitable for this purpose with a face area of not more than 100 int . Take special precautions to prevent any wedging action against the masonry , and step or terrace the slope bounding the excavation for abutments and wingwalls if required by the Engineer . 120 -8 . 2 . 4 Culverts and Piers : Backfill around culverts and piers on both sides simultaneously to approximately the same elevation . 120 -8 . 2 . 5 Compaction Under Wet Conditions : Where wet conditions do not permit the use of mechanical tampers , compact using hand tampers . Use only A- 3 material for the hand tamped portions of the backfill . When the backfill has reached an elevation and condition such as to make the use of the mechanical tampers practical , perform mechanical tamping in such manner and to such extent as to transfer the compaction force into the sections previously tamped by hand . 120 -8 . 3 Additional Requirements for Pipe 15 Inches Inside Diameter or Greater : 120 -8 . 3 . 1 General : Trenches for pipe may have up to four zones that must be backfilled . 27 Technical Specifications F :\Public Works\ENGINEERING DIVISION PROJECTS\0744-8th St- US1 to 6th Ave\Admim\bid documents\0744 CONTRACT DOCUMENTS\Technical Specifications . doc