SECTION_31_23_33_Backfilling_Trenches.docx
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SECTION 31 23 33 BACKFILLING TRENCHES
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SECTION 31 23 33
SECTION 31 23 33
BACKFILLING TRENCHES
| PART 1 | GENERAL |
| 1.1 | SECTION INCLUDES |
| A. | Trench backfill materials. |
| B. | Trench backfilling requirements. |
| C. | Surface restoration requirements. |
| 1.2 | DEFINITIONS |
| A. | Bedding: That surface of the Excavation or portion of the Pipe Zone below the pipe. |
| B. | Pipe Zone: That zone in a backfilling operation which supports, and surrounds the pipe barrel, and extends to 1 foot above the top of the pipe barrel. |
| 1.3 | SUBMITTALS |
| A. | Submit maximum laboratory dry density and optimum laboratory moisture content for: |
| 1. | Subgrade material, and |
| 2. | Each type of fill to be used. |
| B. | Upon ENGINEER's request, submit a written quality control Inspections and testing report describing source and field quality control activities performed by CONTRACTOR and its Suppliers. |
| 1.4 | QUALITY ASSURANCE |
| A. | Do not change material sources, or aggregate without COR’s knowledge. |
| B. | Reject backfill material that does not comply with requirements specified in this section. |
| 1.5 | STORAGE AND PROTECTION |
| A. | Storage: |
| 1. | Safely stockpile backfill materials. |
| 2. | Separate differing materials, prevent mixing, and maintain optimum moisture content of backfill materials. |
| B. | Protection: |
| 1. | During installation or repair, plug end of pipe or fitting except when installing next section of pipe or fitting. |
| 2. | Avoid displacement of and injury to Work while compacting or operating equipment. |
| 3. | Movement of construction machinery over Work at any stage of construction is solely at CONTRACTOR's risk. |
| 1.6 | SITE CONDITIONS |
| A. | Do not place, spread, or roll any backfill material over material that is damaged by water. Remove and replace damaged material at no additional cost to Government. |
| B. | Control traffic and erosion. Keep area free of trash and debris. Repair settled, eroded, and rutted areas. |
| C. | Reshape and compact damaged structural section to required density. |
| D. | Restore any damaged structure to its original strength and condition. |
| E. | Replace contaminated backfill at no additional cost to OWNER. |
| 1.7 | SEQUENCING |
| A. | Coordinate backfilling operation with pipeline commissioning requirements in Section 33 08 00. |
| 1.8 | ACCEPTANCE |
| A. | General: |
| 1. | Native material may be wasted as directed by COR if there is no additional cost to substitute material acceptable to COR. |
| 2. | For material acceptance refer to. |
| a. | Common fill, Section 31 05 13. |
| b. | Crushed aggregate base, Section 32 11 23. |
| c. | Cement treated fill, Section 31 05 15. |
| B. | Trench Backfilling: One test per Lot. |
Table 1: Lot Size for Trench Backfilling Operation
| Material |
| Lot Size |
| Subgrade (a) |
| 200 lineal feet |
| Common Fill (a) |
| 200 lineal feet per lift |
25 square feet of footing area per lift
| Crushed Aggregate Base (a) |
| 200 lineal feet per lift |
25 square feet of footing area per lift
| Flowable Fill |
| 50 cubic yards |
NOTES
(a) Proctor density, Section 31 23 26
(b) Compressive strength, Section 31 05 15
(c) Lift thickness above the pipe zone before compaction, 8 inches.
| 1.9 | WARRANTY |
| A. | Any settlement noted in Trench backfill or in structures built over the Trench backfill will be considered to be caused by improper compaction methods and shall be corrected at no cost to the Government. |
| B. | Restore structures damaged by settlement at no additional cost to Government. |
| PART 2 | PRODUCTS |
| 2.1 | BACKFILL MATERIALS |
| A. | Common fill, Section 31 05 13. |
| B. | Crushed aggregate base, Section 32 11 23. |
| C. | Cement treated fill, Section 31 05 15. |
| D. | Slag or asphalt bearing material not allowed. |
| 2.2 | ACCESSORIES |
| A. | Water: Make arrangements for sources of water during construction and make arrangements for delivery of water to site. Comply with local Laws and Regulations. |
| B. | Geotextile Fabric: Section 31 05 19. |
| C. | Identification Tape: Permanent, bright-colored, continuous-printed magnetic plastic tape, intended for direct-burial service; not less than 6 inches wide by 4 mils thick. The tape shall read "CAUTION: BURIED INSTALLATION BELOW". Color of tape as follows. |
| 1. | Red: Electric power lines, cables, conduit and lighting cables |
| 2. | Yellow: Gas, oil, steam, Petroleum or gaseous materials |
| 3. | Orange: Communications, alarm, signal, cables or conduits. |
| 4. | Blue: Potable water |
| 5. | Purple: Reclaimed Water, irrigation and slurry lines |
| 6. | Green: Sewer and storm drain lines |
| D. | Trace Wire: Contractor shall provide and install a trace wire within one foot of all new utilities placed underground, or as otherwise indicated. Trace wire shall be #14 insulated copper wire. Installation shall meet the following requirements: |
| 1. | If length of new utility is 500 feet or less the Contractor shall install one terminal box of 2 ½” diameter pipe at each end of the wire marking the utility location. |
| 2. | If length of new utility is greater than 500 feet, the Contractor shall place terminal boxes at 500 feet intervals. |
| 3. | Terminal boxes (Handley Industries or approved equal) shall have a metal screw-on type lid. |
| a. | The terminal box shall be encased in an 18” diameter by 12” deep concrete cylinder. |
| b. | The terminal box lid shall be flush with the top of the concrete cylinder and the top of the concrete cylinder shall be flush with adjacent pavement or 2” above the adjacent ground elevation. |
| 4. | The trace wire shall have a metal identification tag attached to the wire at each terminal box. The tag shall be engraved with the type of utility, and for pipelines the tag shall be engraved with the pipe size. |
| PART 3 | EXECUTION |
| 3.1 | PREPARATION |
| A. | Verify backfill material meets gradation requirements, foundation walls are braced to support surcharge forces imposed by backfilling operations, areas to be backfilled are free of debris, snow, ice or water, and Trench bottom is not frozen. |
| B. | If Subgrade is not readily compactable secure written authorization for extra excavation and backfill; Section 31 23 16. |
| C. | Avoid injuring and displacement of pipe and structures while compacting soil or operating equipment next to pipeline. |
| D. | Place geotextile fabrics; Section 31 05 19. |
| 3.2 | GENERAL BACKFILLING REQUIREMENTS |
| A. | Protect Subgrade from desiccation, flooding and freezing. |
| B. | Do not damage corrosion protection on pipe. |
| C. | Repair or replace damaged pipe at no additional cost to Government. |
| D. | Withdraw sheathing, Shoring, piles, and similar supports as backfilling progresses. Backfill and compact all holes left by removals. |
| E. | Provide sufficient water quality facilities to meet State water quality requirements. |
| F. | Water settling of Trench backfill is not permitted. "Jetting" of Trench backfill is prohibited. |
| 3.3 | PIPE ZONE |
| A. | Maintain uniform foundation along barrel of pipe with sufficient relief for joint connections. |
| B. | Use backfill materials meeting pipe manufacturer's recommendations. Maximum backfill particle size is 3/4 inch for plastic pipe. |
| C. | Do not permit free fall of backfill material which may damage pipe, pipe finish, or pipe alignment. |
| D. | Except where piping must remain exposed for tests, fill Pipe Zone as soon as possible. |
| 3.4 | TRENCH ABOVE PIPE ZONE. |
| A. | Maximum lift thickness before compaction is 8 inches. |
| B. | Fill unauthorized Excavations with material acceptable to COR at no additional cost to Government. |
| C. | Do not damage adjacent structures or service lines. |
| D. | Install continuous plastic line marker directly over buried lines 18 inches below finished grade. |
| 3.5 | MODIFIED BACKFILL LAYER METHOD |
| A. | At discretion of Contractor, backfill may be placed in thicker layers than indicated above subject to the following provisions. |
| 1. | Contractor proves the ability of proposed method to achieve specified average compaction density. |
| 2. | COR, on the basis of test results, approves the system in writing. |
| B. | Should Contractor find it necessary to change the method or any part of it, including the source of material, or the rate of placing the material, obtain approval of COR, who may require a further trial area. |
| C. | If testing shows a previously approved system is no longer producing the required degree of compaction, make changes to comply. |
| D. | Where vibration effects are creating environmental problems, make changes to eliminate problems. |
| 3.6 | COMPACTION |
| A. | Compact backfill, Section 31 23 26. |
| 1. | A-1 soils: 95 percent or greater of a Modified Proctor Density. |
| 2. | Other soils: 95 percent or greater of a Standard Proctor Density. |
| 3.7 | COMPRESSIVE STRENGTH |
| A. | Where a flowable fill is used, provide compressive strength indicated in Section 31 05 15. Use fill which flows easily and vibration is not required. |
| 3.8 | SURFACE RESTORATION |
| A. | Provide temporary paved surfaces where Trenches pass through roadways, Driveways or sidewalks. |
| B. | Restore paved surfaces. |
| C. | Finish landscaped surfaces with grass, Section 32 92 00 or with other ground cover, Section 32 93 13. |
| 3.9 | CLEANING |
| A. | Remove stockpiles from the site. Grade site surface to prevent free standing surface water. |
| B. | Leave borrow areas clean and neat. |
END OF SECTION
BACKFILLING TRENCHES Page 1
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