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City of Plymouth
STANDARD SPECIFICATIONSTABLE OF CONTENTS

WW.211 SPECIFICATIONS FOR BACKFILL - WASTEWATER

  1. DESCRIPTION
    1. All trenches or excavations shall be backfilled to the original surface of the ground or such other grades as shown or directed. In general, the backfilling shall be carried along as speedily as possible and as soon as the concrete, mortar, and/or other masonry work and pipe joints have sufficient strength to resist the imposed load without damage.

  2. GENERAL
    1. Do not completely backfill trenches until required pressure and leakage test have been performed, and until the utilities systems as installed conform to the requirements specified in the pertinent Sections of these Specifications.
    2. Do not allow or cause any Work performed or installed to be covered up or enclosed by work of this Section prior to required inspection, tests, and approvals.
    3. Should any or the Work be so enclosed or covered up before it has been approved, uncover all such Work and, after approvals have been made, refill and compact as specified, all at no additional cost to the Owner.
    4. Backfill excavations as promptly as progress of the work permits, but not until completion of the following:
      1. Inspection, testing, and approving of underground utilities.
      2. Approval of existing compaction.
      3. Removal of debris.

  3. MATERIALS
    1. The following materials shall be used to backfill the trenches in accordance with and in the manner indicated by the requirements specified herein:
      Class IAngular, 1/4 to 1 1/2 inch (6 to 40 mm), graded stone such as crushed stone.
      Class IICoarse sands and gravels with maximum particle size of 1 1/2 inch (40 mm), including variously graded sands and gravels containing small percentages of fines, generally granular and non-cohesive, either wet or dry. Soil types GW, GP, SW, and SP are included in this class.
      Class IIIFine sand and clayey gravels, including fine sands, sand-clay mixtures, and gravel-clay mixtures. Soil types GM, GC, SM, and SC are included in the class.
      Class IVSilt, silty clays, and clays, including inorganic clays and silts of medium to high plasticity and liquid limits. Soil types ML, MH, CH, and CL are included in this class. These materials are not recommended for bedding and are only to be used when permitted by the City Representative. This class shall also include any excavated material free from rock (3 inches and larger), concrete, roots, stumps, rubbish, frozen material, and other similar articles whose presence in the backfill would cause excessive settlement.

  4. BEDDING, HAUNCHING, AND INITIAL BACKFILL
    1. Bedding materials under the pipe and haunching materials to the springline of the pipe shall be #8 stone unless another material is agreed upon prior to construction by the City Representative and the Contractor [Design Standard WW-3]. No significant deviation from this material will be permitted for use without authorization from the City Representative.
    2. The bedding shall have a depth below the pipe of one-fourth (1/4) the outside pipe diameter below the pipe.
    3. Initial backfill from the springline of the pipe to 12" above the pipe shall be Class I or II material as described above.
    4. All material shall be placed in the trench in approximately six (6) inch layers. Each layer, before compaction shall be leveled and evenly distributed on both sides of the sewer so as not to disturb, displace, of damage the sewer and shall be thoroughly compacted.

  5. METHOD A - FINAL BACKFILL IN AREAS NOT SUBJECT TO VEHICULAR TRAFFIC
    1. The trench between a level twelve (12) inches above the top of the sewer and 6" below the finished grade shall be backfilled with Class I, II, or III materials, as described above, deposited with mechanical equipment in such a manner that will "flow" onto the bedding and free-fall. The Contractor shall consolidate the backfill by the back and forth travel of a suitable roller, wheeled device or other similar heavy equipment until no further settlement is obtained. Heavy equipment shall not be used until there is a cover of not less than three (3) feet over the sewers.
    2. The top six (6) inch depth shall be filled with good top soil and seeded in accordance with these specifications. Existing top soil and sod may be used if properly separated and preserved. In the event of any question regarding the susceptibility of an area to traffic, the City Representative's decision will govern.
      To assist in promoting maximum settlement, the surface of the trench shall be left in a slightly rounded condition. Periodic dressing of the backfill in the trench to promote drainage and safety conditions shall be made during the course of the contract as required or ordered by the City Representative.
    3. During construction, no ground water, dirt, mud, gravel, etc. shall be allowed to enter the newly constructed conduits or structures or existing parts of the collection system.

  6. METHOD B - FINAL BACKFILL IN AREAS SUBJECT TO VEHICULAR TRAFFIC
    1. The trench between a level of twelve (12) inches above the top of the sewer and twelve (12) inches below grade, shall be backfilled with Class I or II materials, deposited in uniform layers of six (6) inches. Each layer shall be thoroughly compacted by mechanical tamping utilizing a crane mounted hydraulic vibratory compactor or jumping jack type compactor. Each layer shall be placed. This procedure shall be followed if in the opinion of the City Representative, the trench walls remain stable during compaction. The City Representative may authorize the Contractor to push from the back of the trench the Class I or II material into the trench the full depth, not to exceed twenty (20) linear feet horizontally along the trench bottom and compact using the vibratory compactor in six (6) inch lifts.
    2. Crane mounted vibratory compactors shall be capable of producing 1900 cycles per minute and have a compaction plate with minimum dimensions of twenty-three (23) inches by thirty-one (31) inches. The compactor shall be similar to those as manufactured by Allied or HoPac.
    3. Jumping jack compactors shall have a compaction plate with maximum dimension of twelve (12) inches by twelve (12) inches. Manufacturer recommendation shall be supplied for verification.
    4. When Class I or II materials do not contain sufficient moisture to obtain proper compaction in the opinion of the City Representative, the materials shall be moistened or wetted as directed by the City Representative.
    5. The surface of the trench shall be left twelve (12) inches below finish grade if the surface is subject to traffic. This twelve (12) inch depth shall be filled with two (2) six (6) inch layers of compacted #53 limestone base material, shaped, graded, and compacted. In either case, the Contractor shall maintain the surface until the permanent pavement is placed.
    6. The compacted aggregate base materials shall conform with the Indiana State Highway Department Standard Specification, latest edition, for Compacted Aggregate Base. In the event that suitable granular material capable of compaction of obtainable from the trench excavations and can be satisfactorily segregated, then upon approval of the City Representative, the material may be used for the top layer of compacted base over the surface of the backfill in lieu of the specified Compacted Aggregate Base material. Density testing of the above backfilled trenches shall be performed by an approved commercial testing laboratory. All backfill placed under Method B shall be tested in accordance with AASHTO-T-99.
    7. Density testing shall be performed immediately prior to permanent pavement replacement and after the upper three (3) to five (5) inches of the compacted aggregate base or temporary pavement is removed to allow paving. When backfill has been placed using vibratory compaction, testing shall be made at the exposed surface every four hundred (400) feet. All test locations shall be determined by the City Representative. In the event that the density test results show a compaction of less than one hundred (100) percent Standard Proctor Density AASHTO T-99, the area(s) represented by such test(s) shall be immediately re-compacted using Method C. Paving shall not proceed until all areas to be paved have met the density requirements.

  7. BACKFILLING AROUND STRUCTURES
    1. The backfill around manhole structures other than pipes shall be made with Class I or II materials, shall be done in a manner to prevent after-settlement, shall be tamped/compacted in a satisfactory manner and shall be left at the proper grade with a smooth even surface. If the required excavation for any new structure has been carried below the level of any existing or new pipe lines or conduits which are located within the limits of the excavation, the Contractor shall take special precautions in compacting the backfill as it is placed beneath the level of the pipes or shall provide compacted granular fill or suitable pipe supports to prevent any damaging stress or strain to the pipe due to earth backfill and superimposed live loads.

  8. MAINTAINING TRENCH SURFACES
    1. TAll surface settlement of the backfill along trenches located beneath streets, roads, alleys, driveways, and parking lots which are subject to traffic shall be kept filled level with or slightly above the original paved surface at all times with compacted aggregate base material until the permanent pavement is satisfactorily restored. Special attention shall be given by the Contractor to timely and proper maintenance, leveling, and grading of the surface of all backfilled trenches. The surface of streets, roads and alleys shall be maintained smooth and free of ruts and water trapping depressions by periodic power blaming, scarifying and/or filling settled areas, ruts, pockets, and holes with compacted aggregate base material.
    2. As a dust preventative, the Contractor shall apply, at his expense, calcium chloride over the surface of the compacted aggregate base in such amounts and at such times as are necessary to avoid or eliminate dust complaints. In the event of any questions regarding the existence of a dust nuisance, the City Representative's decision on the matter will govern. The material used shall be Regular Flake Calcium Chloride having a minimum chemical content of 77% Calcium Chloride. Unless otherwise ordered by the City Representative, the rate of application shall be three (3) pounds per square yard of surface covered.
    3. Wherever surface settlement is not critical, the backfill shall be neatly rounded over the trench to a sufficient height to allow for settlement to grade after consolidation unless otherwise specified or ordered by the City Representative. Prior to completion of all work under this contract, any surface settlement below original ground surface shall be refilled in a satisfactory manner and reseeded as specified is required.

  9. RESTORATION OF SURFACES
    1. All surfaces shall be restored to original condition or better. This includes, but is not limited to, asphalt roads, drives, concrete curbs, sidewalks, driveways, and lawns.
    2. All surfaces must be saw cut in a neat straight line prior to construction and if damaged during construction, surface will be re-cut to form a neat straight line.
    3. Grass areas must be graded, cleaned of rock and other debris, seeded with a good quality seed, and mulched.

END OF SECTION TABLE OF CONTENTS



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