Specifications for General Backfill

G.211 SPECIFICATIONS FOR GENERAL BACKFILL

  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, masonry and/or other work have sufficient strength to resist the imposed load without damage.
    2. For bedding and backfill of Storm and Sanitary Sewers see applicable provisions of Section WW.211.
    3. Water main pipe bedding and backfill shall meet the provisions of this Section.
  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 I Angular, 1/4 to 1 1/2 inch (6 to 40 mm), graded stone such as crushed stone.
      Class II Coarse 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 III Fine 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 IV Silt, 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. All rigid and flexible conduits shall be laid to the lines and grades shown on the plans, unless otherwise directed by the City Representative.
    2. Materials for bedding, haunching and intitial backfill under, around, and over the conduit or cable shall be Class II or compacted Class I material, as described above, and placed on a flat trench bottom. This material shall have a minimum thickness of four (4) inches below the conduit and shall extend six (6) inches over the top of conduit, or cable barrel at the sides.
    3. 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 conduit so as not to disturb, displace or damage the conduit and shall be thoroughly compacted. When Class I material is used, compaction may be accomplished by hand or mechanical tamping.
    4. Trenches twelve (12) inches in depth or less shall be filled with #53 limestone up to the original road surface for temporary road surface until paving can take place. Limestone shall be placed in six (6) inch layers compacted with a mechanical tamper.
  5. METHOD A - FINAL BACKFILL IN AREAS NOT SUBJECT TO VEHICULAR TRAFFIC
    1. The trench between a level six (6) inches above the top of the conduit cable or pipe and six (6) inches below grade shall be backfilled with Class I, II, III, or IV 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 conduit, cable or pipe. 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.
    2. The top six (6) inches shall be filled with good top soil and seeded in accordance with section S.250 of 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.
    3. During construction, no ground water, dirt, mud, gravel, etc. shall be allowed to enter the newly constructed conduits or structures or existing facilities.
  6. METHOD B - FINAL BACKFILL IN AREAS SUBJECT TO VEHICULAR TRAFFIC - MECHANICAL COMPACTION
    1. The trench between a level of six (6) inches above the top of the conduit or structure and twelve (12) inches below grade, subject to or possibly subject to vehicular traffic, shall be backfilled with Class I or II materials, deposited in uniform layers of twelve (12) inches. Each layer shall be thoroughly compacted by the use of mechanical tamping compaction to 95% of Standard Proctor. The upper most twelve (12) inches shall be compacted to 100% Standard Proctor.
    2. 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.
    3. 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 (INDOT) limestone base material, shaped, graded, and compacted. In any case, the Contractor shall maintain the surface until the permanent pavement is placed.
    4. The compacted aggregate base materials (#53) 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 is 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.
    5. Density testing of the above backfilled trenches shall be performed by an approved commercial testing laboratory or City personnel. Backfill placed under Method B shall be tested in accordance with AASHTO-T-99. 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. Paving shall not proceed until all Areas to be paved have met the density requirements.
  7. BACKFILLING AROUND STRUCTURES
    1. The backfill around 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. All 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