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801 DIVISION 800 STRUCTURES SECTION 801 ... 801 649 DIVISION 800 STRUCTURES SECTION 801 EXCAVATION AND BACKFILLING 801.01 Description. The work under this item shall include the removal

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  • 801



    SECTION 801

    EXCAVATION AND BACKFILLING 801.01 Description. The work under this item shall include the

    removal of material, of whatever nature, necessary for the construction of foundations for bridges, box culverts, and retaining walls according to the plans or as directed. It shall include the furnishing of necessary equipment and the construction of cofferdams, shoring, etc., which may be necessary for the execution of the work. It shall also include dewatering and the subsequent removal of cofferdams and shoring and the backfilling with suitable materials as herein specified. It shall also include the disposal of excavated material not required for backfill, in a manner and in locations as herein specified and/or as shown on the plans. Compliance with the applicable provisions of Section 110 is an essential requirement of work performed under this Section. Unless a specific pay item is provided in the Contract, work required to comply with Section 110 will not be paid for separately but will be considered subsidiary to other items of the work.

    801.02 Preservation of Channel. No excavation shall be made within stream channel limits outside a vertical plane 3' (1 m) from the footing lines and parallel thereto unless approved by the Engineer. Unless otherwise specified, no excavation shall be made outside of cofferdams, caissons, or shorings without the permission of the Engineer. If excavation or dredging is allowed at the site of the structure before cofferdams, caissons, or shorings are sunk or in place, the Contractor shall, at no cost to the Department, and after the foundation is in place, backfill such excavation to the original ground surface or stream bed elevation with gravel or crushed rock material satisfactory to the Engineer. Excavated material not used for backfill shall be disposed of according to Section 210.

    801.03 Depth of Footings. The elevation of the bottoms of footings, as shown on the plans, shall be considered as approximate only. The Engineer may require such changes in dimensions or elevations as may be necessary to secure a satisfactory foundation.

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    After each bridge footing in rock excavation has been completed to plan elevation, one hole 1½" (35 mm) or more in diameter shall be drilled to a minimum depth of 5' (1.5 m) for each 50 square feet (5 sq m) or less of bearing area. If the footing elevation is then lowered, the same pattern of such holes shall be drilled after the new excavation has been completed. No direct payment will be made for this drilling as it is considered a part of the items of excavation for structures.

    801.04 Preparation of Foundations. Foundations, where practicable, shall be constructed in open excavation and, where necessary, the excavated faces shall be sloped, shored, or protected by cofferdams according to approved methods.

    Rock or other hard foundation material shall be reasonably free of loose material. The foundation excavation shall be cleaned and cut to a firm surface, either leveled, stepped, or roughened, as directed by the Engineer. Seams shall be cleaned and filled with concrete, mortar, or grout. Excavation in rock shall be made to neat line of footings. When the use of explosives has been approved by the Engineer, care shall be exercised to avoid shattering rock faces by excessive blasting. The Contractor shall be responsible for any extra work and associated costs caused by excessive blasting.

    When concrete is to rest on an excavated surface other than rock, special care shall be taken not to disturb the bottom of the excavation. As a minimum, the final 1' (0.3 m) of excavation shall be completed by hand methods. The final removal of the foundation material to grade shall not be made until just before the concrete is to be placed. Foundation pits shall be kept dry and free of flowing water.

    Details for all excavation and/or shoring for foundation work adjacent to operated railroad tracks and plans of falsework, staging, protective sheeting, or other temporary construction near the operated track, shall be approved by the Railroad Company prior to beginning the work. The Contractor shall construct the work according to the approved plans.

    801.05 Cofferdams. (a) General. Cofferdams for foundation construction shall be safely designed and constructed, and made as watertight as is necessary for proper performance of the work. The interior dimensions of cofferdams shall provide sufficient clearance for dewatering, the construction of forms, and for inspection.

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    Cofferdams that are tilted or moved laterally shall be righted, reset, or enlarged as necessary. This shall be at no cost to the Department.

    When natural conditions are encountered that render it impracticable to dewater the foundation before placing concrete, the Engineer may require the construction of a concrete foundation seal of such dimensions as may be necessary, according to Subsection 802.11. The water shall then be pumped out and the balance of the concrete placed in the dry. During the placing of a foundation seal, the elevation of the water inside the cofferdam shall be controlled to prevent any flow through the seal.

    (b) Protection of Concrete. Cofferdams shall be constructed so as to protect the concrete against damage from a sudden rising of the stream and to prevent damage to the foundation by erosion. No bracing shall be left in cofferdams in such a way as to extend into the substructure concrete without the written permission of the Engineer.

    (c) Details Required. Details for each unit of cofferdam construction, complete with dimensions and kind and condition of materials, shall be submitted to the Engineer prior to construction, for informational and record purposes. These details shall be prepared and/or approved by a Registered Professional Engineer who shall certify that the adequacy of all components has been verified. File copies of all design calculations shall be maintained by the Contractor until final acceptance of the project. The Contractor shall be responsible for the results obtained by the use of the cofferdam design. Construction of the cofferdam shall be according to the details submitted to the Engineer for informational purposes.

    (d) Removal. Unless otherwise provided, the cofferdams, sheeting, and bracing shall be removed after the completion of the substructure. Care shall be taken not to damage the finished concrete.

    801.06 Dewatering Foundations. Pumping from the interior of any foundation enclosure shall be performed in such a manner as to prevent the movement of water through the fresh concrete. No pumping will be permitted during the placing of concrete unless it is performed from a suitable sump separated from the concrete work.

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    The pumping shall continue until the placement of the concrete is completed.

    801.07 Inspection. After each excavation is completed, the Contractor shall notify the Engineer. No concrete shall be placed until the Engineer has approved the depth of the excavation and the character of the foundation material.

    801.08 Backfill. Spaces outside the streambed excavated for and not occupied by abutments, piers, or other permanent work shall be backfilled and compacted to the general level of the surrounding ground. This work shall be performed immediately after completion of each unit of concrete work and after the forms have been removed and the concrete has reached its minimum required strength. Material used for backfill shall be of the same quality as that removed and shall be reasonably free from large or frozen lumps, wood, and other extraneous material.

    Piers located within the streambed need not be backfilled unless directed on the plans or as required by the Contractor's cofferdam removal procedure. Material for backfilling in the streambed shall be reasonably clean gravel or crushed rock.

    Backfill within the roadway embankment and immediately adjacent to bridge abutments, culverts, retaining walls, or other places inaccessible to rollers, shall be placed in approximately 6" (150 mm) horizontal layers, loose measurement, at near optimum moisture content, and compacted with mechanical equipment to 95% of the maximum density as determined by AASHTO T 99. The specified density will not be required immediately adjacent to wingwalls of box culverts. The backfill in front of such units shall be placed first to prevent the possibility of forward movement. Special precautions shall be taken to prevent any wedging action against the concrete, and the slope bounding the excavation for abutments and wingwalls shall be stepped or roughened to prevent wedge action. Jetting of the fill behind abutments and wingwalls will not be permitted. Backfill for box culverts shall be placed equally on both sides of the culvert in 6″ (150 mm) lifts, loose measurement, and compacted as required above.

    Fill placed around piers shall be deposited uniformly on all sides to approximately the same elevation.

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    No backfill shall be placed against abutments, retaining walls, or box culverts until the concrete has cured for at least 14 days or until test cylinders show that the minimum strength has been obtained.

    Backfilling of structural plate pipe and arches shall be according to Subsection 608.03(d).

    The Department will perform acceptance sampling and testing of compacted backfill material in accordance wit

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