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Excavate and backfill for construction of bridges, box culverts, and other major structures.
Crusher Run Aggregate CR-6       901.01
Subfoundation Concrete       902.10, Mix No. 1
Sheet, shore, brace, and support all excavation contiguous to existing pavements and structures to prevent settlement, movement, or damage to the pavement or structure. Place excavated material in a manner to prevent damage to adjacent structures and incursion into waterways.
402.03.01 Backfill and Embankment Material. Use all suitable excavated material for backfill or store for future use. Do not waste excavated material without approval. Prior to using excavated material as backfill, remove boulders, logs, and other unsuitable material. Dispose of unsuitable material in an approved disposal area.
402.03.02 Footing Elevations. The elevations for the bottom of the footings specified in the Contract Documents are approximate only; the Engineer may direct changes in dimensions or elevations of footings to secure a satisfactory foundation during the period of construction.
402.03.03 Footing Foundations. Place footings on suitable foundations. Do not drive piles or place concrete until the foundations are approved.
Clean all rock and other hard foundation material of loose material and cut to a firm surface, either level or stepped, as directed. Clean out and grout all seams and crevices. Remove all loose and disintegrated rock and thin strata. When concrete will rest on an excavated surface other than rock, do not disturb the bottom of the excavation. Perform final removal of the foundation material to grade just prior to placement of reinforcement steel and concrete. When an item is included for Subfoundation Investigation (Section 419), use the item as directed to verify the character of the foundation.
Place faces of footings plumb against undisturbed material, rock, sheeting, shoring, or forms. Faces of footings in rock shall bear against a minimum 1 ft depth of rock. If the excavation will not stand plumb, install sheeting, shoring, or forms as required. When specified, sheeting used to construct spread footings shall be left in place and cut off as specified in 410.03.10. When not specified, or when sheeting is used to construct pile-supported foundations, the sheeting may be removed.
Design all required sheeting and shoring. When the material retained by the sheeting and shoring is greater than 6 ft high, submit the details, procedures, and computations the same as specified for falsework details in TC-4.01 and Section 499. The experience specified under TC-4.01 will be waived.
After removing the forms, backfill the void between the footing and the embankment with subfoundation concrete or tamped fill utilizing crusher run aggregate CR-6. Compact the material to a density of 92 percent of the maximum density as tested according to T 180, Method C. Use subfoundation concrete for backfill when footings are submerged. If the footings are below the water table, adjacent to railroad tracks, or more than 6 ft thick, submit footing form working drawings for approval.
Where foundation piles are used, excavate each pit to the as planned bottom of footing elevation before driving the piles. After driving is complete, remove loose and displaced material without damaging the piling. Leave a suitable bed to receive the footing concrete. For tremie seal, the displaced material may remain provided the minimum thickness of footing concrete, pile embedment, and the required sealing of the foundation seal is maintained.
Where foundation piles are not used on substructure units, other than box culverts, and excavation is required below the as planned bottom of the foundation, backfill the additional excavation with subfoundation concrete or lower the footing elevation and deepen the footing as directed. Provide a rough finish to rock foundations that are to receive footing concrete. For box culverts, backfill additional excavated spaces under the barrels with selected backfill.
402.03.04 Cofferdams and Foundation Seals. When cofferdams or foundation seals are required, submit working drawings and a complete description of the process as specified in Section 499. Timber or bracing left in the cofferdams or cribs shall not extend into the substructure concrete. Construct cofferdams in a manner that protects the concrete from damage.
(a) Foundation Seal. Refer to 420.03.05. When the foundation cannot be dewatered, the Engineer may require the construction of a concrete foundation seal. If a mud wave is created during the placement of the tremie seal, remove the displaced material to preserve the full foundation cross section specified. Then pump out the foundation and place the footing in the dry. When weighted cribs are employed and the crib’s weight is utilized to overcome a part of the hydrostatic pressure acting against the bottom of the foundation seal, provide special anchorage such as dowels or keys to transfer the entire weight of the crib into the foundation seal. When a foundation seal is placed under water, vent or port the cofferdam at low water level as directed.
(b) Pumping. Do not pump from the interior of the enclosure during the placing of concrete. Do not begin pumping from a sealed cofferdam until the seal has set sufficiently to withstand the hydrostatic pressure.
(c) Removal of Cofferdams or Cribs. Remove cofferdams or cribs after the completion of, and without damage to the substructure.
(d) Stability of Foundation. Stabilize the foundation area so that the concrete footing can be constructed in the dry.
402.03.05 Backfilling. Use suitable material for backfill. Continue backfilling to the surface of the surrounding ground or specified grade. Do not use Borrow until available project excavation is exhausted. Neatly grade the top surface of the backfilled areas. Compact as specified in Section 204 or Section 210.
Backfilling Against Structures. Backfill against various structures as follows:
(a) Brick Masonry. Backfill no earlier than seven days after completion of the section.
(b) Concrete Structures. Backfill when curing is completed and the concrete has achieved 80 percent of the specified compressive strength.
(c) Footings, Culverts, and Piers. Deposit fill on both sides to approximately the same elevation at the same time.
(d) Abutments, Retaining Walls, Culverts, or Other Structures. Place backfill in horizontal layers so that at all times there is a horizontal berm of uniformly compacted material behind the structure for a distance at least equal to the height of the abutment or wall remaining to be backfilled, except where undisturbed material protrudes into this area. Compact the berm as specified in 204.03. Jetting of fills or other hydraulic methods involving liquid or semiliquid pressure within the berm area are prohibited.
Class 3 Excavation will be measured and paid for at the Contract unit price per cubic yard for the volume of material actually removed from within the limits specified.
Excavation for pipe culverts, culvert end walls, inlets, and manholes is excluded from Class 3 Excavation.
Payment will be full compensation for all excavation, backfill, filling void around footings due to removing forms, blasting, grout, dewatering, removal and disposal of excess or unsuitable material, and for all material, labor, equipment, tools, and incidentals necessary to complete the work. When a Class 3 Excavation item is not included in the Contract Documents, the excavation will not be measured but the cost will be incidental to other pertinent items.
No measurement or payment will be made for removing any liquids.
Class 3 Excavation will extend a maximum of 18 in. to vertical planes outside of the structure. Where blasting is required, a maximum of 6 in. will be allowed below the planned elevation.
The upper limits on existing ground or embankments will be the existing groundline or the lower limit of roadway excavation. The lower limit of the two will control.
The upper limits on preliminary embankments will be the bottom of the as planned footing elevation. For stepped footings, the upper limits will be the bottom of the as planned footing elevation of the highest portion of the footing. If the preliminary embankment has a surcharge, the upper limits will be the lower limit of roadway excavation.
402.04.01 Additional excavation required below the elevation specified in the Contract Documents and necessitated by the lowering or deepening of footings, or the placing of subfoundations or underpinning, will be measured and paid for at the Contract unit price for Class 3 Excavation.
402.04.02 Sheeting, bracing, and shoring either removed or left in place, will not be measured but the cost will be incidental to other pertinent items unless otherwise specified.
402.04.03 Excavation necessary to expose or remove piles, grillages, sheeting, cribbing, masonry, or other obstructions will not be measured nor paid for if the excavation occurs outside the limits of excavation. Removal and disposal of obstructions within the limits of excavation will not be measured separately but the cost will be included in the Contract unit price for Class 3 Excavation.