420 Page 287420 STRUCTURE EXCAVATION
420.1DESCRIPTION
This work consists of the necessary foundation excavation for box culverts and bridges.
420.2MATERIALS (Not Specified)
420.3CONSTRUCTION REQUIREMENTS
A.Depth of Excavation: The elevations of the bottoms of footings shown on the plans are approximate and the Engineer may order, in writing, such changes in elevations of footings as necessary. B.Treatment of Foundation: Rock or other hard foundation material will be free of loose material, cleaned, and cut to a firm surface. The surface may be level, stepped, or serrated as approved by the Engineer. Where concrete is placed on an excavated surface other than rock, special care will be taken not to disturb the bottom of the excavation. Concrete will not be placed until the depth of excavation has been checked and the suitability of the foundation material approved. Foundation excavation may be trimmed to the exact size of the footing and the footing forms omitted, when approved by the Engineer. Removal of unstable material below the bedding grade of box culverts will be performed as set forth in Section 421. Where foundation piles are used, the excavation of each foundation bed will be completed before the piles are driven. After the pile driving is completed, loose and displaced material will be removed or compacted to a smooth solid bed at or below plan elevation. C.Disposal of Excavation Material: The excavated material will be used for backfill and embankment or disposed of as directed. Excavated material will not be placed in stream beds. D.Preservation of Channels: Excavation will not be made outside of caissons, cribs, cofferdams, steel piling, or sheeting and the natural stream bed adjacent to the structure will not be disturbed. If any excavation or dredging is done at the site of the structure before caissons, cribs, or cofferdams are in place, the Contractor will backfill all excavation to the original ground surface or stream bed with satisfactory material after the foundation is in place. E.Cofferdams and Cribs: Cofferdams and cribs will conform to the requirements of Section 423. F.Inspection: The Engineer will be notified as soon as each excavation is completed. Concrete or piling will not be placed until the Engineer determines that the depth and size of the excavation and the foundation material are acceptable. 420 Page 288G.Backfill above Bedding Grade : Material used for backfill will be of an acceptable quality and will be free from large or frozen lumps, wood, and other extraneous material. Spaces not occupied by abutments, piers, or other permanent work will be backfilled to match the surface of the surrounding ground, with a sufficient allowance for settlement. Backfill will be satisfactorily compacted in horizontal layers not to exceed 6 inches loose depth. The slope bounding the excavation for abutments and wingwalls will be stepped or roughened to prevent wedge action of the backfill against the concrete. Backfill placed around box culverts, columns, piers, and walls will be deposited equally on both sides of the structure. Backfill will be compacted in accordance with Section 120.
420.4METHOD OF MEASUREMENT
Excavation for drilled-in foundations will be measured as set forth on the plans. The removal of water will not be considered a measurable item nor will allowance be made for duplication, sloughed material, or material removed due to mud flows. The plan shown quantity will be the quantity accepted for payment. Field measurements for structure excavation quantities will not be made, unless the Department determines that conditions warrant such measurement. Structure excavation will be measured to the nearest cubic yard. A.Structure Excavation, Bridge: The volume of an old structure or the volume of excavation performed as part of the removal of an old structure will be included in the pay quantity of excavation for the new bridge. The excavation allowed above the plan shown bedding grade for piers and abutments will be that volume bounded by vertical planes 18 inches outside of and parallel to the neat lines of the footings regardless of the volume of material actually excavated. Authorized excavation below the plan shown bedding grade will be that volume actually removed within the limits bounded by vertical planes 18 inches outside of and parallel to the neat lines of the footings. When foundation piles are used, no measurement will be made for excavation below the plan shown bedding grade unless the Engineer orders the foundation lowered. Measurement will not be made for excavation necessary for foundation seals. The plan shown line denoting the lower limit of unclassified excavation, or the as constructed line in the event it is lower, will be considered the upper limit for structure excavation with the following exceptions: The existing ground line will be considered the upper limit for structure excavation if, at the time of foundation excavation, the existing ground line is lower than the plan shown line denoting the lower limit of unclassified excavation or a line denoting the lower limit of unclassified excavation is not shown on the plans. B.Structure Excavation, Box Culvert: When a box culvert is constructed at or above the specified flow line, the plan shown quantity of structure excavation will be the pay quantity. 420 Page 289This quantity of excavation is equal to the theoretical volume of concrete below the box culvert flow line. When the Engineer orders the box culvert flow line lowered on construction, the material excavated between the plan shown box culvert flow line and the as constructed box culvert flow line will be measured for payment as unclassified excavation unless it is unstable material and must be removed by a dragline, backhoe, or similar equipment in which case it will be measured as structure excavation. C.Structure Excavation, Retaining Wall: Measurement will not be made for structure excavation, retaining wall. Plans quantity will be used for payment. D.Structure Excavation, Miscellaneous: Measurement will not be made for structure excavation, miscellaneous. Plans quantity will be used for payment.
420.5BASIS OF PAYMENT
Payment for work under this item will be made at the contract unit price per cubic yard for structure excavation, bridge; structure excavation, box culvert; structure excavation, retaining wall; or structure excavation, miscellaneous. In the case of piers and abutments for bridges, excavation ordered by the Engineer below the plan shown bedding grade will be paid for in accordance with Section 4.2. In the case of box culverts, payment for excavation of unstable material which must be removed by means of a dragline, backhoe, or similar equipment will be as per Section 421.5 . Work that is classed as unclassified excavation will be paid for at the contract unit price for unclassified excavation, or as extra work when an item of unclassified excavation is not provided in the contract. Payment will be considered full compensation for furnishing materials, labor, equipment, tools, and incidentals, including furnishing, installing, and removing any cofferdams, cribs, sheeting, or other temporary works necessary to complete the work. 421 Page 290421 BOX, PIPE, AND PLATE PIPE CULVERT UNDERCUTTING
421.1DESCRIPTION
This work consists of the removal of unstable material and rock, either in ledge or boulder formation, below the bedding grade of box, pipe, and plate pipe culverts, and the backfilling of undercut areas.
421.2MATERIALS
A.Backfill Material: Material for backfilling the undercut areas of pipe and plate pipe culverts will consist of stable material free of organic matter and rock. When specified in the plans or as required by the Engineer the backfill material will conform to that used for backfilling undercut areas of box culverts. If backfill material conforming to that used for backfilling undercut areas of box culverts is not included in the plans but is required by the Engineer, the Engineer will process a CCO to provide for compensation to the Contractor for the added cost of the changed material. Material for backfilling the undercut areas of box culverts will conform to the following: Sieve % Passing 1 1/2 inch 100 1 inch 95 - 100 #4 0 - 75 #200 0 - 18.0 If undercut depth exceeds 3 feet below the bottom of the structure and stable material is not encountered, oversized rock material may be used up to the bottom of the undercut limits shown on the plans. B.Bedding Material: Bedding material for precast concrete box culverts and granular bedding material when required for pipe culvers will be sand or selected sandy soil conforming to the following: Sieve % Passing 3/8 inch 100 #200 0 - 10.0 C.Extruded Insulation Board (Polystyrene): Extruded insulation board (polystyrene) will conform to AASHTO M230.
421.3CONSTRUCTION REQUIREMENTS
A.General: If the Engineer determines field conditions warrant change, the plan limits of the undercutting may be increased, decreased, or eliminated. The width of undercutting for pipe culverts will be the outside diameter of the pipe plus 4 feet or the outside span of arch pipe plus 4 feet. If the undercut material is disposed of, the disposal will be at locations acceptable to the Engineer.