204Excavation and Backfill for Structures

- EXCAVATION AND BACKFILL FOR STRUCTURES EXCAVATION AND BACKFILL FOR STRUCTURES

204.1DESCRIPTION

Excavate for the structures as shown in the Contract Documents. Unless specified otherwise, backfill the completed structures to the original ground line. B I D I T E M S U N I T S Class * Excavation Cubic Yard Concrete for Seal Course (S et Price) Cubic Yard Foundation Stabilization Cubic Yard Foundation Stabilization (Set Price) Cubic Yard Granular Backfill Cubic Yard Granular Backfill (Wingwalls) (Set Price) Cubic Yard Granular Backfill (Wingwalls) (Set Price) Cubic Yard Water (Grading) (Set Price) M Gallon *Class of Excavation

204.2MATERIALS

Provide materials that comply with the applicable requirements. Concrete ................................................................................................................. SECTIONS 401 & 402 Aggregates for Concrete Not On Grade ................................................................. DIVISION 1102 Aggregates for Backfill .......................................................................................... DIVISION 1100 Water ..................................................................................................................... DIVISION 2400 Provide sand, or other aggregate that contains suffi cient binder to allow compaction and limit the flow of water through the material, as granular material for culvert bedding. Provide material with enough moisture to allow compaction. The Engineer w ill accept the granular bedding material based on visual inspection of the material placed on the project.

204.3CONSTRUCTION REQUIREMENTS

and Class II Excavation. Class I and Class II Excavati on is referenced to the Excavation Boundary Plane (a horizontal plane at a given elevation) shown in the Contract Documents.

Excavation Boundary Plane, within the limits specified.

Excavation Boundary Plane, within the limits specified.

Excavation. Excavation for structures other than bridges is also classified as Class III Excavation. Class III Excavation is the entire volume of whatever nature encountered, including water, within the limits specified. The water level for determining quantities is the water level during construction at which pumping or bailing is necessary to continue excavation.

ground before beginning the excavation for the structure. - EXCAVATION AND BACKFILL FOR STRUCTURES Excavate all foundations to the elevations and dimensions shown in the Contract Documents. If rock of the quality that will not erode is encountered in the toe wall excavation, the Engineer may a llow the toe wall to be keyed into the rock. Follow OSHA safety regulations for sloping the si des of excavations, using shoring and bracing as required. If material encountered below the foundation elevation will not support the structure, remove such material and replace with stable backfill material approved by the Engineer. Save excavated material for structure backfill. Dispose of surplus excavated material and excavated material unsuitable as backfill material. Provide temporary erosion a nd pollution control according to DIVISION 900. When a bridge is constructed in conjunction with a new roadway alignment or elevation, construct the roadway embankment (a minimum of 300 feet) at the bridge to approximate grade first, then excavate for the abutments.

groundwater. Construct and shore the cofferdams according to OSHA safety regulations. The minimum size of the cofferdams shall be greater than the limits for pay excavation. Extend the cofferdams below the bottom of the footing, or at least to an elevati on as near the bottom of the excavation as foundation conditions will allow. If necessary, dewater the cofferdams.

all piling, remove the loose and displ aced material in the foundation pit. If necessary, reshape and recompact the bottom of the excavation according to the Contract Documents.

top elevation of the footing, whichever is lower, excavate the footing as shown in the Contract Documents. No side forming is allowed below the top elevation of rock or shale, or below the top of the footing, whichever is lower. Cut spread footing bridge foundations in rock to within 6 inches of the bottom of footing elevation. Complete the excavation to the required elevation, using hand equipment. Do not use blasting excavation below the top of footing elevation. If the bottom elevation of the spread footing excavation is in shale, minimize the time the shale is exposed to the elements before placing the concrete footing. Pl ace the concrete footing within the time limits designated in the Contract Documents. Contact the Regional Geologist if the sh ale exposure exceeds the maximum time specified. Mitigate the effects of the shale exposure by excavating a minimum of 4 inches below the over-exposed shale to expose sound material. The Contractor has the option (at own expense) to negate the time limits imposed for exposure of the shale by placing a 4-inch (minimum) conc rete seal of Grade 4.0 concrete over the exposed shale before the specified time limits expire. If the Contractor chooses this option, excavate to 4 inches below the plan bottom of footing elevation so the bottom of footing elevation remains at the elevation designated by the Contract Documents. After the excavation is completed, and all loose material is removed from the footing, drill exploratory borings 1½ to 2 inches in diameter and 5 feet deep to verify the quality and soundness of the material below the bottom of the footing. Notify the Engineer before starting the exploratory borings. • For footings with an area of less than 12 square yards, drill the boring in the center of the footing. • For footings with an area of 12 square yards or gr eater, drill a boring within 3 feet of each corner of the footing. If an exploratory boring encounters unsound material, or if the material at the bottom of the footing does not match the material shown on the geology sheet in the Contract Documents, do not proceed with the construction of the spread footing until the site is reviewed by the Regional Geologist and a recommended course of action made.

to construct the foundation stabilization 6 inches thick, according to the details shown, or underrun the item when deemed unnecessary. When conditions require, the Engineer may approve a depth greater than 6 inches.

stabilization and a firm foundation is not encountered at the established grade for boxes or pipe culverts, the Engineer may approve the removal of unsound material and installation of suitable foundation stabilization material. - EXCAVATION AND BACKFILL FOR STRUCTURES Before this work is done, the Engineer will determine the limits of excavation for the material removal.

seal course according to the details shown. When the Contract Documents do not show a concrete seal course, but the bottom of the excavation can not be pumped free of water, the Engineer may approve the placement of a concrete seal course. When approved by the Engineer, construct a 3-inch seal course of commercial grade concrete below the bottom of footing elevation. If the Contract Documents call for foundation stabilization, and the Engineer determines the conditions require a concrete seal course as specified a bove, underrun the foundation stab ilization. The Engineer will consider alternate methods of sealing out the water. Th e burden of proof regarding an alternat e method of sealing out the water will be on the Contractor. If a concrete seal course is not shown in the Cont ract Documents, or the Engineer does not approve one, the Contractor may still place one at own expense. When the Contract Documents show constructing foundation stabilization, the Contractor has the option to construct a concrete seal course in its place. However, the concrete seal course will be paid for as foundation stabilization at the contract quantity and unit price. If a concrete seal course is constructed, uni formly consolidate the concrete without voids.

Remove all shoring, bracing and cofferdams before backfilling a structure. Use material from the structure excavation or material from the roadway excavation for the backfill of structures. If necessary, adjust the moisture content of the soil by adding water to or aerating the material. Place granular backfill as detailed in the Contract Documents. If the area for granular backfill is excavated beyond the theoretical limits of the granular backfill, fill the over-excavation with granular backfill material suitable for the conditions, and that meets the Engineer’s approval. Do not use hydraulic methods of backfill. After the designated cure period for a concrete structur e expires, wait at least 3 days before subjecting the structure to the pressures of backfilling or to live loads. If adverse curi ng conditions exist, the Engineer may extend this period. Provide for drainage at all weep holes in concrete st ructures. Unless drainage is provided for otherwise in the Contract Documents, place approximately 2 cubic feet of crushed stone or sand gravel at each weep hole. Place the backfill in horizontal layers evenly on all sides of the structure, a maximum of 8 inches thick (loose measurement). If the backfill is placed on only one side of a structure (such as abutments, piers, wingwalls), do not put excessive pressure against the structure. Prevent wedging action against the structure during the backfill. Bench the slopes bounding the excavation. Extend each layer of the backfill to the limits of the excavation or to the original ground line. Continuously level and manipulate the material during the placing and compacting of each layer of the backfill. Use a motorgrader where possible. Compact each layer as specified before placing the next layer. Drain all water from areas before backfilling. If backfill compaction is not required for piers, it is not necessary to drain the water from the pier excavations before backfilling. If it is impossible to drain the water, deposit thin layers of backfill material into the water. When placing backfill material into water, the compaction requirements do not apply until the backfill progresses to the point that all water is absorbed by the backfill material. Unless otherwise shown in the Contract Documents, backfill compaction is not required around piers, except piers adjacent to railroad tracks, roadways or in the toe slopes of embankments. If the Contract Documents provide for "Compaction of Earthwork", compact the back fill according to B compaction in SECTION 205. If the Contract Documents designate a moisture range for the embankmen t adjacent to the structure, use backfill material with uniform moisture cont ent within the specified range according to SECTION 205 . If the Contract Documents do not designate a moisture range, use backfill material with uniform moisture content adequate to produce the specified density.

ground line, continue the compacted back fill to the top of the re inforced concrete box. Place the backfill 10 feet wide on each side of the culvert for the full width of the roadway embankment. - EXCAVATION AND BACKFILL FOR STRUCTURES

granular backfill for wingwalls according to the details shown.

backfill for wingwalls according to the details shown.

204.4MEASUREMENT AND PAYMENT

the Contract Documents, the quantities shown in the Contract Documents for the various balances will be the quantities for which payment is made. If the Contract Documents have been altered, or if th e Engineer or Contractor questions the accuracy of the contract quantities at any location, either party may request the quantities involved be measured.

cross-sectioning the area. The Engin eer will compute the quantities (volume) by the average end area method. Where it is impractical to measure material by the cr oss-section method, the Engineer will use 3-dimensional measurements. Measurement will not include additional excavation required to mitigate the effects of over-exposed shale in foundations.

the Contract Documents show excavation dimensions, the measured quantity is limited to the volume bounded by vertical planes at the contract dimensions. When excavation dimensions are not shown in the Contract Documents, the quantity measured for payment is the quantity removed, limited to the vol ume bounded by vertical planes 2 feet outside the footings and tie beams.

Engineer will measure Class III excavation by the cubic yard. If not shown as a bid item in the Contract Documents, Class III excavation for structures other than bridges is subsidiary to other items of work. If the Contract Documents show excavation dimensions, the measured quantity is limited to the volume bounded by vertical planes at the contract dimensions. When excavation dimensions are not shown in the Contract Documents, the quantity measured for payment is the quantity removed, lim ited to the volume bounded by vertical planes 2 feet outside the footings. Excavation for reinforced concrete box culverts, pipe cu lverts or headwalls for culverts is not measured for payment. Excavation over the culvert n ecessitated by the imperfect trench me thod of backfill is not measured for payment. If rock is not shown in the Contract Documents and is encountered during the excavation for reinforced concrete box culverts, pipe culverts or headwalls for cu lverts, the rock excavation is paid for as Extra Work, SECTION 104.

(either shown in the Contract Documents or approved by the Engineer) by the cubic yard. The quantity measured for payment is the quantity placed, lim ited to the volume bounded by vertical planes at the limits of the pay excavation for the structure. If the excavation for the structure is subsidiary, the quantity of concrete measured for payment is the quantity placed, limited to the volume bounded by vertical planes 2 feet outside the footings. If the Contractor elects to use a c oncrete seal course in place of th e foundation stabilization shown in the Contract Documents, the Engineer will measure and pay fo r the concrete seal course as the foundation stabilization at the contract quantity and at the contract unit price. The excavation necessary to place the concrete seal course is not measured for payment.

construct it, the Engineer will measure the foundation stabilization for box and pipe culverts by the cubic yard to the volume bounded by vertical planes at the contract dimensions to a depth of 6 inches, or greater depth approved by the Engineer. If the Contractor deems the foundation stabilizati on unnecessary, the Engineer will underrun the item. The Engineer will not measure excavation n ecessary to place the foundation stabilization.

by the cubic yard. The quantity measured for paymen t is the quantity placed, limited to the volume bounded by vertical planes at the limits of the pa y excavation for the structure. If the ex cavation for the structure is subsidiary, the quantity of foundation stabilization measured for payment is the quantity placed, limited to the volume bounded by vertical planes 2 feet outside the footings. - EXCAVATION AND BACKFILL FOR STRUCTURES The excavation necessary to place th e foundation stabilization (Set Price) is not measured for payment.

Engineer will measure granular backfill by the cubic yard. The Engineer will measure to the neat lines shown in the Contract Documents. The Engineer will not measure fo r payment the excavation required to place the granular backfill or any granular b ackfill material placed beyond the limitss hown in the Contract Documents (over- excavated areas).

M gallon, by means of calibrated tanks or water meters. Water used for dust control, water wasted through the Contractor’s negligence, water in excess of the quantity required to obtain the proper moisture content or water used for compaction of earthwork (backfill) around structures classified as bridges is not measured for payment.

"Foundation Stabilization", "Granul ar Backfill" and "Granular Backfill (Wingw alls)" at the contract unit prices is full compensation for the specified work. Payment for "Concrete for Seal Course (Set Price)", "Foundation Stabilization (Set Price)", "Granular Backfill (Wingwalls) (Set Price)" and "Water (Grading) (Set Price)" at the contract set unit prices is full compensation for the specified work. If the Engineer determines it is necessary to lower a footing below the elevation shown in the Contract Documents, the additional excavation is paid as follows:  Additional excavation up to and including 2 feet below the contract elevation is paid at the contract unit price.  Additional excavation from more than 2 feet up to and including 6 feet below the contract elevation is paid at 1½ times the contract unit price.  Additional excavation more than 6 feet below the contract elevation is paid as Extra Work, SECTION 104.