Effective with the December 2018 Letting 93 2019 Standard Speci fications Section 206 Excavation for Structures
206.1 Description
1.This section describes excavati ng for culverts, structural pla te pipe, and structural plate pipe arches, bridges, and retaining walls. It a lso describes removing old su bstructure units within the space occupied by the ne w structure.
206.2 Materials
1.Furnish backfill material of a quality acceptable to the engin eer and free from froz en lumps, wood, or other extraneous or perishable ma terial. The contractor may use engineer-approved material obtained from excavation.
2.If the contract specifies struc ture backfill, furnish material conforming to 210. The contractor may use material conforming to the requi rements for structure backfill obtained from excavation as specified under 104.8 .
206.3 Construction
206.3.1 General
1.Under the Excavation for Struct ures bid items, excavate materi al of whatever nature encountered. The department will not classify this e xcavation as common, rock, o r marsh excavation under 205 or as dry or wet excavation.
2.Remove logs, stumps, and other m aterials and obstructions nece ssary to place the foundations and structure. Dispose of material obtained from excavation. Backfi ll, compact, shape, slope, and clean the site.
3.Construct, and subsequently remov e, necessary cofferdams and c ribs or well-point systems, and the necessary sheeting, shoring, bracing, draining, and pumping to allow constructing the substructure, above the seal, in the dry. Do no t use stream diversions and ea rth dikes instead of specified cofferdams or well-point systems, unless the engineer authorize s in writing.
206.3.2 Excavation Depth
1.The elevation of the bottoms of footings, as the plans show, i s approximate only. The engineer may order, in writing, changes in dimensions or elevation of footin gs necessary to secure a satisfactory foundation.
206.3.3 Cofferdams and Cribs
1.If providing cofferdams and cribs for foundation construction, ensure that they are safely designed and constructed, carried to adequate depths and heights, and are ma de watertight as necessary for the proper performance of the work. C onstruct cofferdams and cribs so that interior dimensions give sufficient clearance for the cons truction of forms and the insp ection of their exteriors, and to allow pumping from sumps outside the forms. If cofferdams or cribs ti lt or move laterally during the process of sinking, right, reset, or enla rge them to provide the necess ary clearance. The contractor is responsible for any claims for damages resulting from the use o f a well-point system.
206.3.4 Protecting Concrete
1.Construct cofferdams and cribs to protect fresh concrete again st damage from a sudden rising of the stream and to prevent damage to the foundation by erosion. Plac e wales and cross braces at locations that allow construction of the su bstructure unit without constr uction joints other than those the plans show. If required to leave wales or braces in pla ce, use only p ipe, precast concrete or rolled steel sections. Do not box out with timber braces. 206.3.5 Plans Required
1.If the engineer requests, submi t one copy of signed and sealed plans as specified for cofferdams and cribs under 105.2 , showing the proposed method of cofferdam or crib construction for the file. At the engineer’s request, submit 2 additional copies of these plans f or review. If the engineer does not find the plans submitted for review s atisfactory, make the required changes. Whether or not the engineer requests submittal of the plans or concurs in the use of the pl ans as submitted or corrected, the department will not relieve the contractor of the responsibility to secure a safe and satisfactory cofferdam or crib.
206.3.6 Removal
1.Unless specified otherwise, remov e cofferdams or cribs, includ ing sheeting and bracing, after the completion and curing of the subs tructure unit. Exercise care n ot to disturb or otherwise injure the finished masonry. Effective with the December 2018 Letting 94 2019 Standard Speci fications 206.3.7 Excavation
1.Notify the engineer sufficiently before beginning excavation f or structures so the engineer may take elevations and measurements o f the existing ground and substruc ture units before disturbance and removal.
2.Excavate as specified in 29 CF R Part 1926 OSHA subpart P for excavations. Slope the sides of the excavation as required by soil conditions to stabilize the side s for safe working conditions. Limit excavation to the quantity consid ered necessary for safety. If the plans require, shore the excavation instead of sloping the sides. If the plans do not require shori ng, the contractor may elect to use, at no expense to the department, shoring rather than excavating to a slope. http://www.dol.gov/dol/cfr/title_29/
206.3.8 Preparing Foundation for Footings
1.Free rock or other hard foundation material of loose material. Clean and cut this material to a firm surface, either level, or ste pped, or serrated. Clean out and f ill seams with cement mortar or grout.
2.If masonry is to rest on an e xcavated surface other than rock, exercise special care not to disturb the bottom of the excavation. Do no t make the final removal of the foundation material to grade until just before placing the masonry. Pro tect surfaces from freezing afte r excavation and before placing concrete for the footing. Do no t place concrete on frozen subgr ade.
3.If using foundation piles, subst antially complete the excavati on of each pit before beginning pile- driving operations in the pit . After completing pile-driving op erations in a given pit, remove loose and displaced material in the pit to the elevation of the bottom of the footings.
4.If the contractor can place footings in dry foundation pits, i t may omit footing forms, with the engineer’s approval. In this case, fill the ent ire excavation with concret e to the elevation of the top of the footing.
5.For footings founded on sound rock , key them into the rock as the plans require. If required, conform the keyway to plan dimensions. F or footing excavations in sound rock, fill the footing with concrete to the elevation of the top of the rock or the top of the footing, whichever is lower.
206.3.9 Dewatering
1.If possible, dewater foundation excavations before depositing masonry within.
2.Pump from the interior of foundation enclosures in a manner to preclude, if practicable, removing foundation material or concrete ingredients.
3.Do not pump from the interior of a foundation enclosure while placing concrete in the enclosure or for at least 24 hours afterwards, unless done from a suitable sump outside the forms. Do not pump from within any foundation enclosure while depositing concrete under water in the enclosure. Do not begin pumping to dewater a sealed coffe rdam until the seal has set su fficiently to withstand the hydrostatic pressure, or until at least 3 days have elapsed since placing the seal.
206.3.10 Subfoundation Course
206.3.10 1 Bridges and Retaining Walls
1.If placing masonry on a soft, muddy, or muck-covered surface that will not dry ou t and harden if the excavation is kept dewatered for a reasonable length of time, furnish and place a subfoundation course if the engineer directs. Construct a subfoundation cours e of structure bac kfill conforming to 210, or other engineer-approved materi als. Place the subfoundation course directly below the elevation of the bottom of the footings to the depth the engine er designates.
206.3.10 2 Culverts
1.Place a 6-inch subf oundation course of s tructure backfill conf orming to 210, or other engineer- approved materials, directly below the elevation of the bottom of the slab between the cutoff walls of culverts.
206.3.10 3 Structural Plate Pipe and Pipe Arches
1.Place subfoundation courses, i ncluding bedding courses, for st ructural plate pipe and pipe arches as specified for erection in 527.3.2.
206.3.11 Foundation Seal
1.If the contractor encounters conditions th at make it impractic able to dewater the foundation excavation before placing the masonry, the engineer may require constructi on of a concrete foundation seal of necessary dimensions. After the seal sets, dewater the foundati on excavation and place the balance of the masonry in the dry. Place foundation seals the plans do not show below the bottom of the footing unless authorized other wise. Place concrete in foundation seals as specified for depositing concrete underwater in 502.3.5.3 . Effective with the December 2018 Letting 95 2019 Standard Speci fications 206.3.12 Inspection
1.Do not place any masonry or er ect any form or structural plate pipe or pipe arch in any excavation until the engineer approves t he depth of the excavation and the chara cter of the foundation material.
206.3.13 Backfilling
206.3.13 1 General
1.Backfill spaces excavated and no t occupied by the new structure to the elevation and section existing before excavation. Do not place backfill above the required sec tion for the finished work. If placing backfill, provide allowance for settlement.
2.Do not backfill substructure units, except as required for the safety of workers, unt il clearing the area involved of falsework , sheet piling, cribbing, shoring, bracing, forms, and rubbish. Backfill the cofferdams before removing the sheeting, unless the engineer al lows otherwise.
3.If required for the safety of workers, and with the engineer’s approval, the contractor may remove sheet piling, cribbing, shoring, and bracing as backfilling pro gresses.
4.Perform backfilling to prevent wedging action against the stru cture. Step, terrace , or treat existing slopes as necessary to prevent slipping and wedging of the back fill.
5.Unless specified ot herwise, place backfill in continuous horiz ontal layers no more than 8 inches thick. If practicable, uniformly raise l ayers on all sides of each sub structure unit or cu lvert. Surround the stone used in backfilling by finer material. Compact each layer , before placing the next layer, by using engineer-approved rollers or port able mechanical or pneumatic t ampers or vibrators.
6.If there is water in an excavati on, backfill to displace the water but not trap it within the excavation. Do not use water to expedite backfill settlement except with the e ngineer’s written approval. However, the engineer will not require the contractor to dewater the excavat ion before placing backfill. If allowed to use water, keep the entire exca vation inundated while placing b ackfill, except if jetting.
7.Conduct backfilling operations to a void damage or deflecting a ny portion of the structure out of alignment. Gradually deposit the backfilling material transport ed in trucks or other vehicles instead of dumping the entire contents as o ne mass. Lower clams, dippers, and similar backfill containers to within 5 feet of previously depo sited backfill, or of the water surface, before dumping.
8.The contractor may end dump bac kfill from the structure or app roach embankment if it intends to spread and place the end-dumped material in the above-described 8-inch horizontal layers. Do not place backfill in or from narrow ramps or driveways up to or fr om the structure.
9.Perform backfilling ar ound structural plate pipe and pipe arch es as specified for backfilling around pipe and pipe arches under 527.3.3.
10.Extend the backfill along the fr ont face of abutments, retaini ng walls, and wing walls to within 6 inches of the weep holes, unless designated otherwise.
11.If weep holes are designated on the plans for culverts, abutme nts, and retaining walls, deposit coarse gravel or crushed sto ne behind the culvert, abutment, or retain ing wall at the level of the weep holes according to dimensions the plans show.
12.Do not place backfill against any portion of any substructure unit until completing the required curing, surface preparation, dampproofi ng, and waterproofing of the wor k to be backfilled.
206.3.13 2 Self-Supported Abutments and Retaining Walls
206.3.13 2.1 General
1.Allow self supported structures to develop sufficient strength before backfilling.
206.3.13 2.2 Backfill on One Side of the Structure
1.The contractor may backfill structures tha t have attained the specified compressive strength or upon expiration of the minimum time periods tabulated below: GENERAL PURPOSE HIGH EARLY STRENGTH COMPRESSIVE STRUCTURE TYPE[1] CONCRETE CONCRETE STRENGTH i n days[2] in days[2] in psi Abutment type A1, A2, A5[4] 2 1 2000 Abutment type A3[3] 2 1 2000 Abutment type A4 14 7 3000 Full retaining abutments 14 7 3000 Box culverts[5] 14 7 3000 Retaining walls and end walls 14 7 3000 Effective with the December 2018 Letting 96 2019 Standard Speci fications [1] Abutment types: A1: Body about 5 feet tall wi th one row of piles. A2: Body about 5 feet tall wi th 2 rows of piles. A3: Body about 5 feet tall with backwall and 2 rows of piles A4: Body about 13 feet tall with bac kwall and 2 or more rows of pil es. A5: Body about 10 feet tall with one row of piles extending to within 2 feet of abutment top. Full retaining: Body extending from lower roadw ay/river elevati on to beam seats. [2] Only count days wher e the concrete temper ature did not fall be low 40 F. [3] Upon obtaining the required compressive strength, the contract or may backfill the bo dy of A3 abutments before placing the backwall. [4] Place and cure the superstruct ure before backfilling A5 abutme nts as specified in 206.3.13.3 . [5] Place and cure the top before ba ckfilling except as allowed un der 206.3.13.3 .
206.3.13 2.3 Backfill on Both Sides of the Structure
1.The contractor may backfill foot ings to the top of the footing s; sill abutments to the berm elevation; and retaining walls and piers unif ormly and simultaneously on both sides to the elevation of the front ground surface immediately upon removing the forms.
206.3.13 3 Rigid Frame Structures
1.Do not place backfill against an abutment or wall designed to gain support from a s uperstructure until placing and curing that superstructure.
2.The contractor may backfill 1/4 of the total wall height of a box culvert after attaining a wall compressive strength of 2000 psi. Do not c omplete the backfill until the top is placed and conforms to
206.3.13 2.2 .
206.3.14 Incorporating or Dis posing of Excavated Material
1.Incorporate excavated material in the work to the extent pract icable. Use materials with suitable engineering properties for ripr ap or backfill. If the contract contains the Excavation Common or Borrow bid items and embankment material is needed at the time of disp osal, use the balance of the excavated material, with suitable engineering properties, in th e embankment.
2.Dispose of surplus or unsuitable material as specified in 205.3.12 .
206.3.15 Preserving Channels and Waterways
1.Unless otherwise allowed, do no t excavate outside caissons, cr ibs, cofferdams, or sheet piling, and do not disturb the natural stream bed next to the structure. If per forming any excavation or dredging at the site of the structure before cais sons, cribs, or cofferdams are sunk in place, backfill these excavations to the original ground surface or stream bed with material sati sfactory to the engineer after placing the foundation.
2.After completing work within cofferdams, cribs, or sheet piling, backfill excavated areas within the cofferdams to the stream bed elev ation, unless specified otherw ise.
3.Remove excavated material and debris resulting from the contractor’s operations from stream channels, ditch lines, or waterw ays to the level of the finishe d streambed or ground line at no expense to the department. 206.4 Measurement
1.The department will measure the Ex cavation for Structures bid items as a single lump sum unit for each structure acc eptably completed.
2.The department will measure the Co fferdams bid items as a sing le lump sum unit for each structure acceptably completed. 206.5 Payment
206.5.1 General
1.The department will pay for measured quantities at the contrac t unit price under the following bid items: ITEM NUMBER DESCRIPTION UNIT 206.1000 Excavation for Structures Bridges (structure) LS 206.2000 Excavation for Structur es Culverts (structure) LS 206.3000 Excavation for Structures Retaining Walls (structure) LS 206.4000 Excavation for Structures Structural Plate Pipe or Pip e Arches (station) LS 206.5000 Cofferdams (structure) LS Effective with the December 2018 Letting 97 2019 Standard Speci fications (2) The department will pay for material excavated und er this sect ion and used in embankments at the contract unit price for Borrow , or absent the Borrow bid item, at the contract unit price for Excavation Common. The department will measur e material as specified for e xcavation in 205.4.1 .
3.The department will pay separately for foundation seals, the p lans show or the engineer directs, under the Concrete Masonry Seal b id item as specified in 502.5 .
4.The department will pay separately for excavating unforeseen s tructures found within the limits of the Excavation for Structures bid items. Unforeseen structures are man-made structures not visible when visiting the construction site and that the plans do not list o r show. The department will pay for removing all or part of a culver t or bridge as specified in 203.5 . The department will pay for excavating other unforeseen structures as ex tra work. Other removals visib le when visiting the construction site or that the plans list or show a re incidental to the work.
206.5.2 Excavation for Structures
1.Payment for the Excavation for Structures bid items is full co mpensation for removing and disposing of excavation, including excavating for seals, girders, projection s, and subfoundation courses; for preparing foundation; and for backfilling and compacting space excavated and not occupied by the new structure, including subfoundation course.
2.Payment also includes providing cofferdams, cribs, sheeting, s horing, bracing, pumping, and dewatering except, if the contract contains the applicable bid items, the department will pay separately for this work.
3.Payment is full compensation for excavation, removed to an ele vation between planes one foot above and below the plan elevation of the bottom of the footings or f loor of culverts, or the invert of structural plate pipe or pipe arches as the plans show for the specific un its.
4.If the footing is stepped, or on a slope, payment is full comp ensation for excavation to an elevation between planes lying one foot above and below the plan elevatio n of the bottom of the footing, for each stepped section; or excavation between planes lying one fo ot above, below, and parallel to the slope established by t he plan elevations for the bottom of the footing.
5.If the engineer orders any excavat ion be performed to elevatio ns in excess of one foot above or below the elevation of the bottom of t he footings or floor or invert as indicated on the plans, the department will pay for this excavat ion as extra work.
6.The department will pay separately for necessary clearing and grubbing under the Clearing and Grubbing bid items as specified in 201.5 .
7.The department will pay separately for structure backfill, if specified, under the Backfill Structure bid item as specified in 210.5 .
206.5.3 Cofferdams
1.Payment for the Cofferdams bid items is full compensation for providing cofferdams and cribs, including well-point systems, sheeting, shoring, and bracing; f or constructing, mai ntaining, backfilling, and removing cofferdams and cribs; and for pumping and dewateri ng. Effective with the December 2018 Letting 98 2019 Standard Speci fications Section 207 Embankment
207.1 Description
1.This section describes placing in embankments and in miscellan eous backfills, material obtained under the bid items in the road way and drainage excavation, bor row, or excavation for structures sections.
207.2 Materials
1.For embankment, use engineer-approved material containing no logs, stumps, brush, or other perishable material. The contractor may place excess unstable topsoil and other unstable soil in embankments outside the roadwa y foundation as defined in 101.3 . Do not place frozen soil in embankments within the roadway foundation.
2.For the top 8 inches of earth e mbankments, use materials free from large stone, rock, and broken concrete or other materials that significantly affect scarifyin g, compacting, and finishing the subgrade.
3.For those portions of embankments that the contractor proposes to bore holes for piling, or to drive piling through, use materials that do not contain stone or broken concrete retained on a 3-inch sieve and free from quantities of gravel, stone, or broken concrete p assing a 3-inch sieve or other material that significantly affects bori ng the holes or driving the pili ng.
207.3 Construction
207.3.1 General
1.Before placing embankment materials, complete any required cle aring and grubbing of the site and prepare the roadway foundation as specified in 205.3.2, unless the contract specifies otherwise.
2.Remove ice and snow from the ground surface before placing emb ankment on the ground. Do not place embankment on frozen subgrade.
3.Unless the contract specifies o therwise, discontinue construct ing embankments in the fall or early winter if weather conditions prevail that cause substantial fre ezing of the materials during placement, except if using materials from rock excavation, or of a granula r nature and that contain only minor quantities of silt, clay, loam, or similar materials. 207.3.2 Placing Layers
1.Construct an embankment starting at the lowest point of the fi ll, below the grade at the bottom of ravines. Construct the embankmen t in layers by spreading and le veling the material during placement. Spread individual layers evenly to uniform thickness throughout and approximately parallel with the finished grade for the full width of the embankment, unless dir ected otherwise. Place the material in layers generally no thicker than 8 inches, to secure the required compaction. On side hills too steep to operate hauling equipment, over low wet ground, in marshes, or if filling in water, provide a single layer, just thick enough to support the hauling equipment while placing subsequent layers.
207.3.3 Placing in Marsh
1.If constructing embankments in trenches excavated across wet m arshes or swamps, end dump the fill material. Begin filling at one end of the marsh and proceed acr oss the marsh, close enough to the excavating operations to allow the equipment to remove any disp laced peat or muck as it accumulates ahead of the advancing embankment toe. Place fill material in a way that, and to a height that, effectively displaces unstable material from within the area of the proposed embankment. Build temporary surcharges, as required, to the height and horizontal dimensions the plans show. Progressively move temporary su rcharges ahead as the embankment advances.
2.If excavating marsh areas in a dry condition, construct the em bankment in the excavation area in layers and compact it to t he extent practicable.
207.3.4 Placing Rock
1.If the material for embankment c onsists of rock, broken stone, or fragmented materi al of a size that makes placing in 8-inch layers impracticable, then place the em bankment material in layers no thicker than the approximate average size of the larger rocks. Avoid ne sting and fill the voids with smaller stones and satisfactory soil or rock fines.
207.3.5 Hydraulic Fills
1.If constructing embankments by the hydraulic method, obtain th e engineer's written approval as specified in 208.3 and construct as the engineer directs.
Referenced in this section
Excavation for Structures in other states
- Missouri 206 · Excavation for Structures
- Colorado 206 · EXCAVATION AND BACKFILL FOR STRUCTURES
- Michigan 206 · Excavation and Backfill for Structures
- Iowa 2402 · Excavation for Structures
- Illinois 502 · EXCAVATION FOR STRUCTURES
- Massachusetts 140 · EXCAVATION FOR STRUCTURES
- Nebraska 702 · EXCAVATION FOR STRUCTURES
- Ohio 503 · Excavation for Structures
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Source: Wisconsin Standard Specifications for Highway and Structure Construction, 2019 Edition. Pages 102–106 of 601. View official source ↗