- 453 - SECTION 702 -- EXCAVATION FOR STRUCTURES
702.01 Description
1.Bridges and the steel/concrete st ructures specified in Division 700 may require excavation as part of their construction, and this excavation is distinguished from the roadway excavati on specified in Section 200. This work shall consist of all excavation for the following:
a.Bridge foundations: (1) Abutments. (2) Piers. (3) Bents.
b.Concrete seals.
c.All culverts. d. Structural plate pipe. e. Headwalls and wingwalls. f. Retaining, MSE and Modular Block walls. g. Steps. h. Any and all other structures described in Division 700 or shown in the contract.
2.This work shall include the re moval of any obstructions within the excavation limits shown in the contract. It shall include all necessary bailing, draining, pumping, sheathing, and the construction of cofferdams or temporary cribs and their subsequent removal. The work shall also include backfilling, compacting, and the dispos al of any excess material obtained from such excavation.
3.All excavation shall be performed in compliance with current OSHA standards.
702.02 Material Requirements
1.Backfill materials shall be approved by the Engineer. 2. "Granular Backfill" meeting the requirements specified in Subsection 1033.02, Paragraphs 1., 2., and 3. or 6. and the requirements in Tables 1033.02A, 1033.03A or 1033.06 will be acc eptable. "Clay lump" and "mortar-making" proper ties do not apply.
702.03 Construction Methods
1.Substructure Excavations:
a.The Contractor shall excavate a volume large enough to contain the structure an d its forms and provide access to set, strike, and inspect the work (18 inch (450 mm) la teral spacing is generally adequate access).
b.Footings on soil: (1) If water is encountered, the Contractor shall dewater the excavation.
2.The water level shall then be maintained at an elevation below the base of the excavation until after the concrete has been placed and set for at least 5 hours.
702.03 Excavation for Structures
- 454 - (3) If water percolates through the base of the excavation in spite of dewatering efforts, then:
i.The Contractor shall pl ace a watertight seal course in the bottom of the excavation. This will be considered extra work. (ii) The Contractor shall prevent seepage through the cofferdam's walls. Such seepage shall not be justification for the placement of a watertight seal course except as noted in Paragraph 1.b.(3) of this Subsection.
4.If unsuitable soil is encountered at the elevation established for the bottom of the excavation, the excavation shall be continued to a width and depth desig nated by the Engineer. The unsuitable material shall be disposed as directed by the Engineer. The additional volumes excavated shall be replaced with compacted approved granular material, crushed rock or crushed concrete meeting the gradation requirements of Subsection 702.02 pa ragraph 2. The material shall be compacted to optimal stiffness as defined by a deflection target value established by the Engineer.
c.Footings on rock: (1) Spread footings which are supported by bed rock shall be founded on horizontal surfaces cut at least 6 inches (150 mm) into the rock.
2.The entire bottom surface of the footing shall be in contact with the rock.
3.Footings shall be constructed to the elevations shown in the contract.
i.If the rock is not a hard, solid, and a continuous stratum, then the excavation shall be continued until rock which will furnish the required support is found. (ii) If a satisfactory foundation is found more than 3 feet (1 m) above, or if a satisfactory foundation is not found within 2 feet (600 mm) below the elevation shown in the contract, the work shall be suspended. (iii) The Department will re evaluate the design before work resumes.
4.All footings on rock will be inspected by the Geotechnical Unit before concrete is placed.
2.Excavating for Pipe and Pipe-Arch Culverts: a. Pipe and Pipe-Arch Culverts constructed on soil: (1) The trench width at its bottom shall be at least 36 inches (1 m) wider than the width of the pipe.
2.All backfill will be placed as described in Paragraph 3. of this Subsection.
3.Bedding, described as shaping the trench to the pipe's diameter, including recesses for connections, shall be required for all pipe with a diameter greater than 2 feet (600 mm). Bedding shall include shaping the trench to not less than 10% of the total culvert height. Excavation for Structures 702.03 - 455 - b. Pipe and Pipe-Arch Culverts constructed on rock:
1.When rock, cobbles, or boulders are encountered in the bottom of a culvert excavation, the ro ck shall be excavated to not less than 6 inches (150 mm) below the lower surf ace of the culvert and replaced with proper bedding material.
2.No part of a culvert shall re st directly in contact with rock.
c.Unsuitable soil encountered at the bottom of pipe trenches shall be excavated, disposed as direct ed by the Engineer, and replaced with compacted approved granular material, crushed rock or crushed concrete meeting the gradation requi rements of Subsection 702.02 paragraph 2.; the material shall be compacted to optimal stiffness as defined by a deflection target value established by the Engineer.
3.Backfilling:
a.All structures shall be backfilled in accordance with the following requirements:
1."Granular Backfill" limit s are identified in the contract.
2.Backfilling shall not dama ge any part of the structure.
3.Backfill shall be placed in layers approximately 6 inches (150 mm) thick.
4.Backfill layers shall be comp acted to optimal stiffness as defined by a deflection target value established by the Engineer .
5.Backfilling shall not be st arted against any structure until the concrete develops a compressive strength of at least 70% of the design compressive strength.
6.Backfilling culverts, abutments, wingwalls, and piers shall progress concurrently on all sides.
7.Backfilling of retaining walls and abutments is limited to the top of berm elevat ion until the superstructure is in place.
8.All form boards or other obstructions shall be removed from drain or weep holes and any other structure before backfilling.
9.When the area to be backfilled has standing water, the area shall be drained or pumped until dry. Saturated unstable material shall be removed from the base.
i.If a suitable draining or pumping procedure cannot produce a dry area, an approved granul ar material shall be deposited to an elevation above the water level.
10.The Contractor shall use all available suitable backfill material before obtaining borrow.
11.The Contractor shall protect backfill from washing away or other erosion until the contra ct is complete and accepted by the Engineer.
12.Backfill for areas which provide support for any subsequent surface or base course, wh ich includes the area directly below the pavement section of the bridge ap proach slab, shall be constructed in
702.03 Excavation for Structures
- 456 - accordance with the requirements of Subsection 205.03 for Class III embankment and meet the compacti on criteria in Table 702.01. Table 702.01 Structure Backfill Requirements Depth Below Moisture Requirements Soil Type Finish Grade Minimum Maximum Silt-Clay Upper 40 in (1 m) Opt. -3% Opt. +3% Silt-Clay Depths > 40 in (1 m) ** Opt. +2% Granular All Depths ** ** ** Moisture content as necessa ry to obtain stiffness.
b.Only suitable material shall be used for backfill.
1.Materials such as frozen soil, logs, stumps, sod, weeds, or other organic matter shall not be used.
2.The Engineer may approve the use of large stones more than 12 inches (300 mm) in diameter if all voids between the large stones are filled with compacted soil.
3.Shales and other materials that break down during compaction shall not be used.
c.Granular Fill: (1) "Granular Backfill" limit s are identified in the contract.
2.Underneath the approach slab sections excavated by the Contractor, the interior of all abutme nts and wingwalls and tie rod trenches shall be backfilled with granular backfill.
d.Temporary shoring: (1) In lieu of excavating to construct the abutment substructure and then backfilling to t he limits shown on the granular backfill detail, the Contractor may utilize ot her methods to achieve a minimum of 3 1/2 feet (1.1 m) of clear excavati on from the inside abutment and wing faces.
2.If this option is elected, the 3 1/2 feet (1.1 m) wide void shall be backfilled with "Granular Backfill" from the bottom of the void to the bottom of the approach slab; and a mini mum depth of 1 foot (300 mm) of granular backfill shall be placed and compacted under the remaining approach slab section.
e.Backfilling bridges:
1.The Contractor shall comp lete the backfill at bridges to the elevation shown in the contract. The backfilled surface shall be a smooth continuation of the surrounding ground.
2.The Contractor shall compact backfill around bridge abutments, wingwalls, piers adjacent to ra ilroad tracks, piers in the toe of embankment slopes, piers for grade separations, culverts, inlets, sewers, and all other structures shown in the contract.
3.When tie rods are requir ed, the abutment and wing backfill shall be placed and compacted to an elevation matching the planned tie rod elevations. The tie rods shall then be installed and the backfilling operation continued. The contractor may trench the tie rods after the abutment and Excavation for Structures 702.03 - 457 - wing backfill. If the tie rods are trenc hed after the abutment and wing backfill, the tie rods shall be backfilled with granular material.
4.The volume to be compacted adjacent to bridges shall be the entire embankment between the faces of the abutment walls and vertical planes 10 feet (3 m) outside and par allel to the ends of the floor.
5.The entire area between the wings of box culverts and bridges shall be compacted.
6.Abutments shall not be backf illed to the full height until the superstructure (except bridge slabs) has been placed.
f.Backfilling culverts: (1) The Contractor shall place and compact embankments near pipe and box culverts in accordance with the requirements of Subsection 205.03 for the class of em bankment and type of compaction shown in the contract.
2.The area beneath and adjacent to pipe and pipe-arch culverts shall be backfilled carefully to insure the specified stiffness is achieved. Backfill shall be placed concurrently in equal lifts on both sides of the culvert.
3.When the full embankment over a pipe culvert is not immediately placed, the embankment sha ll be constructed to the elevation of the original surrounding ground surfaces or at least to the midpoint of the culvert’s vertical height (or to the elevation of the widest dimension of a pipe-arch culvert), with berm tops 2 feet (0.6 m) wide and with 1 vertical to 2 horizontal slopes away from the cu lvert. When the full embankment over a box culvert is not immediately pl aced, the embankment around the foundations shall be backfilled to at least the elevation of the original surrounding ground surfaces, but no lowe r than the top of the foundations. If necessary, additional excavation for backfill or embankment shall be required for this work.
4.Backfill for traffic:
i.Culverts having 2 feet or more depth of excavation, within 15 feet of traveled way shall be ba ckfilled to 15 feet minimum from the edge of the traveled way prior to remo ving traffic control. Backfill for traffic shall be to the final grade or to the lim its shown in Figure 702.01. Additional excavation for culverts may be required. (ii) The Engineer may also determine that it is necessary or desirable to allow vehicles (construction or otherwise) to travel over a pipe or box culvert. The volume to be compacted adjacent to the pipe or box culvert shall be that between vertical pl anes located 5 feet (1.5 m) outside of and parallel to the neat lines of the pi pe or barrel at its maximum horizontal dimension and a 1 vertical to 6 horizontal slope to natural ground line. Compacted soil shall be placed to a depth at least 3 feet (1 m) above the top of the box or pipe and to the grade of the existing adjacent shoulder slope on extensions. The remaining length of the pipe or box culvert shall be filled in accordance to pipe culverts in 702.03 Paragraph 3.f.(3). (iii) After the pipe is laid or as soon as the box culvert concrete reaches 3000 psi compressive strength, the Contractor shall complete the backfill within 10 calendar days.
702.03 Excavation for Structures
- 458 - (iv) Failure to complete the backfill within 10 calendar days shall be cause for the assessment of liquidated damages in the amount of $500 per working day until the backfil l is completed. “Completion of the backfill” shall be defined as the time when all of the required material has been placed, compacted, and shaped.
v.The Engineer may extend the 10 calendar days because of weather and soil conditions. (vi) The assessment of all liquidated damages described in Section 702 shall be in addition to any applicable liquidated damages assessed in accordance with Subsection 108.08.
4.Excess Material Disposal: a. The Contractor shall waste at the site or remove any excess material as approved by the Engineer.
b.No material shall be placed so as to permanently obstruct the flow of waterways except as shown in the contract.
5.Unsuitable material which in the opinion of the Engineer cannot be utilized in the fill shall be removed fr om the project and disposed at an approved site.
702.04 Method of Measurement
1.a. Excavation for individual br idge piers, bents, and abutments is not a field measured quantity. The pay item is a Lump Sum.
b.Tie rod excavation is in cluded in the bridge abutment excavation.
c.In the event that a bridge is constructed with a change in plans or with a change in the location, the payment may be recomputed. Excavation for Structures 702.04 - 459 - 2. Excavation for pipe culverts, headwalls, and box culverts is measured by the cubic yard (cubic meter). The quantity of excavation is computed by the Department using Figure 702.01 and the following limits described below: EXCAVATION PAYMENT LIMITS EXCAVATION DEPTH Dia. + 38 Feet (11.5 m) 19.0 Feet or Greater (5.75 m) Dia. + 28 Feet (8.5 m) 14.0 Feet to 19.0 Feet (4.25 m to 5.75 m) Dia. + 18.0 Feet (5.5 m) 9.0 Feet to 14.0 Feet (2.75 m to 4.25 m) Dia. + 8 Feet (2.4
m.4.0 Feet to 9.0 Feet (1.25 m to 2.75 m) Dia. 0 Feet to 4.0 Feet (0 m to 1.25 m) Dia. + 3 Feet (0.9 m) Figure 702.01
a.The upper limits will be the new channel section elevations, when shown in the contract, or the ground elevations, when a new channel section is not shown in the contract.
b.The horizontal limits to be used in computing the quantity of excavation will be as follows:
1.Concrete Footings. Vertical planes 18 inches (450 mm) outside of and parallel to t he limits of the footings.
2.Headwalls. Vertical planes 18 inches (450 mm) outside of and parallel to the limits of the headwalls.
3.Pipe Culverts. Vertical planes parallel to the centerline of the pipe culverts separated by a distance equal to the nominal inside diameter of the pipe, plus 36 inches (9 00 mm), and vertical planes 18 inches (450 mm) beyond the ends of the culvert.
4.Pipe-Arches. Vertical planes parallel to the centerline of the pipe-arch separated by a distance equal to the maximum nominal inside clear span dimension of the pipe-arch, plus 36 inches (900 mm), and vertical planes 18 inches (450 mm) beyond the ends of the culvert.
c.The lower limits to be used in computing the quantity of excavation will be as follows:
i.Concrete Footings. The bottom of the footings or to the lower limits of unsuitable material removed at the direction of the Engineer.
702.04 Excavation for Structures
- 460 - (ii) Headwalls. The bottom of the headwalls. (iii) Pipe and Pipe-Arch Culverts. The flowline elevation of the culvert or to the lower limits of unsuitable material removed at the direction of the Engineer.
d.In addition to the above, the nominal volume, based on neat dimensions, for the portion of the curtain or cutoff wall below the bottom of the concrete footings will also be included for payment for box culvert excavation.
e.(1) Overlapping excavation volumes will be measured and deducted from the pay volumes so that a volume is only paid for once.
2.The overlap of removal excavation volume with an excavation volume required to construct new work will be deducted by subtracting the overlapping removal excavation volume from the new work excavation volume.
f.The excavation associated with the preparation of a structure or the removal of a structure shall be included in the quantity of excavation for pipe culverts and headwalls or excavation for box culverts when the structure is within the limits of exca vation for the culvert or its headwalls.
g.Deductions will be made for the volume of any intersecting structure, except for pipe or pipe-arch culverts, when the intersecting structure has a cross sectioned area of more than 16 square feet (1.5 m2) within the limits of culvert excavation as shown in Figure 702.02. DEDUCTION LIMITS Shaded area > 16 Ft2 Deduction Shaded area < 16 Ft2 No Deduction Dia. + 3 Feet Figure 702.02
h.When excavation depths exceed 4 feet (1.2 m), an additional horizontal allowance will be computed on the basis of Figure 702.01. The slope of trench walls shall be approxim ately 1 foot (300 mm) rise to 1 foot (300 mm) run.
i.The excavation limits may vary due to the bedding requirements shown in the contrac t. The quantity of excavation will be computed on the basis of Figure 702.01. Dia. Excavation for Structures 702.04 - 461 - j. The limits in figures 702. 01 and 702.02 are for measurement purposes only. Any changes in the excavation limits for the Contractor’s operations or that which is necessary to meet any safety requirement will not be cause for recalculation of the established quantity.
3.When the contract or special prov isions require a culvert to be built with shoring or sheet piling, then Figure 702.01 will be superseded by the location of the shoring and the sheet piling when determining the authorized volume of excavation for culverts and pipes.
4.a. When additional material is required for backfilling or for the construction of embankments as descr ibed in these Specifications, the quantity to be paid for will be the volume of the material actually removed measured in cubic yards (cubic meters) in its original position.
b.When it is impracticable to measure the volume of material actually removed in its original position, the quantity to be paid will be 1.4 times the volume of placed embankment (cubic yards) (cubic meters). Payment will not be made for any surplus material placed outside the specified limits.
5.a. When unsuitable soil beyond the excavation payment limits at a Pipe Culvert, Pipe-Arch Culvert, Headwall, or Box Culvert is removed and replaced, the pay volume of soil removed shall be 2 times the actual volume removed as Excavation for Pipe, Pipe-Arch, Culverts, and Headwalls.
b.When unsuitable soil beyond the excavation for abutments, piers and bents will be paid for as extra work.
6.a. "Granular Backfill" for br idges shall be the quantity shown in the contract.
b.The quantity for "Granular Ba ckfill" shown in the contract is computed in cubic yards (cubic meters) based on the lines and grades shown in the "Granular Backfill" detail s. In the event that a bridge is constructed with a change in contract or with a change in the location, the payment may be re-determined.
c.Deductions will not be made in the quantity of "Granular Backfill" when the Contractor elects to use a sheet pile wall to construct the abutment substructure in lieu of excavation.
7.When it is necessary to remove unforeseen obstacles at the direction of the Engineer and additio nal granular backfill is required, the removal and the additional "Granular Backfill" will be paid for as "extra work."
8.a. Backfill required by paragraph 3.f.(3) and 3.f.(4) of Subsection 702.03 is measured and paid for as “Excavation for Pipe, Pipe- Arch Culverts and Headwalls” or “Excavation for Box Culverts”.
b.Backfill beyond the berm limits in paragraph 3.f.(3) and 3.f.(4) of Subsection 702.03 is paid for under the pay item for the remainder of the surrounding embankment.
9.The Contractor shall use all su itable excavated material from a structure for the backfill. The Contractor shall dry the material that exceeds the maximum moisture requirements. If the material ex ceeds the maximum moisture requirements during excavation and the volume exceeds 200 cubic yards (cubic meters), the drying of the material in excess of 200 cubic yards (Cubic meters) will be paid for as “extra work”.
702.05 Excavation for Structures
- 462 - 702.05 -- Basis of Payment
1.Pay Item Pay Unit Abutment _____ Excavation Lump Sum (LS) Pier _____ Excavation Lump Sum (LS) Bent _____ Excavation Lump Sum (LS) Granular Backfill Cubic Yard (CY) [ C u b i c M e t e r ( m3)] Excavation for Pipe, Pipe -Arch Cubic Yard (CY) Culverts, and Headwalls [Cubic Meter (m3)] Sheet Pile Excavation Cubic Yard (CY) [ C u b i c M e t e r ( m3)] Excavation for Box Culv erts Cubic Yard (CY) [ C u b i c M e t e r ( m 3 ) ]
2.No direct payment will be made for furnishing, placing, and removing cofferdams or cribs. This work shall be considered subsidiary to the item requiring the cofferdam or crib.
3.Removal of unforeseen obstacles which are unknown to both the Department and the Contract or at the time of receiving bids, and which, in the opinion of the Engineer, will be detr imental to the work of Excavation for Structures shall be "extra work", ex cept as noted in Subsection 104.06.
4.a. Direct payment will not be made for the following work which shall be considered as being subsidiary to the associated structure pay item:
1.Stepping slopes.
2.Placing or removing cofferdams and cribs. (3) Dewatering. (4) Backfilling or compacting. (5) Water used to facilitate compaction. (6) Drainage provisions at drains or weep holes.
7.The work involved in "bedding" pipes in trenches.
8.Sheeting and shoring. (9) Gravel, crushed rock, or other fill material (except as allowed in Paragraph 6. of this Subsection).
5.Box and pipe culvert excavation shall be the quantity shown in the contract.
a.The quantity will be increased by the amount of unsuitable material excavation calculated in Section 702.04 Para. 5.
b.The quantity will be recomput ed when the completed structure differs from the contract because of on e or more of the following changed conditions:
1.An increase or decrease in length of more than 10 feet (3 m). Excavation for Structures 702.05 - 463 - (2) A change in location, measured along the centerline of the project, of more than 10 feet (3 m).
3.A change in flow line elevation, at one or both ends of the structure, of more than 1 foot (300 mm).
4.An addition or deletion of any horizontal or vertical bend.
5.A change in the skew angle of more than 10 degrees.
c.If the Engineer and the Cont ractor agree, in writing, that no significant change in excavation has resu lted from the occurrence of one or more of the conditions listed above, then the quantity of excavation need not be recomputed.
6.Direct payment will not be made for any excavation required in connection with the construction of pipe culverts, median inlets, and flared- end sections or other appurtenances whic h are a part of the median culvert items shown in the contract. This work shall be considered subsidiary to the items for which the contract provides that direct payment will be made.
7.a. Additional excavation for backfill and embankment for pipe culverts, headwalls, and box culverts will be paid at the item's contract unit price, "Excavation for Pipe or Pipe -Arch Culverts and Headwalls" and "Excavation for Box Culverts".
b.Embankment placed above the limits specified in Subsection 702.03, Paragr aph 3.f.(3) shall be incl uded with appropriate earthwork pay item ["Excavation", "Excavation Borrow", "Excavation (Established Quantities)", or "Earth work Measured in Embankment"].
c.The quantity of additional excavation for culvert backfill shall be subtracted from the appropriate ea rthwork pay item, if applicable [“Excavation”, “Excavation Borrow”, “E xcavation (Establis hed Quantities)”, “Earthwork Measured in Embankment”]. Figure 702.01
702.05 Excavation for Structures
- 464 - 8. a. When compacted approved granular material, crushed rock or crushed concrete is placed for a st ructure foundation, payment will be “Granular Backfill”.
1.When “Granular Backfill” is not included in the Bid Proposal Schedule of Items and is the required backfill material to replace unsuitable material approved by the Engineer for removal, then the unit price for the replacement granular backfill shall be a negotiated unit price.
2.Each day, the Engineer and the Contractor shall compare their records of unsuitable material removed and reconcile any differences.
b.Gravel or crushed rock will not be paid for as “extra work” when placed at the bottom of a foundat ion if the material is not required structurally and is being provided solely as a good working platform for the Contractor.
9.When it is necessary to lower the elevations of bridge foundation beds, the additional excavation will be measured for payment as "extra work".
10.The quantities of unsuitabl e material excavated beyond the excavation limits shown in the contract and removed at the direction of the Engineer will be paid as "extra work."
11.Deductions will not be made in the price paid for excavation when satisfactory foundation beds for spr ead footings are found at elevations within 36 inches (900 mm) above the elevations shown in the contract; however, when it is necessary to lo wer the elevations of these foundation beds or to remove unsuitable material as directed by the Engineer, the additional excavation will be paid for as "extra work".
12.Payment is full compensation for all work described in this Section. - 465 - SECTION 703 -- PILES AND PILE DRIVING
703.01 Description
1.This work shall consist of furn ishing, driving, cutting, and extending all bearing and sheet piles. They shall be driven or placed in accordance with the requirements of these Specific ations at the locations, elevation, penetration, and bearing shown in the contract.
2.Only one type of concrete piling may be used in any one structure. Before construction begins, the Contra ctor shall advise the Engineer in writing which type is to be furnished at each structure.
703.02 Material Requirements
1.All materials shall conform to the requirements in Table 703.01. Table 703.01 Material Requirements Applicable Materials Section Portland Cement Concrete ....................................... 1002 Reinforcing Steel ....................................................... 1020, 1023, 1024 Epoxy Coated Reinfo rcing Steel ............................... 1021 Structural Steel (B earing Pile s) ................................. 1045 Steel Sheet Piles and Sheet Pile Corners ................. 1056 Sheet Zinc ................................................................. 1053 Sheet Alum inum........................................................ 1054 Precast P iles ............................................................. 705
2.Steel Piling:
a.Pipe pile shall meet the requirements in ASTM A 252, Grade 2.
b.Sheet pile and sheet pile corners shall meet the requirements in ASTM A 328/A 328M.
c."H" pile shall meet the requirements in ASTM A 6/A 6M.
3.Pre-Cast Piling:
a.Pre-cast concrete piling shall meet the requirements in Section 705.
4.Cast-In-Place Concrete Piles:
a.Piles shall be constructed in accordance with the details shown in the contract.
b.Materials: (1) The class of concrete used in cast-in-place concrete piles shall be as shown in the contract. Maximum slump for concrete used in cast- in-place piling shall be 6 inches (150 mm).
2.When the contract allows for the use of more than one class of concrete, the Contractor shall ad vise the Engineer, in writing, of the class of concrete to be used 14 da ys before the date of beginning the concrete work.
3.No change shall be made in the concrete class without written permission of the Engineer.
4.Reinforcement shall be furnished, handled, stored, and placed in accordance with the r equirements of Section 707.
Source: Nebraska Standard Specifications for Highway Construction, 2017 Edition. Pages 487–498 of 1,048.