2451Structure Excavations and Backfills

2451.1DESCRIPTION

This Work consists of excavating, preparing foundations, placing, and compacting backfill for Bridges and Structures per 1103, “Definitions,” either cast-in-place or prefabricated. This Work also consists of constructing and removing cofferdams, making soil bearing tests, and the disposing of surplus excavated Materials. The Department considers the following as cast-in-place Structures: Bridge Substructures, concrete box Culvert extensions, concrete retaining walls, footings for structural plate arches, 3 sided concrete boxes, concrete arches, and high mast light foundations. The Department considers the following as prefabricated Structures: precast concrete, prefabricated metal, or thermo plastic Structures including concrete box Culverts, pipe Culverts and sewers, cattle passes, and Subsurface drains.

2451.2MATERIALS

B Select Grading Material Unsuitable Materials include those Materials not meeting 1103, “Definitions: Select Grading Material,” and additional Materials deemed unsuitable by the Engineer. Provide Materials for special backfill, bedding, drain, or filter purposes as shown on the P lans.

2451.3CONSTRUCTION REQUIREMENTS

A General Requirements Prepare foundations to the elevations and grades shown on the P lans. Use temporary construction to place Structures or Substructures in open excavations under dry conditions. A.1 Site Preparations Clear and grub in accordance with 2101, “Clearing and Grubbing.” Clear and grub the entire area bounded by straight lines between the Structure extremities. If constructing Bridges, extend clearing and grubbing operations to the Right-of-way between the Bridge extremities. Remove tree branches that overhang the Structure and inhibit its function. Perform preliminary embankment construction in accordance with 2106, “Excavation and Embankment – Compacted Volume Method.” A.2 Elevations and Dimensions The Engineer may make adjustments, in writing, to the approximate elevations and dimensions of footings as shown on the Plans. The Engineer may make adjustments to the approximate location and orientation of box Culverts and pipe Structures as shown on the Plans. A.3 Temporary Construction Perform temporary construction Work to avoid unnecessary hazards or disruption to the permanent Work at no additional cost to the Department. Temporary construction may include sheeting, shoring, bulkheads, dikes, channels, drainage pipes, sluiceways, cofferdams, warning signs, and fencing as necessary.

Obtain the Engineer’s approval of detailed construction Plans and methods before starting temporary construction Work. A.3.a Cofferdams Construct cofferdams of sufficient size to allow pumping, and provide waterways outside of the forms. Include provisions to allow lowering the foundation elevation to 3 feet below the level shown on the Plans. Do not place cofferdam bracing against concrete forms or the Structure. The Contractor may extend steel bracing through poured concrete located below the final ground elevation. Do not box out braces or struts unless otherwise approved by the Engineer in writing. Remove cofferdams located within Roadbed embankments when no longer needed, to at least 4 feet below the Subgrade elevation. Remove cofferdams located in streams or lakes to the bottom of the stream or lakebed. Remove cofferdams located in established navigation channels to an elevation at least 2 feet below the established bottom of the channel. Remove other cofferdams to an elevation at least 2 feet below grade. A.3.b Concrete Foundation Seal If the Plans do not show a concrete seal, the Contractor may install a concrete seal within a cofferdam, if accepted by the Engineer. Perform the concrete seal construction, including necessary excavation, at no additional cost to the Department . Submit written notice to the Engineer indicating the planned seal thickness, sources of Materials, mix design, and method of concrete placement for approval by the Engineer. Place the entire seal below the foundation elevation for the Substructure shown on the Plans in accordance with 2401.3C, “Placement of Concrete – General Requirements.” A.3.c Pumping While pumping from within foundation enclosures, keep the foundation Materials intact and do not draw water through or over fresh concrete. The Contractor may pump during concrete placement and within 24 hours after concrete placement, if using a pump separated from the Work by a watertight wall or other means that prevent damage to the foundation. Do not begin pumping to dewater a cofferdam sealed with concrete until the seal has cured in accordance with the following minimum requirements:

cofferdam has been maintained at 70°F or greater;

maintained from 45°F to 70°F; or

cofferdam has been no greater than 45°F during the curing period. A.4 Restoration Work Restore the surface and general features of the excavation site after completion of the Work to the similar condition as before excavation, to the satisfaction of the Engineer.

A.5 Cold Weather Protection Place permanent or temporary backfill, or other insulating Material approved by the Engineer, to protect foundation soils against freezing and related heaving actions after casting footings or driving foundation piles. The Department will waive this requirement if the Contractor has only driven the test pile within the foundation at the time of freezing conditions. If frost heaving is evident, drive the test pile further when installing the rest of the foundation piles, as directed by the Engineer. B Excavating B.1 General Perform Structure excavation to allow the erection of forms, temporary construction, and compaction of backfill Materials, unless the Contract requires or the Engineer directs otherwise. B.2 Types The Department will classify excavation types in accordance with the following:

encountered or the conditions of removal.

of at least 1/2 cubic yard.

as shown on the Plans for waterway Bridges. The Department will consider the volume of removed Structures as a separate Contract Pay Item and will not include the volume of Structure removals within the excavation limits as part of the excavation volume. The Department will include the cost of Structure removals with other relevant Pay Items, unless otherwise required by the Contract. B.3 Cast-In-Place Structures The Engineer may reject the Work if water accumulates within the excavation and detrimentally affects the Structure or the stability of the backfill. Confine excavation in streams or lake beds within caissons or cofferdams . Repair disturbances to streams or lake beds using Materials approved by the Engineer. Complete necessary areas of excavation within sealed cofferdams before placing items, such as walers, struts, and other framework items, that may restrict the access to the excavation Equipment. B.3.a Earth Excavations If placing concrete on natural soil foundation without piling, as shown on the Plans, shape the bottom of the excavation to the dimensions and elevations shown on the Plans. Use vibratory methods to compact the foundation soils in accordance with 2106.3G, Compacting Embankments and Backfills.” Replace unsuitable foundation soils with Material as shown on the Plans and as directed by the Engineer. Replace Materials unnecessarily removed below the foundation elevation at no additional cost to the Department.

Complete excavation before beginning pile driving operations for each unit . After driving the piles, shape the bottom of the excavation to the elevation shown on the Plans. Use granular Materials meeting 3149.2D.1, “Granular Backfill,” to backfill excavations below the established elevation of the foundation at no additional cost to the Department. B.3.b Rock Excavation Do not remove Class R and Class W Materials encountered in the excavation, unless the Department classifies the excavation as Class U, until the Engineer measures the pay quantities for Class R and Class WR Materials. For footing foundations located in solid rock, remove the rock to the elevation as shown on the Plans for the entire area bounded by vertical planes through the neat lines of the footing. If the Plans do not show a footing elevation, remove the rock to an elevation no higher than the established elevation for the bottom of the footing or as directed by the Engineer. Remove rock without affecting the quality of the foundation. B.4 Prefabricated Structures B.4.a Earth Excavations If the Contract does not contain provisions for foundation preparation, excavate to provide uniform support under the entire Structure, to allow the placement of the Structure to the staked grade and line, and to allow for the installation of backfill Materials. If the Contract contains provisions for foundation preparation, excavate to provide the foundation thickness shown on the Plans and uniform Structure support. B.4.b Rock Excavations Expose, but do not remove Class R and Class WR Materials encountered during Class E or Class WE excavation, until the Engineer measures the pay quantities for Class R and Class WR Materials. Remove and replace unyielding Materials such as bedrock, boulders, or concrete located within 1 foot of the sides or the bottom of the Structure in accordance with 2451.3D, “Backfilling and Compacting Excavations,” and 2451.3C, “Foundation Preparations,” or as directed by the Plans and Special Provisions. C Foundation Preparations Prepare the Structure foundations in accordance with the following, except as modified by the Contract. Provide temporary construction, pumping, or other means to construct the S tructure in a dry excavation at no additional cost to the Department. C.1 Cast-In-Place Structures Remove disintegrated Material, loose Material, and thin strata rock from rock foundations. Clean and fill rock seams with concrete, cement mortar, or grout as directed by the Engineer. If the character of the natural foundation soil is unsuitable, provide additional excavation below the planned footing elevation as directed by the Engineer . The Engineer will direct the limits of the excavation and the placement of special backfill.

C.2 Prefabricated Structures Remove and replace unsuitable foundation Materials encountered at or below the foundation elevation using suitable replacement Materials as directed by the Engineer. Install the replacement Material in Lifts no greater than 6 inches thick, per 2106, “Excavation and Embankment – Compacted Volume Method.” Compact granular Materials used for bedding and foundation backfill in accordance with the Plans and 2106, “Excavation and Embankment – Compacted Volume Method.” D Backfilling and Compacting Excavations Backfill excavations for Structure construction to the required extent shown on the Plans and at the appropriate time. Uniformly distribute suitable Material meeting 1103 “Definitions: Select Grading Material,” in horizontal Layers throughout the excavation area in seams of no more than 6 inch compacted thickness. Compact backfill in accordance with 2106, “Excavation and Embankment – Compacted Volume Method.” If the Contract does not specify special backfill Materials, use Materials meeting 3149.2D.1, “Granular Backfill,” placed within 18 inches of the sides and 12 inches above the top of the Structure. For the remainder of the backfill, use embankment Material meeting 1103, “Definitions: Select Grading Material.” If outside the Roadbed construction, use suitable Material meeting 1103, “Definitions: Select Grading Material,” for the entire backfill. Do not place backfill Material on a frozen foundation or when the Material may freeze during the placement or compaction Work. Step the sides of the excavation if steeper than 4:1 and if potential wedging action of the backfill may be detrimental to the Structure. If the Contract does not require specific maximum dimensions for the excavation, the Contractor may enlarge the excavation and flatten the side slopes for convenience of backfill and compaction operations, at no additional cost to the Department. Maintain the sides of the excavation and prevent voids in the backfill when removing shoring or bracing from the excavation. E Surplus Materials Excavated Materials not used for backfill are the property of the Contractor. Dispose of surplus Materials in accordance with the disposal form submitted to and approved by the Engineer.

2451.4METHOD OF MEASUREMENT

The Engineer will determine quantities of excavation and embankment in accordance with 1901, “Measurement of Quantities,” except as modified by this section. Provide sufficient time for the Engineer to determine quantities. A Structure Excavation The Engineer will not adjust (P) designated quantities unless otherwise specified in 1901, “Measurement of Quantities,” or for excavation Materials reclassified by the Engineer. The Contractor may dispute an excavation quantity. If the Engineer considers the dispute, the Engineer will recalculate the excavation quantity for the entire Structure. If the Contractor completes the excavation before the Engineer directs a change, the Engineer will not make deductions or additions for resulting changes in the excavation volume if no enlargement of the excavation is required. The Engineer will consider additional quantities determined by recalculation as separate from the Contract Pay Item quantities for Structure excavation for Bridges.

The Engineer will measure rock within the Structure excavation and recalculate the volume for each excavation Pay Item classification considering the quantity of exposed rock measured . The Engineer will proportionately increase or decrease excavation Pay Item quantities based on the measured volume of rock to maintain the planned total excavation quantity. The Engineer will not adjust low water elevations as shown on the P lans or for safety concerns, working clearances, or stability of soils, regardless of existing conditions. The Engineer will calculate the volume of Structure excavation in accordance with the following limits except as modified for the type of Structure and unless otherwise required by the Contract:

limits of the Structure or its projections within the excavation

embankment or excavation, establishing the beginning of Structure excavation

The Department will consider the volume of removed Structures as a separate Contract Pay Item and will not include the volume of Structure removals within the excavation limits as part of the excavation volume. The Department will include the cost of Structure removals with other relevant Pay Items, unless otherwise required by the Contract. If the Plans include a separate Contract Pay Item for the removal of an existing Structure from the excavation limits of the new Structure, the Engineer will reduce the structural excavation quantity by the measured volume of the existing Structure. If the Contractor excavates Material to expedite the Work and the Contract includes the Material removal in a different Contract Item or indicates removal by others, the Engineer will not include this Material in the Structure excavation quantities. A.1 Cast-in-Place Structures For the horizontal limits of excavation for footings for cast -in-place Structures in ledge rock, the Engineer will use the footing limits as shown on the Plans. The Engineer will measure excavation for timber pile abutments and timber bents using the limits as shown on the Plans. A.2 Prefabricated Structures For foundation construction requiring a greater surface dimension than provided in 2451.4A, “Structure Excavation,” the Engineer will measure the excavation using the greater dimension. A.2.a Induced Trench For excavation by the induced trench method performed in accordance with 2501.3F, “Induced Trench Installation,” the Engineer will measure additional excavation required for loose backfill over the Structure in accordance with the following:

width of the Structure

B Granular Materials The Engineer will measure granular Materials for special backfill, bedding, or filter purposes by loose volume or compacted volume in accordance with 1901, “Measurement of Quantities,” and as required by the Contract.

2451.5BASIS OF PAYMENT

If the Contract does not contain a Contract Item for clearing or grubbing, the Department will consider clearing and grubbing to be Extra Work in accordance with 1402, “Contract Revisions.” The Department will pay for preliminary embankment construction in accordance with 2106, “Excavation and Embankment – Compacted Volume Method.” If the Contract does not include a Contract item for the restoration Work on the surface of the excavation site, the Department will include this cost with other relevant C ontract Pay Items. The Department will pay for cleaning and filling seams in rock foundations as E xtra Work in accordance with 1402, “Contract Revisions,” unless otherwise required by the Contract. The Contract Unit Price for the relevant Structure excavation and backfill Contract Items include the cost of disposing of surplus excavated Materials. For cast-in-place Structures, if the Plans do not include limits for the excavation of timber pile abutments and timber bents, the Department will include this cost with other relevant C ontract Items. If the Plans do not include a Contract Pay Item for Class R and Class WR excavation, the Department will pay for these Materials if encountered during Class E or Class WE excavation in accordance with Class R at 5 times the Contract Unit Price of Class E or Class WR at 3 times the Contract Unit Price of Class WE. Unless otherwise modified in the Contract, the Department will pay for the excavation for cast-in-place Structures in accordance with the following:

Unit Price by 25 percent for additional excavation to 3 feet below excavation as shown on the Plans. For excavation required to a depth greater than 3 feet below the planned elevation, the Department will pay for this portion of the additional excavation as E xtra Work in accordance with 1402, “Contract Revisions,” unless the Department and Contractor agree on a Unit Price increase not exceeding 25 percent.

Contractor objects to the Contract Unit Price, the Department will pay for the additional excavation as Extra Work in accordance with 1402, “Contract Revisions.”

excavation for Bridge Structure, and the recalculation shows an additional quantity, the Department will separately pay for additional Structure excavation for Bridge construction at 50 percent of the Contract Unit Price. The Contract cubic yard price for Granular backfill and Granular bedding will include the cost of placing and compacting the Materials. If the Plans do not include a separate Contract Pay Item for Structure excavation, the Department will include this cost with the Contract cubic yard price for Granular backfill and Granular bedding. If the Plans do not include specific Contract Pay Items, the Department will pay for granular Materials used for bedding, backfill, or filter purposes as shown on the Plans, in accordance with this section, and as directed by the Engineer as Extra work in accordance with 1402, “Contract Revisions.”

The Department will pay for structure excavation and backfill in accordance with the following schedule: Item No. Item Unit

2451.507 Structure Excavation Class ___ cubic yard

7 Granular Backfill (*) cubic yard

7 Aggregate Backfill (*) cubic yard

7 Granular Bedding (*) cubic yard

7 Coarse Filter Aggregate (*) cubic yard

7 Fine Filter Aggregate (*) cubic yard

7 Fine Aggregate Bedding (*) cubic yard

7 Coarse Aggregate Bedding (*) cubic yard

7 Conduit Aggregate Bedding (*) cubic yard

* Specify (LV) or (CV) in accordance with 2451.4B, “Granular Materials.”