431401.03 SECTION 401—STRUCTURE EXCA V ATION
401.01 Description
This work shall consist of excavating and backfilling or disposing of material necessary for constructing substructures and superstructures of new bridges and altering existing bridges in accordance with these specifications and in conformity with the lines and grades shown on the plans or as established by the Engineer.
401.02 Materials
a.Earthen or other backfill shall conform to Section 303, be free of large or frozen lumps, wood, or rocks more than 3 inches in their greatest dimension, or other extraneous material unsuitable for construction, and shall be approved by the Engineer. Porous backfill shall conform to Section 204.02(c) or as specified herein.
b.Pipe underdrains shall conform to Section 232.02.
c.Select backfill material shall be No. 21A or 21B stone conforming to Section 208 or Select Material Type I, Min. CBR 30 conforming to Section 207.
d.Porous backfill shall consist of crusher run aggregate No. 25 or 26 conforming to Section 205.
e.Geocomposite Wall Drains shall conform to Section 245.
401.03 Procedures
Excavated material shall generally be used for backfilling and constructing embankments over and around the structure. The Contractor shall dispose of surplus or unsuitable material in a place and manner such that it will not affect or re-enter streams or otherwise impair the hydraulic efficiency or appearance of the structure or any part of the roadway. Where practicable, the Contractor shall construct substructures in open excavation and, where necessary, the excavation shall be sheeted, shored, braced, or protected by other means. If footings can be placed in the dry without the use of sheeting or cofferdams, forms may be omitted with the approval of the Engineer and the entire excavation filled with concrete to the required elevation of the top of the footing. The Engineer will not make adjustments for payment or excavation when forms are eliminated. Measurement and payment for structure excavation and concrete will be on a plan quantity basis. Unless tremie placement of concrete is specified, foundations for footings shall be kept free from standing or surface water until concrete and backfill operations have been completed. However, if the foundation is rock or the footing is supported on piles, other than for shelf abutments, dewatering need be performed only during concrete and backfill operations.
a.Preserving the Channel: Excavation shall not be performed outside caissons, cribs, cofferdams, or sheet piles. The natural streambed adjacent to the structure shall not be disturbed. The Contractor shall remove any material or obstructions deposited in the stream area because of the Contractor’ s operations. 432401.03 The Contractor shall submit a plan to the Engineer that shall include the specific locations of temporary structures or other obstructions that will constrict the stream flow and a description of construction activities that will contribute to constricting the stream flow prior to beginning work. The plan shall also include the dimensions and number of temporary structures and constrictions that are to be placed in the stream at any one time, and a dimensional elevation view of the stream and proposed temporary structures and constrictions.
b.Depths of Foundations: Elevations denoting the bottom of footings shown on the plans shall be considered approximate only. Foundations shall not be considered satisfactory until approved by the Engineer. The Contractor shall explore foundations by rod soundings or drillings to determine, to the Engineer’ s satisfaction, the adequacy for the foundations to support the structure. The Engineer will allow the Contractor to only make variations from plan depths to the foundations of open column abutments and solid or column piers by adjusting stem lengths if explorations indicate that satisfactory foundations can be obtained. The Contractor shall consider footing depths shown on the plans as minimum depths. Plan depths of concrete for footings may be increased not more than 24 inches at points of local irregularity over solid rock foundations. The Contractor shall only make variations from plan depths to foundations of solid or deep curtain-wall abutments by adjusting the depths of footings. The Contractor shall consider plan depths to be minimum depths, not to be exceeded by more than 3 feet. The Engineer shall be consulted for instructions for further action or redesign if explorations reveal that foundations or subfoundations are inadequate for the structure, or are not within the limits of permissible variation from the bottom of footing elevations as stated herein.
c.Preparing Foundations for Footings: The Contractor shall prepare hard foundation material so that it is free from loose material; clean; and cut to a firm surface that is either level, stepped, or serrated as directed by the Engineer. Seams shall be cleaned out and filled with concrete as directed by the Engineer. When concrete is to rest on an excavated surface other than rock, the bottom of the excavation shall not be disturbed. The Contractor shall not perform the final removal of foundation material to grade until just prior to concrete placement. When the elevation of the bottom of a footing is above the level of the original ground, the Contractor shall not place the footing until the approach embankment has been placed and compacted to the elevation of the top of the footing and excavation has then been performed through the embankment to the elevation of the bottom of the footing. When a footing is to be placed over material subject to movement because of pressure from overlying or adjacent fill, the footing or piles for the footing shall not be placed until after the fill has been placed and compacted. Excavation for shelf abutment footings shall be limited to a perimeter extending not more than 18 inches outside the neat lines at the bottom of the footing. If the Engineer determines the material on which a foundation is to be placed using piles is unsat - isfactory, the Contractor shall undercut the originally proposed excavation a depth of 6 to 12 inches as directed by the Engineer and backfill that area with crusher run aggregate, select borrow, or other material approved by the Engineer. 433401.03
d.Holes for Drilled-In Caissons: Foundation bearing areas shall be cut to an approximately level surface except that they may be stepped or serrated on hard rock. If material is encountered that is not sufficiently cohesive to maintain the proper diameter of the hole, casing shall be used.
e.Cofferdams: Cofferdams for foundation construction shall be as watertight as practicable and carried to a depth that will allow them to function properly without displacement. The interior dimensions of cofferdams shall be such as to give sufficient clearance for the construction of forms and inspection of their exteriors and permit pumping from outside the forms. Cofferdams that are tilted or moved laterally during sinking shall be realigned to provide the required clearance. If conditions are encountered that make it impracticable to dewater the foundation, the Engineer may require the Contractor to construct a concrete foundation seal of the dimensions necessary to ensure that the balance of the concrete can be placed in the dry. The Contractor shall provide anchorage, such as dowels or keys, to transfer the entire weight of the cofferdam into the foundation seal when weighted cofferdams are employed and the weight is used to overcome the hydrostatic pressure acting against the bottom of the foundation seal. Cofferdams that are to remain in place shall be ported at the low water level. The Contractor shall construct cofferdams in a manner to prevent damage to fresh concrete from a sudden rising of the stream and prevent damage to the foundation by erosion. Timber or bracing left in cofferdams shall not extend into the substructure concrete. The Contractor shall remove cofferdams, including sheeting and bracing, in a manner that will not disturb or damage the finished concrete after completion of the substructure.
f.Pumping: The Contractor shall execute pumping from the interior of a foundation enclosure in a manner as to preclude the possibility of water moving through any fresh concrete. The Engineer will not permit pumping during concrete placement or for at least 24 hours thereafter unless it is performed from a suitable sump separated from the concrete work.
g.Protecting Existing Structures or Utilities: When foundations are located such that excavation may endanger or interfere with an existing structure or utility, the location of bracing and method of protection shall be subject to approval by the owner of the structure or utility.
h.Inspection: The Contractor shall notify the Engineer and request his inspection and approval after each excavation has been completed. The Contractor will not be permitted to place concrete until the Engineer has approved the depth of the excavation and the character of the foundation material.
i.Backfilling: Excavated spaces that are not occupied by wingwalls, abutments, piers, or other permanent work not specifically addressed herein shall be backfilled with soil to the surface of the surrounding ground. The Contractor shall use select backfill material behind all abutments. The Department will include a detail indicating the limits (zone) of the select backfill in the Plans. The Contractor shall compact the material in accordance with Sections 305 and 303 respectively. The top surface of the backfill material shall be neatly graded. The earthen fill around the perimeter of the select material zone in abutments, wingwalls, and retaining walls shall be placed in horizontal layers not more than 6 inches in loose thickness and then compacted at ± 20 percent of optimum moisture to a density of at least 95 percent as compared to the theoretical maximum density as defined in Section 101.02. The Contractor shall perform tests 434401.03 to verify compliance with density requirements in accordance with VTM-12. The Contractor shall place and compact the backfill in front of units in horizontal layers to the same elevation as the layers behind units until the final elevation in front is reached as the work progresses. Backfill in front of units shall be placed and compacted in horizontal layers to the same elevation as the layers behind units until the final elevation in front is reached. Backfill shall be placed in a manner to prevent wedging action against the concrete. The Contractor shall modify slopes bounding excavation for abutments, wingwalls, or retaining walls to lock in adjacent backfill material by stepping or serrating the existing soils. The Engineer will not permit jetting of the fill behind abutments, wingwalls, or retaining walls. Fills and backfills around piers not included in the roadway prism shall be constructed in uniformly compacted layers and placed alternately to maintain a uniform elevation on both sides of the structure. However, the Engineer will not require the Contractor to achieve the density requirement for acceptable compaction. The Contractor shall make provisions for the draining of backfill material. Geocomposite wall drains shall be used to drain the select backfill material in all abutments. Porous backfill shall be used in to drain backfill material in retaining structures unless otherwise stated on the plans. If the Contractor requests the Engineer’ s approval to substitute geocomposite wall drain in lieu of porous backfill in a retaining structure, and the Engineer approves such a request, the geocomposite wall drain shall be provided at no additional cost. Geocomposite wall drains shall be installed in accordance with the manufacturer’ s recommenda - tions. The Contractor shall provide a minimum three (3) inch joint overlap of geotextile fabric at the top, bottom, ends, and at adjoining panels. The geocomposite wall drain shall be connected to an outlet drain pipe or weep hole at least 6 inches in diameter. The outlet drain shall be completely wrapped by the bottom fabric flap of the geocomposite wall drain. The Contractor shall provide a detailed sketch of the proposed outlet drain pipe connection as well as connections to any special drainage systems associated with the structure for the Engineer’ s approval prior to installation. Porous backfill for draining backfill material behind retaining structures shall consist of crusher run aggregate, conforming to Section 205 unless stated otherwise on the plans. The Contractor shall place porous backfill at the back of weep holes to extend 18 inches behind the entrance to the hole, 18 inches above the elevation of the bottom of the hole, and 18 inches laterally on each side of the centerline of the hole. If crushed glass is used as porous backfill, No. 78 and/or No. 8 aggregate and an 18-inch by 18- inch swatch of drainage fabric conforming to Section 245.03(c) shall be used to cover the #4 mesh at each weep hole opening exposed directly to crushed glass, or as otherwise approved by the Engineer. The Contractor will not be permitted to place backfill against abutments or wingwalls until concrete has been in place at least 14 days, exclusive of days on which the average high-low air temperature is below 40 degrees F in the shade or until test cylinders have attained a compressive strength equal to 93 percent of the required 28-day design minimum compressive strength. The exception to this requirement is in cases where completion of grading in the area in front of an abutment is desired. In those circumstances, backfill and/or fill may be placed against abutments or wingwalls to a point no higher than the elevation necessary to complete grading in front of the abutment, provided:
1.The concrete has been in place at least 7 days, exclusive of days on which the average high-low air temperature is below 40 degrees F in the shade, or
2.Test cylinders have attained a design minimum compressive strength greater than or equal to 900 psi and the concrete has been in place a minimum of 2 days, exclusive of days on which 435401.04 the average high-low air temperature is below 40 degrees F in the shade. The Contractor shall take additional cylinders at the time of concrete placement and use a calibrated machine or an independent lab to test the cylinders and verify the design minimum compressive strength requirement has been met prior to backfilling. Backfill shall be placed as soon as practicable following attainment of the required design minimum compressive strength but not later than 30 days after concrete placement. Excavation openings shall be maintained as dry as practicable at the time of backfilling. The Contractor shall place backfill in a manner to deter impoundment of water and facilitate existing drainage.
j.Filled Spandrel Arches: Fill for spandrel arches within 1 1/2 times the height of the arch shall be placed in a manner to load the ring uniformly and symmetrically. Fill material shall be homogeneous soil and shall be placed in horizontal layers not more than 6 inches in loose thickness, compacted in accordance with Section 303.04(h), and brought up simultaneously from both haunches. The Engineer will not allow the placing of wedge-shaped sections of fill material against spandrels, wings, or abutments.
k.Approach Embankment: Approach embankment shall be constructed in accordance with Section 303.04(h).
401.04 Measurement and Payment
Structure excavation will be measured in cubic yards of material removed from within the limits of vertical planes 18 inches outside the neat lines of footings or within vertical planes 18 inches outside of neat work that does not have footings directly beneath it, such as in cases of curtain walls or cantilevered wingwalls. Structure excavation will be measured from the surface of the original ground or approach roadway down to the bottom of the foundation shown on the plans or such foundation as the Engineer may approve, down to 18 inches below the bottom of the neat work not directly over footings, or to the top of existing concrete where excavation is to permit placing new concrete over existing concrete. When specified on the plans, structure excavation will include material removed outside the limits specified for the substructure and to a depth of 18 inches below the lowest beam or bottom of the slab of the superstructure or to such depth as shown on the plans. The width of such excavation will be limited to 18 inches outside the exterior beams or edges of the slab or as shown on the plans. Excavation above the bottom of a proposed channel change or roadway template or an overpass road will not be included as structure excavation. Structure excavation will be paid for at the contract unit price per cubic yard. This price shall include clearing and grubbing, sheeting, shoring, bracing, placing and compacting backfill, dewatering, furnishing and placing aggregate for weep holes, disposing of unsuitable or surplus material, and clearing the channel of obstructions caused by construction operations. Excavation for drilled-in caissons will be measured in linear feet of drilled hole from the existing ground to the bottom of the finished hole as measured along the centerline of the hole and will be paid for at the contract unit price per linear foot. This price shall include drilling, underreaming, furnishing and installing casing, and preparing the hole. Furnishing and placing backfill will be included in the price for structure excavation and will not be measured for separate payment unless specific material is required by the Engineer and no suitable 436401.04 material is available within the construction limits. When specific material is required for backfill by the Engineer, measurement and payment will be in accordance with Section 104.03. Porous backfill, when a pay item, will be measured in cubic yards of material within the limits shown on the plans or as otherwise directed by the Engineer and will be paid for at the contract unit price per cubic yard. Pipe underdrains, when a pay item, will be measured in linear feet and will be paid for at the contract unit price per linear foot for the size specified. Unsuitable materials removed below the plan foundation will be measured and paid for as structure excavation. Foundation seals required by the Engineer and that are properly placed for structural adequacy as a part of the planned footing will be accepted as part of the permanent footing. Measurement and payment will be in accordance with Section 404.08. Foundation seals that are not required by the Engineer shall be included in the price for structure excavation. Clearing and grubbing within the area defined by lines connecting the extremities of the substruc - ture units, regardless of whether excavation is involved, shall be included in the price for structure excavation unless otherwise specified in the Contract. Cofferdams will be measured in units of each per foundation and will be paid for at the contract unit price per each. This price shall include furnishing, erecting, maintaining, and removing when no longer necessary. Select backfill (Abutment zone) will be measured in tons and paid for at the Contract ton price. This price shall include furnishing, placing, compacting, and grading select backfill material. Geocomposite Wall Drain will be measured in square yards and will be paid for at the contract unit price per square yard. This price shall include furnishing and placing the wall drain. Overlaps will not be measured for payment. Payment will be made under: ————————————————————————Pay Item Pay Unit————————————————————————Structure excavation Cubic yard Drilled holes Linear foot Porous backfill Cubic yard Pipe underdrain (Size) Linear foot Cofferdams Each Select Backfill (Abutment Zone) Ton Geocomposite Wall Drain Square Y ard———————————————————————— 437403.04 SECTION 402—SHEET PILES
402.01 Description
This work shall consist of furnishing and installing the type of sheet piles shown on the plans or specified by the Engineer to be removed, or to be left in place as part of the finished structure.
402.02 Materials
a.Timber sheet piles shall conform to Section 236 and may be of any species of wood that can be driven satisfactorily. Piles shall be free from worm holes, loose knots, wind shakes, decayed or unsound portions, or other defects that might impair their strength or tightness.
b.Concrete and reinforcing steel for concrete sheet piles shall conform to Sections 217 and 223, respectively.
c.Steel sheet piles shall conform to Section 228.
402.03 Procedures
a.Timber Sheet Piles: The Contractor shall furnish piles that are sawed with square corners and provided with tongues and grooves of ample proportions, either cut from the solid material or made with three planks securely fastened together. Piles shall be drift sharpened at the lower ends to wedge the adjacent piles tightly together. The top of piles shall be cut off to a straight line. Piles shall be braced with waling strips that are lapped and joined at splices and corners. Wales shall be in one length between corners and bolted near the top of the piles.
b.Concrete Sheet Piles: Concrete sheet piles shall be manufactured in accordance with Section 403, 404, or 405, as applicable. The Contractor shall install concrete sheet piles in accordance with Section 403.
c.Steel Sheet Piles: When assembled in place, pile sections shall be practically watertight at the joints. Painting of steel sheet piles shall be performed in accordance with Section 403. Piles shall be provided with tongues and grooves of ample proportions for securely fastening together. Wales and structural supports shall be provided as necessary to ensure structural integrity.
d.Temporary Sheet Piling: When shown on the plans or directed by the Engineer, temporary sheet piling will be measured in square feet. The Engineer will measure the horizontal dimensions contin - uously along the outer face of the sheet piling. The bottom limit will be the bottom of the excavation shown on the plans or authorized by the Engineer. The top limit will be the original ground line or, in areas adjacent to traffic, 3 feet above the original ground line, or as otherwise shown on the plans.
402.04 Measurement and Payment
Sheet piles will be measured in square feet of piles remaining in place and will be paid for at the contract unit price per square foot. The Engineer will measure the horizontal dimensions continuously along the
Source: Virginia Road and Bridge Specifications, 2020 Edition. Pages 459–464 of 1,065.