206Excavation and Backfill for Culverts

Excavation and Backfill for Culverts

206.1DESCRIPTION

1 This section describes the requirements for the excavation, disposal of materials, and backfilling needed to install pipe culverts, structural plate pipe, box culverts, storm sewer systems, pipe siphons, water lines, sanitary sewer lines, and other conduits.

206.2MATERIALS

1 Provide materials in accordance with the following:

Materials

Admixtures Subsection

801.4 Bed Course Material 803.10 Flowable Fill 803.15 Fly Ash 801.2 Portland Cement 801.1 Water 814.1

206.3EQUIPMENT

1 Ensure that flowable fill equipment meets the requirements of Subsection 508.3, Equipment.

206.4CONSTRUCTION

206.4.1 Excavation

206.4.1.1 Culvert Excavation

1 Culvert excavation includes excavation for box culverts, pipe culverts, structural plate stock passes, or similar structures that require a uniform-width channel bottom and sloped sides. Vertical limits of culvert excavation are from the base of the bottom slab of box culverts or the bottom of the bedding limits to the top of the existing ground (the natural terrain surface in fill areas or the final subgrade line in cut areas). Longitudinal limits are 24 in [600 mm] beyond each end of the installation; the engineer may stake excavation beyond the longitudinal limits.

206.4.1.2 Trench Excavation

1 Trench excavation includes excavation for storm sewer systems, sanitary sewer lines, pipe siphons, water systems, utility lines, or similar installations where the contract

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specifies a trench with vertical sides. Vertical limits of trench excavation are from the base of the bottom slab of box culverts or the bottom of the bedding limits to the top of the existing ground (the natural terrain surface in fill areas and the final subgrade line in cut areas).

2 Excavate trenches to the specified line, grade, and width and with sides as nearly vertical as practical. When necessary, shore, sheet, and brace sides to prevent sliding or sloughing. Alternatively, the engineer may allow sloping of the trench walls above the top of the pipe being installed.

3 Excavate for manholes, inlet or outlet structures, and other structures associated with various types of conduit in the same manner as for conduit maintaining minimum clearances outside of each footing or wall as shown in the contract.

206.4.1.3 Culvert / Trench Subexcavation

1 The engineer may require additional excavation when unsuitable foundation conditions are encountered at the bottom of a channel or trench or when it is impractical to excavate to the established grade.

2 Excavation below the grade required to install pipe bed course material in the bedding limits, or the bottom of box culverts or other structures where no bedding is required will be classified as culvert subexcavation.

206.4.2 Disposal of Excavated Materials

1 Dispose of excavated material by one of the following methods:

2 Do not stockpile material for backfilling so that it interferes with construction or channel drainage. Transport excess material suitable for embankment construction to specified sites or as approved by the engineer. Waste and dispose of material unsuitable for use elsewhere on fill slopes or at specified locations. Do not place waste material next to a channel or on flood plain where flood waters can wash the material into a channel.

206.

4.3Protection of Structures

1 Protect excavations from saturation or erosion, and dewater sites where standing or running water would interfere with proper installation of the structure or pipes.

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206.4.4 Structure Foundation

1 For box culverts and other structures where bed course material is not specified, install the structure on undisturbed material. Where channels or trenches have been excavated below the established grade, place and compact backfill in loose layers approximately 8 in [200 mm] thick for the full length of the installation. Compact the last 6 in [150 mm] layer of material below the bottom of structures or bedding and other backfill material to at least 95.0 percent of maximum density and within plus 2 percent to minus 4 percent of optimum moisture content, in accordance with Subsection 203.4.3, Embankments and Cut Areas with Moisture and Density Control.

206.4.5 Backfilling

206.4.5.1 General

1 Place backfill in loose layers approximately 8 in [200 mm] thick. Compact each layer to at least 95.0 percent of maximum density and within plus 2 percent to minus 4 percent of optimum moisture content, in accordance with Subsection 203.4.3, Embankments and Cut Areas With Moisture and Density Control. For pipe culverts, use select bed course material within the limits specified and in accordance with Subsection 603.4.4, Pipe Bed Preparation, Subsection 603.4.5, Installing Pipe, and Subsection 603.4.9, Backfilling. Do not damage structures, culverts, or coating while backfilling and compacting. To avoid damage or lateral displacement, place and compact backfill layers equally on the sides of structures or culverts.

2 Do not place backfill against box culverts or other cast -in-place structures until the concrete has cured for 14 calendar days or test cylinders indicate an achieved compressive strength equal to at least 80.0 percent of design strength.

3 When placing bed course material and backfill below the spring line of a conduit, tamp or ram the material between the culvert and the channel bottom. 4 Place backfill over water and sanitary sewer lines by hand to an initial depth of 12 in [300 mm]. Do not drop material directly on pipe; place on both sides of the trench and allowed to flow over the pipe. Compact uniformly on both sides of the pipe to a height of approximately 12 in [300 mm] above the top of the pipe.

206. 4.5.2 Embankment Installations for Culverts

1 Install pipe culverts in accordance with the contract.

2 Construct embankment up to at least the springline elevation of the pipe and for no less than the minimum horizontal embankment limits measured perpendicular to the pipe prior to excavating the trench for the pipe installation. Springline is defined as the elevation of the maximum horizontal dimension of a culvert or conduit. For circular pipe it is one half the diameter above the invert.

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3 Construct embankment in accordance with Section 203, Excavation and Embankment.

206.4.5.3 Flowable Backfill

1 When specified, backfill culvert excavations to the depth and width specified and at least 12 in [300 mm] over the top of the conduit or structure with a flowable backfill.

2 Design the flowable backfill mix in accordance with T able 206.4.5-1, Flowable Fill Requirements.

3 When specified, backfill culvert excavations with flowable backfill to the depth and width specified and at least 12 in [300 mm] over the top of the conduit or structure.

4 Place flowable backfill in a manner as to prevent voids in, or segregation of, the material. Provide adequate restraints to resist hydrostatic forces and evenly place lifts on both sides of the pipe to prevent horizontal and vertical displacement. Ensur e visible free water is completely evaporated or removed prior to placing the next lift.

5 Allow flowable fill to set for a minimum of 24 hours prior to allowing vehicle loads to travel over the fill.

6 Remove foreign material prior to backfilling.

7 D eliver each load of flowable backfill with an accompanying department -furnished “Concrete Batch Ticket” (Form E-117) or with a computer generated ticket providing the same information.

8 Do not use flowable backfill within the bed course material limits.

Table 206.4.5-1 Flowable Fill Requirements Parameter Property or Limit Cement, minimum or Cement and fly ash, minimum 100 lbs/yd3 [60 kg/m3]

50 lbs cement/yd3 [30 kg/m3] and 80 lbs fly ash/yd3 [50 kg/m3] Water(1) estimated 50 gal/yd3 [250 L/m3] Aggregate estimated 3000 lbs/yd3 [1800 kg/m3] Air entraining admixture Optional Air content, maximum 15 percent Slump, minimum 6 in [150 mm] 20-day compressive strength, minimum 50 psi [345 kPa] 28-day compressive strength, maximum 100 psi [690 kPa]

segregation.

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206.5MEASUREMENT and PAYMENT

206.5.1 General

1 The engineer will measure:

based on the neat lines for the installation.

volume of Bed Course Material will be computed by using the minimum trench width, multiplied by the neat line for depth, multiplied by the neat line for length specified, less the volume of the pipe. The volume of flexible pipe will be based on the nominal inside diameter for round pipe or equivalent nominal inside diameter for arch pipe for the length specified. The volume of concrete pipe will be based on the nominal outside diameter for round pipe or equivalent nominal outside diameter for elliptical and arch pipe for the length specified. If flowable fill material is substituted, the same quantity of Bed Course Material as computed above will be used.

Backfill by the cubic yard [cubic meter] of material placed. The volume of Flowable Backfill will be computed by using the minimum trench width, multiplied by the neat line for depth, multiplied by the neat line for length specified, less the volume of the pipe. The volume of flexible pipe will be based on the nominal inside diameter for round pipe or equivalent nominal inside diameter for arch pipe for the length specified. The volume of concrete pipe will be based on the nominal outside diameter for round pipe or equivalent nominal outside diameter for elliptical and arch pipe for the length specified. The flowable backfill quantity cannot exceed the batch ticket quantity.

2 The department will pay as follows:

Pay Item

Pay Unit Measure to the Nearest Pay to the Nearest Culvert Subexcavation CY [m3] 0.1 ft [0.05 m] CY [m3] Bed Course Material CY [m3] 0.25 yd3 [0.25 m3] CY [m3] Flowable Backfill CY [m3] 0.25 yd3 [0.25 m3] CY [m3] Trench Subexcavation CY [m3] 0.1 ft [0.05 m] CY [m3]

206.5.2 Referenced Sections for Direct Payment

1 When specified, the engineer will measure and pay for:

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Excavation) as Unclassified Excavation, in accordance with Section 203, Excavation and Embankment.

ton [metric ton] or cubic yard [cubic meter] for the types of materials used, in accordance with the applicable sections of these standard specifications.