401 - Culverts

401 Pipe Culverts

GENERAL DESCRIPTION

Definitions of Terms

Curb and Gutter: Curb and gutter is the edge of the paved roadway that collects water and is designed to drain to a catch basins, downspouts, and spillways.

Detention Pond: A detention pond is a temporary storage area that is engineered to control storm water. Excess storm water is collected within a detention pond during heavy rain events to help mitigate flooding and erosion downstream. A detention pond typically dries out between rain events.

Outfall: An outfall is the outlet where a culvert discharges storm water to a body of water or basin.

Retention Pond: A retention pond is a permanent storage area for excess storm water runoff. Excess storm water is collected in the retention pond, aiding in the control of erosion. Often, there is a weir or another filtration system within the retention pond, which is used to filter the storm water as it travels through the pond. Retention ponds can serve as artificial wetlands for the surrounding area, increasing biodiversity.

Runoff: Runoff is drainage that leaves an area as surface flow and enters a culvert, typically through a ditch.

Sedimentation: Sedimentation is the process of depositing soils that were eroded by the flow of water.

Watershed: A watershed is an area of land that drains to a specific point.

General Overview

Pipe culverts are used to convey water under roadways, railways, etc. Culvert construction consists of installing culverts of the size and class required, including excavation, bedding, backfill, and compaction of the backfill material. Refer to Section 401 of the Standard Specifications for Construction for culvert information.

The key components of culvert systems include:

1. Inlet: Inlets are typically end sections or headwalls to permit water to enter into the system.
2. Pipe: Pipe is the conduit responsible for transporting water to the outlet. Project documents specify the size and material of the pipes.
3. Outlet: Outlets are typically end sections or headwalls which discharges water to a ditch, a body of water, or a basin.

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MATERIALS

All materials must meet acceptance requirements in the Materials Source Guide and be listed on the Contractor-provided Material Source Lists in the project files.

Description of Materials

The pipe material and class are noted on the plans. MDOT defines the pipe by class, which is based on the amount of cover over the pipe. Refer to Table 401-1 of the Standard Specifications for Construction for acceptable pipe in each class.

Parts of a Pipe

Culvert materials include:

• Plastic:
  • Smooth-lined corrugated polypropylene pipe (PPP). Grey in color.
  • Smooth-lined corrugated polyethylene pipe (CPE) Type S. Black in color.
  • Corrugated polyethylene pipe (CPE) Type C. Black in color.
  • Corrugated polyvinylchloride pipe (CPV). White in color.
• Concrete:
  • Reinforced concrete pipe (RCP).
  • Non-reinforced concrete pipe.
• Metal:
  • Corrugated metal pipe (CMP).
  • Corrugated and spiral ribbed pipe (CSP).

Each culvert section, regardless of type, must be clearly marked with the following information:

• Pipe class and specification designation (ASTM or AASHTO).
• Date of manufacture.
• Name or trademark of the manufacturer.
• Plant identification.

The marking is either painted on the inside or scribed on outside of concrete pipes, and is painted on the outside of metal and plastic pipe.

Pipe Identification Markings

Concrete Sewer Pipe Manufacturer Classification

To aid in the joining of pipe segments and to seal the pipe so the joints do not leak, lubricant and gaskets are used.

Example of Pipe Gasket Seal Lubricant

Concrete Sewer Pipe with Rubber Gasket

Any culvert pipe found with defects (cracks, fractures, exposed rebar, deformities, etc.) prior to or during installation are to be rejected and removed from the project site. Any damage caused by the Contractor’s operation to existing culverts that are intended to be salvaged must be removed and replaced with similar material without damage or defects at no cost to the contract.

Plastic Pipe (PPP, CPE and CPV)

Plastic pipe is more susceptible to shipping and storage deformation than concrete or metal pipe. Improper lifting and storage can lead to misshapen sections that are difficult to lay at a proper grade if the curve is placed vertically, and difficult to lay at a proper alignment if the curve is laid horizontally. Plastic pipe should not be deformed (out-of-round) or have blemishes in the extrusion. It should not have gouges or tears on the exterior, the interior, or the bell ends. Plastic pipes should have protective gaskets installed on the spigot ends. Gaskets should be clean and not dried out during installation.

Concrete Pipe

Concrete pipe is precast by a manufacturer and is made of cementitious materials, aggregates, and in most cases steel reinforcement.

Concrete pipe and end sections must not be cracked or chipped, especially on the bells and spigots that are to make durable watertight joints. The concrete used must be free of segregation and honeycombing. If RCP is used, the internal reinforcement steel must not be visible on the exterior.

Metal Pipe (CMP and CSP)

Corrugated metal pipe should not be out-of-round, exhibit deviation from a straight alignment, or have dents or bends in the metal that can create loose, poorly formed joints. Bruised or broken zinc, aluminum, or polymer coating must be repaired by the Contractor in accordance with the manufacturer’s specifications at no cost to the contract.

Damaged Polymer-Coated CSP

Headwalls and End Sections

Headwalls are typically made of precast or cast-in-place reinforced concrete. Any headwall or end section with cracks or chips which were caused during shipment or placement must not be accepted. The finished concrete surface must be free of segregation and honeycombing, and the reinforcement steel must not be exposed.

Concrete Headwall

Concrete End Section

End sections should be manufactured with the same material as the pipe. Exceptions are for plastic pipe, which may use either metal or concrete end sections, and for metal sloped end sections, which can be placed on concrete or CMP. Concrete end sections must have the footing cast-in-place or precast in accordance with the Standard Plan R-86 series. Metal end sections cannot be dented or misshapen, and the connecting hardware must be for the correct pipe size. All struts and bolts for the end sections must be used, and the proper end section, longitudinal or transverse, must meet the plan application. Toe plate extenders must be included on all metal end sections. The metal end section and all hardware to connect the metal end section must be galvanized.

Metal Sloped End Section

When discharging directly to waters of the state, a permanent outfall label is required. The label should identify MDOT in a visible manner. Refer to Subsection 401.03.E of the Standard Specifications for Construction and the Standard Plan R-85 series, R-86 series, R-88 series, and R-95 series for additional details on outfall label instructions. If an outfall discharges to a ditch, it does not need to be labelled.

Bedding and Backfill

Bedding material is comprised of granular material Class IIIA, or Michigan Series 34R if undercuts are required. The material used is determined by the existing subgrade material at the bottom of the trench.

Backfill material varies depending on what is above the pipe culvert being installed and the type of pipe that is used. Typical backfill consists of granular Class II, IIAA, III, or IIIA material, suitable excavated material, or a concrete encasement. Refer to the Standard Plan R-83 series for details.

34R Aggregate

46G Aggregate

Class II Sand

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EQUIPMENT

The following equipment can be used for pipe culvert work:

• Excavator
• Backhoe
• Front end loader
• Trench box
• Occasionally, a bulldozer and a vibratory roller for aggregate compaction
• Plate compactor
• Ho-Pac attachment
• Gas powered rammer tamping machine
• Air powered pogo thumper hammer
• Sand/stone box
• Portable concrete mixer
• Cement/mortar mixing tub
• Portable generator
• Electric submersible pump
• Trash pump
• Pipe laser with target
• Transit or laser level
• Leveling/grade pole
• Electric impact wrench
• Pipe/spud bar
• Small hand tools (shovel, level, pipe “cutoff” saw, etc.)

Description of Equipment

Typically, an excavator is used to remove existing culverts and dig the trench for new culverts. A laser or other acceptable alignment device is used to install the culvert pipe to proper grade as it is laid in the trench by the excavator. A front-end loader or excavator is used to place backfill around the pipe to be compacted in layers by a Ho-Pac or other compaction equipment. In some cases, with a large trench, a truck will dump the backfill material directly into the trench to be graded by a bulldozer before compaction.

Pictures of Equipment

Excavator with Plate Compactor Attachment (Ho-Pac)	Pipe Laser	Bulldozer
Laser Transit	Portable Concrete Mixer	Plate Compactor
Jumping Jack Compactor	Cutoff Saws

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PRECONSTRUCTION

Prior to the start of construction, the Inspector should perform the following:

1. Inspect the pipe upon arrival to site.
   • Verify the pipe meets the requirements contained in the plans, specifications, and any addenda.
     • The pipe must be accompanied by the manufacturer’s certification, tested stock reports, or other requirements as specified in the Materials Quality Assurance Procedures Manual.
     • Review the cover over the top of the pipe as called for in the plans and verify against the pipe chart (Table 401-1 of the Standard Specifications for Construction) for acceptable pipe installation depth and class.
   • Visually inspect the pipe for defects originating from the manufacturing process or occurring during delivery and unloading at the site (such as cracks, fractures, exposed rebar, deformities, etc.). Any damaged pipe should be promptly rejected by the Engineer.
     • Inspect the bell and spigot end of the pipe to ensure there are no chips or cracks that might impede a watertight joint connection.
     • Inspect plastic culvert pipe to ensure it does not exhibit deformities that would hinder water flow.
     • Using survey paint, mark any rejected pipe with an “R” to indicate rejection of the pipe. It is good practice to mark both the inside and outside of the pipe.
2. Verify the survey stakes are placed according to the plans and the appropriate invert elevations, rim elevations, and pipe and structure IDs are labeled on the stakes.
   • Ensure proper offset stakes are placed as stakes placed in the location of the proposed culvert will be removed when excavation begins.
3. Verify existing underground utility markings.
   • Take note of any potential utility crossings and reference the plans and profiles to ensure minimum clearances are met.
4. Review the plans and the Special Provision for Maintenance of Traffic. There may be restrictions or staging requirements for installation of the culvert. Installation restrictions are typically associated with staging requirements on a project and access to side streets and driveways.
5. Hold an onsite meeting with the Contractor to discuss:
   • The construction methods that will be used to complete the work.
   • Required traffic control measures, proximity of traffic to the work area, and maintaining driveways during construction.
   • Communication required if impacting residents or businesses during installation.
     • Residents and businesses should be contacted if there will be disruptions to services. Coordination by the Contractor with impacted users may be required if disruption is necessary.
   • Review local ordinances.
   • Disposal of excavated material and material stockpile locations. The Contractor should provide authorization letters to the Engineer noting material stockpile and disposal locations.
   • Soil erosion and sedimentation control measures that will be utilized to minimize soil erosion and subsequent sedimentation.
   • Methods for securing the site during work operations and at the end of each workday.
     • Including maintaining appropriate cover over the top of the pipe to minimize damage to the pipe from construction traffic.

If offset stakes are used, a review of the offset staking in the field should conducted to verify the correct station location has been set, and whether the end of the culvert, or the culvert end sections, have been staked. This difference will determine the position of the culvert compared to the ditches and the foreslopes for transverse applications and crossroad of driveway slope widths for longitudinal culverts. Making a measurement between the offset stakes end-to-end should determine whether the culvert pipe length has been staked, with the end sections placed beyond the offsets, or if the offsets are to the ends of the end sections.

Example: Culvert length = 100’ End Section = 6’ long If the measurement between the two respective offsets is ~112’, the offsets are to the limits of the end sections (6+100+6 = 112). If the measurement between the two offsets is ~100’, the Inspector should determine if the additional 6’ of End Section will “fit” the ditches and the slopes. The material of the culvert should be taken into consideration. Concrete pipe “lays” 8.2’, while ductile iron pipe lays 18’, and PVC and HDPE pipe lay 20’. Only the 20’ foot length will fit the planned 100’ length in the culvert. The concrete pipe (100/8.2 = 12.2 pipe lengths) will end up ~1.5’ short overall by laying 12 pipe lengths. The ductile iron pipe would require cutting a pipe in half at one end or the other (100/18 = 5.6 pipe lengths). These calculations are estimates, because the actual laying of pipe will vary depending on how well the joints are made. A little “pipe creep” is not unusual.

A review of the proposed culvert depth on the profile sheets should be compared to all known existing utilities that will be crossed, and any other proposed utilities and structures to be built, with attention paid to elevation conflicts. The size of the culvert must be considered. The plan invert elevation might not be in conflict, but the height of the pipe above the invert might be. Likewise, an elevation shot on “top” of an existing utility needs to consider the size of the utility below the top.

Example: The proposed invert of a 12” concrete pipe is 100.00 at the outlet and 100.50 at the inlet. The culvert is 100’ long. A 6” gas main exists at the middle of the run (50’ out) with a top-of-pipe elevation of 101.50. 101.5 - 0.5’ = 101.00 at the bottom of the gas pipe. Calculate the pipe grade using rise/run. 0.5’ rise/100’ run = 0.005’ rise per foot. 0.005 x 50’ = 0.25 rise to the point where the gas main crosses. Invert 100.00 + 0.25 = 100.25 at 50’ out + 12” (pipe size), + 0.25 pipe thickness = 101.50 at the top of the culvert 50’ out. There is an elevation conflict between the proposed 12” culvert and the existing 6” gas main. Example Drawing of Anticipated Utility Conflict

The plan sheets should also be examined for alignment conflicts. These kinds of conflicts are not as common with culverts as they are with other pipe utilities because of the generally shorter lengths of culverts, but they can happen.

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CONSTRUCTION

Trench Excavation

Construction of a culvert begins with trench excavation. Excavation may also include the removal of an existing culvert, end sections, footings, or headwalls. These removal quantities should be recorded as called for in the specifications.

Trench Box and Steel Plates being used for Culvert Construction

There are many factors that determine the safe and proper width of a pipe trench. Refer to OSHA Regulation 1926, Subpart P, Excavations, for all applicable sloping, shoring, and soil classification safety standards for excavation. Existing soil material, groundwater elevation, utilities, trees (roots), and proximity of paved surfaces (roads, sidewalks, and curbs and gutters) and buildings may all be considered by the Contractor when deciding how the trench will be excavated.

In accordance with Subpart P, soil can be classified as 3 different types:

1. Type A: A cohesive soil with unconfined compressive strength of 1.5 ton per square foot (tsf) or greater. Examples include clay, silty clay, sandy clay, clay loam, and in some cases silty clay loan and sandy clay loam. Cemented soils like caliche and hardpan are also considered Type A soils. However, the soil cannot be classified as Type A if one or more of the following conditions are met:
   • The soil is fissured.
   • The soil is subject to vibration from heavy traffic, pile driving, or similar effects.
   • The soil has been previously disturbed.
   • The soil is part of a sloped, layered system where the layers dip into the excavation on a slope of 4H:1V or greater.
   • The material is subject to factors that would require it to be classified as a less stable material.
2. Type B: A cohesive soil with unconfined compressive strength greater than 0.5 tsf but less than 1.5 tsf. Granular cohesionless soils include angular gravel (crushed rock), silt, silt loam, sandy loam, and in some cases silty clay loam and sandy clay loam. Other characteristics include:
   • Previously disturbed soils except those which would otherwise be classified as Type C.
   • Soil that meets the compressive strength or cementation requirements for Type A but is fissured or subject to vibration.
   • Dry rock that is not stable.
   • Material that is part of a sloped, layered system where the layers dip into the excavation on a slope less steep than 4H:1V, but only if the material would be otherwise classified as Type B.
3. Type C: A cohesive soil with an unconfined compressive strength less than 0.5 tsf. Examples include gravel, sand, and loamy sand. Other characteristics include:
   • Submerged soil or soil from which water is freely seeping.
   • Submerged rock that is not stable.
   • Material in a sloped, layered system where the layers dip into the excavation on a slope of 4H:1V or steeper.

Following are various sloping requirements in accordance with OSHA regulations.

Sloping Requirements by Soil Type	Maximum Allowable Slope with Support System by Soil Type
Maximum Allowable Slope with Support System by Soil Type	Maximum Allowable Slopes by Soil Type

The width of the trench should be sufficient to enable a worker to place and compact material under the pipe haunches. The Standard Plan R-83 series provides direction for minimum trench width as a function of the pipe size.

Trench boxes and/or sheeting can be used to “steepen” the banks of a trench. By limiting the width of the trench, the Contractor can minimize excavation and backfill quantities and avoid conflicts with existing utilities, tree roots, and removal of more pavements than otherwise necessary. Some sheeting systems or cofferdams require “engineering” due to depth of material retained. Refer to Subsection 704.03.A of the Standard Specifications for Construction, which describes the design for sheeting and cofferdams for retaining soil in a trench greater than 6 feet deep.

The trench must be excavated and graded to the proper alignment and grade, leaving room for at least 4 inches of granular material as a bedding layer below the pipe. The bedding material must be graded uncompacted uniformly so the entire length of the pipe is firmly supported. If the pipe has bells that are larger in diameter than the barrel of the pipe, the surface of the bedding at the location of the bell can be lowered, so the bell is not propped up creating a void beneath the barrel or a misalignment of the pipe. The Contractor should not adjust the grade of the as-placed pipe in the trench with an excavator or other equipment.

Where rock or unyielding hardpan is encountered in the culvert trench, it should be excavated to a minimum of 6 inches below the proposed bottom of the pipe, backfilled with granular material Class IIIA, and compacted. The Standard Plan R-82 series provides details for bedding and filling around pipe culverts in various applications and should be strictly followed. Backfill should be thoroughly compacted under the haunches of the pipe to provide uniform bearing throughout.

Dewatering

Dewatering of the trench may be required if either the groundwater elevation or water in the existing ditches is inundating the trench bottom. If pumps are employed to control the water, proper soil erosion and sedimentation control should be employed as well. Running the discharge of a pump through a filter bag is a common requirement. In some cases, multiple filter bags may be required. Direct discharge of pumped water to a watercourse is prohibited.

Undercutting

Undercutting the proposed trench bottom may be required if the material in the bottom is unstable and will not sufficiently support the pipe. Trench undercutting has a separate pay item (Trench Undercut and Backfill) that must be calculated by the cubic yard. Refer to Subsection 401.03 A and Subsection 402.04.E of the Standard Specifications for Construction for construction details and method of payment, respectively. The additional depth below the intended trench bottom must be backfilled with Michigan Series 6A, 17A, or 46G aggregate. Granular material (Class I, II, or III) and other “suitable material” are not acceptable and not included in the pay item.

Bedding

Culverts should be placed on suitable bedding material. Soft or spongy materials do not provide a firm bed for the pipe culvert. Excavation and bedding for culverts must be in accordance with Section 401.03 of the Standard Specifications for Construction. Culvert bedding must be prepared in accordance with the details in the Standard Plan R-82 series.

Pipe Placement

Pipe laying typically begins at the outlet end and proceeds uphill with the bells on the higher end. Sometimes culverts must be laid backwards from the inlet end downhill. In this case, the pipe bells should still be laid to the higher end of the individual pipe sections.

The first piece of pipe laid should be set to the plan invert elevation and reasonably at the plan grade. Typically, a pipe laser is used to control the alignment and the grade by directing the beam at a target placed in the pipe. The plan grade is entered into the pipe laser and the laser is directed in the plan alignment of the culvert by sighting the centerline of the opposite end where the target is placed, which is measured from the offset stakes. By checking the invert elevation of the first pipe with the “cut/fill” of the offset stakes and checking the invert elevation (rise/run) periodically throughout the pipe laying operation, the Inspector will know if the plan elevations are being maintained.

The Contractor should not use the backhoe bucket or other excavation equipment to adjust the grade of the pipe. If the grade needs to be increased or decreased, the end of the pipe should be lifted to remove excess material or add additional material. Using the backhoe bucket or other excavation equipment to adjust the grade will damage the pipe.

The Inspector should verify the pipe sections are pushed home completely during installation. Ensure the Contractor does not forcefully slam the pipe connections together.

Prior to backfilling, all pipe joints must be wrapped with a non-woven geotextile blanket. The fabric must have a minimum width of 36 inches, be centered on the joint, and overlap on the ends by at least 12 inches.

The joints of CMP are different than the description above because there are no bells and spigots. The ends of the pipe sections are joined using couplers made of an open steel band that is passed around the joint and then secured together with a bolted connection. To make the joint watertight, a gasket must be placed around the pipe between the coupler and the pipe. After the bolt(s) have been tightened on the coupler, the joint is wrapped, as described above, with geotextile blanket.

Joint Types of CMP Pipe

Elliptical concrete pipe should be installed with the lift holes on the top of the pipe. The manufacturer’s marks designating the top and bottom of the pipe should not be more than 5 degrees from the vertical plane through the longitudinal axis of the pipe. After installation, the lift holes should be sealed with suitable concrete plugs and waterproofed.

Watertight Joints

All pipe joint assemblies for use in culverts must be selected from the Qualified Products List.

Proper installation of the required rubber gaskets is crucial for performance and joint integrity of every RCP pipe segment and manhole. Equalization of each gasket, as well as proper utilization of the supplier-furnished/approved joint lubricant on the pipe joints, is necessary. The o-ring stretch can be equalized by running a smooth, round object (inserted between gasket and spigot) around the entire circumference three times. Installation methods may vary depending on the pipe/manhole supplier. Following are installation procedures for two common types of gaskets.

Installation Procedure for O-Ring Gasket (Source: Press-Seal Corporation)

Installation Procedure for Type 4 Gaskets (Source: Press-Seal Corporation)

Backfilling

Backfilling around the culvert must be completed in accordance with the Standard Plan R-82 series and R-83 series. The Contractor should place backfill equally on both sides of the pipe in layers no greater than 10 inches. The material of the culvert and what is proposed to be constructed above the culvert will dictate what materials are acceptable for use when backfilling.

Example: A concrete culvert that extends from outside ditch to outside ditch beneath a divided highway will require granular material from the bedding to the haunch of the pipe and suitable material from the ditch to the influence of the pavement section, then granular material over the pipe through the pavement section to the bottom of the subgrade. Suitable material can be used over the pipe across the median and then return to all granular passing through the next set of highway lanes. Finally, the backfill can revert to suitable material over the pipe again beyond the influence of the pavement in the opposite foreslope. Sample Roadway Cross-Section

Each layer or lift is to be compacted to 95% of the maximum unit weight of that material as determined through density testing in accordance with the Density Testing and Inspection Manual. Additional lifts must not be added until a passing density test is achieved. Refer to Appendix K of the Density Testing and Inspection Manual for the minimum frequency of tests required to ensure a sufficient quantity of density testing is being conducted for acceptance.

Compaction equipment should not be run directly on the pipe as it can cause damage to the pipe. At least one lift of cover should be placed over the pipe before running hand-operated compaction equipment over the placed pipe. If the Contractor opts to use a Ho-Pac on a backhoe, at least 3 feet of material should be in place over the pipe before using this equipment. If a Ho-Pac is used, a maximum of 10-inch lifts of backfill can be placed and compacted at one time.

A pneumatic tamp may be required instead of a vibratory compactor for compaction of the haunch areas of a pipe. In these confined working areas, density tests farther out from the culvert cannot be assumed to reflect the compaction under the pipe. Therefore, the efforts of the density Inspector are often the only reliable assurances of adequate compaction in these areas.

Backfilling Around Pipe in Lifts

Jacked-in-Place

Jacked-in-place pipe culverts are used when it is desired to place a drainage feature without disturbing the roadbed or railroad above the pipe. The excavation should not be more than approximately 1 inch greater than the outside diameter of the pipe. The pipe should be advanced with the hole to prevent caving and subsidence of the grade. A steel cutting edge or shield may be attached to the front section of pipe to form and cut the required opening for the pipe. Steel casings are always used for jacked-in-place pipe installed under a railroad.

Frequent checks of the line and grade should be made to ensure the pipe is going in the proper direction.

Steel casing must meet the requirements listed in Table 909-18 of the Standard Specifications for Construction. Adjoining sections should have a tight joint without larger irregularities between the 2 sections. Prior to welding, the steel around the joint should be properly prepared. The steel casing sections must have a fully welded joint which is watertight and capable of withstanding handling and installation stresses. Field welding should be conducted using the shielded metal arc welding process and using E6011 or E7018 electrodes.

Full circular pipe reinforcement is required when concrete pipe is directly jacked-in-place. All joints must have a proper seal. For larger pipes, the joints are to be thoroughly wetted, filled with mortar, and wiped smooth. Voids between the excavation and the pipe are filled using approved grout and grouting methods.

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INSPECTION & TESTING

Inspection

The Inspector should utilize, at a minimum, the following tools to perform the required inspection:

• 100-foot tape measure or longer
• 25-foot tape measure
• Measuring wheel
• Chaining pin
• 6-foot stick ruler
• 4-foot level
• Working plans
• As-built sheets to update the plans
• Survey equipment
• Camera

The Inspector should take the following steps during construction:

1. Verify the correct pipe, gaskets, and geotextile blanket are used per the plans and MSLs.
2. Verify the pipe is free of defects or damage.
   • Using survey paint, mark any rejected pipe with an “R” to indicate rejection of the pipe. It is good practice to mark both the inside and outside of the pipe.
3. Observe installation of pipe, fittings, and appurtenances in accordance with manufacturer’s recommendations.
4. Monitor excavation of the trench to ensure the pipe meets the elevation requirements shown on the plans.
   • If the bell end of the pipe is significantly larger than the spigot, ensure the trench is excavated appropriately so the entire pipe is supported by the bottom of the trench.
5. Verify that all pipe bedding and backfill of excavated trenches is clean, dry, and meets design requirements.
6. Verify there is no debris in the pipe before installation.
7. Verify pipes have lift holes facing the top and the lift holes are filled with concrete plugs and are waterproofed prior to backfilling.
8. When the Contractor is connecting two pipes, ensure:
   • The pipe bell is clean.
   • The required joint gasket is installed.
     • Verify the correct gasket is used as one manufacturer’s specific gasket may not fit a different manufacturer’s pipe.
     • Verify the Contractor lubricates the gasket immediately prior to assembly.
   • The joint is seated properly.
   • A minimum of 12 inches of overlap of the geotextile blanket is obtained on each pipe.
9. Verify the coupler of CMP pipe have been fully bolted prior to backfilling.
10. Obtain grade shots and document the grades on the as-built plans.
11. Verify passing density shots are obtained on each lift of backfill material.
12. Record the density testing results of the backfill material in accordance with the Density Testing and Inspection Manual using the field established maximum density for the material being tested. The minimum testing frequency is shown in Appendix K (backfill) of this manual. The testing frequencies listed are minimums that are satisfactory for acceptance. However, it is emphasized that project conditions normally require more frequent testing for proper density control.
13. Verify permanent outfall labels are located on all outfalls that discharge directly to waters of the state.

Video Inspection

Pipe culvert video inspection must be conducted after installation in accordance with Subsection 402.03.J of the Standard Specifications for Construction. Video inspection is performed by the Contractor. It is required for all types of culverts, with the following exceptions:

• Driveway culverts.
• Culvert extensions of less than 50 feet.
• Extensions of existing catch basin leads of less than 20 feet.
• New culverts of less than 50 feet.

The purpose of the video inspection is to determine any damage or installation defects to the culvert, including pipe deformation, cracking, joint separation, corrosion, perforation, excessive siltation, excessive ponding of water, or any discernable feature observed in the video.

For culverts installed under pavement, the inspection should be conducted after the required backfill compaction of the trench has been achieved, and between 5 and 10 working days prior to pavement surfacing or completion of final grade, except as otherwise approved by the Engineer. For culverts not installed under pavement, the video inspection should be conducted as close to project completion as possible, while still allowing sufficient time for corrective action determined to be necessary from the video inspection and as directed by the Engineer.

All video inspection must be of acceptable quality for the Engineer to review. The camera should provide sufficient lighting and have sufficient underwater capability to provide a clear picture during the inspection. Camera magnification must always be indicated on the screen during video inspection. The camera must allow tilting and panning for the inspection of joints, cracks, and other defects. If the Engineer determines the video quality to be unsatisfactory, re-inspection of the pipes may be required at no cost to the contract. Re-inspection may also be required if the joints or defects are not fully inspected during the initial video inspection, at no cost to the contract.

If defects are found during video inspection, the Contractor is to submit a corrective action plan to the Engineer for review and approval. Only after the plan is approved, may the Contractor begin corrective action work.

Testing

For evaluation of aggregate materials, use only certified aggregate sampling and testing technicians. Refer to the Procedures for Aggregate Inspection manual and project specifications for testing requirements and frequencies. The Engineer should track the approved testing of installed aggregate and coordinate with the respective testing lab to ensure the required number of aggregate tests for the project are being completed.

Perform density testing on compacted backfill. All backfill, regardless of material used, is to be compacted to 95% of the maximum unit weight. Density tests need to be taken as close to the pipe as possible to maintain accurate information. The Inspector should ensure the minimum number of required density tests are being performed per the Density Testing and Inspection Manual.

To ensure excessive deformation of the pipe will not occur after backfilling and compaction, mandrel testing must be performed on a sample of all plastic pipes. Refer to Division 4 Supplemental Information of the Construction Manual for more information on mandrel testing of plastic pipe.

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MEASUREMENT, DOCUMENTATION & PAYMENT

Measurement and Payment

In situ material from the job site may be used for backfilling after the Contractor completes gradation testing of samples taken from an onsite stockpile. The respective MDOT material lab will confirm the gradation of the onsite material meets the requirements for the desired backfill material.

Refer to Subsection 401.04 of the Standard Specifications for Construction for direction regarding measurement and payment for culverts.

In general, culverts are paid by the linear foot for the size of the culvert being installed. Excavation, dewatering, joint wrapping, and backfill are incidental to the culvert pay item. The cost to restrain the pipe during backfilling and provide temporary cover to protect the pipe from damage will be included with the appropriate item of work and not paid for separately. End sections and existing culvert removals are paid for separately.

End sections are paid by the culvert pipe size as “each” and include the hardware to connect them to the culvert.

Cast-in-place headwalls are paid for as Concrete Grade 3500 in cubic yards and reinforcement steel weight in pounds in accordance with Subsection 706.04 of the Standard Specifications for Construction. If the Contractor elects to use precast headwalls, measurement and payment is by “each.”

End sections and headwalls that outlet to waters of the state require an outfall label. The outfall is paid as “each.” Notes about the size and location for the outfall label are included in the Standard Plan R-85 series.

Documentation

The primary report required for the payment of culverts is the Daily Work Report (DWR). The Inspector should note in the remarks section of the report the condition of the base material during placement, material verification, and equipment and manpower used. The invert elevations at both the inlet and the outlet ends as well as the final length of the culvert should be recorded for as-built records.

Additional documentation once the work is completed should include:

1. Station to station length and width being paid on this date.
2. Survey or other approved methods for verification the culvert was constructed in conformance with the project documents.
3. Volume and tonnage of bedding and backfill material placed.
4. Video records of pipe inspections.

Form 1900, Aggregate Inspection Daily Report, will need to be completed for every sublot of aggregate to track gradation acceptance.

Form 0582B, Moisture & Density Determination - Nuclear Method, is used to record density testing results.

Delivery tickets must be verified for the source of material against the approved Material Source List. Each ticket must include the required information. Refer to Subsection 109.01.B.6 of the Standard Specifications for Construction for the information required on each ticket.

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LOCAL AGENCY PROJECTS

Local agency projects sometimes have details and specifications for pipe culvert construction. These standards are to be followed while working on a Local Agency Project.

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RAIL PROJECTS

-Reserved-

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