401 - 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:
- Inlet: Inlets are typically end sections or headwalls to permit water to enter into the system.
- Pipe: Pipe is the conduit responsible for transporting water to the outlet. Project documents specify the size and material of the pipes.
- Outlet: Outlets are typically end sections or headwalls which discharges water to a ditch, a body of water, or a basin.
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.
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.
To aid in the joining of pipe segments and to seal the pipe so the joints do not leak, lubricant and gaskets are used.
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.
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.
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.
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.
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
PRECONSTRUCTION
Prior to the start of construction, the Inspector should perform the following:
- 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.
- Verify the pipe meets the requirements contained in the plans, specifications, and any addenda.
- 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.
- Verify existing underground utility markings.
- Take note of any potential utility crossings and reference the plans and profiles to ensure minimum clearances are met.
- 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.
- 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.