Difference between revisions of "404 - Underdrain"

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404 - Underdrain
 
  
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* [[404.01 - General]]
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<center><span STYLE="font: 60pt arial;">'''404'''</span></center>
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* [[404.02 - Materials]]
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* [[404.03 - Measurement]]
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<center><span STYLE="font: 40pt arial;">'''Underdrains'''</span></center>
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==[[#GENERAL|GENERAL DESCRIPTION]]==
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 +
=== Definitions of Terms ===
 +
'''Aggregate''': Aggregate refers to the material used as the foundation of infrastructure. It typically consists of sand, gravel, crushed stone, or recycled materials like concrete.
 +
 
 +
'''Approach''': An approach is the section of roadway leading up to a bridge, culvert, or a main roadway. It is designed to provide a smooth transition.
 +
 
 +
'''Dense-Graded Aggregate''': Dense-graded aggregate is a mixture of aggregates with an even distribution of different size aggregates.
 +
Fine-Graded Aggregate: Fine-graded aggregate is a mixture of aggregates with a uniform distribution of small size aggregate particles passing through a #4 sieve.
 +
 
 +
'''Open-Graded Aggregate''': Open-graded aggregate is a type of aggregate material characterized by a high porosity and void content, allowing water to drain through freely. It is commonly used in drainage applications to prevent water accumulation on road surfaces.
 +
 
 +
'''Salvaged Aggregate''': Salvaged aggregate refers to granular material salvaged from the project site. The material is tested to meet specific gradation requirements prior to re-use on the project.
 +
Shoulder: The shoulder is the portion of the roadway adjacent to the main driving lanes. It provides additional space for emergency stopping, vehicle breakdowns, and non-motorized use, and also helps to support the road edge.
 +
 
 +
'''Stone''': Stone refers to a naturally occurring mineral material, typically used as aggregate in concrete, asphalt, riprap, and road base layers. Stones vary in size and composition, with common types including granite, limestone, and basalt.
 +
 
 +
'''Subbase''': Subbase is a layer of material placed beneath the road surface or pavement layers and roadway base course. It provides additional support, drainage, and stability to the pavement structure, helping to distribute loads and prevent uneven settlement.
 +
 
 +
'''Subgrade''': Subgrade is the existing ground or soil surface upon which the road or pavement section is constructed. It serves as the foundation for the road layers above and must be properly prepared and compacted to ensure stability and durability.
 +
 
 +
=== General Overview ===
 +
Underdrains play a crucial role in providing drainage, particularly in ensuring the stability and longevity of the roadway. These drainage systems are designed to manage groundwater by preventing its accumulation beneath the road surface. By effectively channeling water away from the pavement layers, underdrains help to mitigate the risk of soil saturation, erosion, and the subsequent weakening of the roadbed. This is especially important in areas with high water tables or frequent precipitation. Underdrains typically consist of perforated pipes installed in the road's subbase or subgrade layers, allowing water to flow freely away from the pavement structure. Properly installed underdrains enhance the overall durability and long term performance of the road, reducing the likelihood of costly repairs and ensuring safer driving conditions for motorists.
 +
{{top}}
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 +
==[[#MATERIALS|MATERIALS]]==
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All materials must meet acceptance requirements in the [https://www.michigan.gov/mdot/Business/Construction/Materials-Source-Guide Materials Source Guide] and be listed on the Contractor-provided Material Source Lists in the project files.
 +
 
 +
=== Description of Materials ===
 +
Refer to the [https://mdotjboss.state.mi.us/stdplan/getStandardPlanDocument.htm?docGuid=b22a66f3-4853-4730-8aaa-cca6ab2c6fa9 Standard Plan R-80 series] for specific underdrain type material use.
 +
 
 +
==== Granular Material Class IIAA ====
 +
Granular backfill, often comprised of sand, is used to fill the trench around the underdrain system components. This material provides support and stability to the drainage system while facilitating water movement. Generally, granular material Class IIAA is used with sock wrapped underdrain pipe.
 +
 
 +
==== Open-Graded Aggregate (Class 34R) ====
 +
Open-graded aggregate Class 34R is a material that has a uniform gradation which allows for relatively high permeability and is used to backfill perforated underdrain pipe. This provides a stable medium for water to flow through while preventing soil intrusion into the drainage system.
 +
 
 +
==== Outlet Endings and Outlets ====
 +
Underdrain outlet endings and outlet pipe sections direct water away from the underdrain system. Either a corrugated metal or solid PVC (polyvinyl chloride) pipe is used for underdrain outlets to facilitate the discharge of water into designated drainage areas. A concrete or metal outlet ending is installed on the end of the outlet pipe to complete the transition to the designated drainage area. In areas with enclosed drainage, such as storm sewer systems, the underdrain pipe will outlet directly into catch basins which may have inlet holes already installed. Concrete outlet endings are required for PVC outlets.
 +
 
 +
==== Perforated Pipe ====
 +
Underdrain pipe is perforated pipe and is typically made of corrugated HDPE (high-density polyethylene), polypropylene, or PVC. It features evenly spaced holes along the length, allowing water to enter and flow through the pipe. Depending on the underdrain type, the pipe may come with a geosynthetic sock wrapped over the pipe.
 +
 
 +
==== Drainage Marker Posts ====
 +
Drainage marker posts are used to indicate the presence and location of drainage infrastructure, such as underdrain outlet endings or culverts.
 +
 
 +
==== Geosynthetics ====
 +
Geosynthetics are synthetic fabrics made from materials like polypropylene or polyester, primarily used for separating materials, such as a sand subbase and an aggregate base. In some cases, geosynthetic fabrics are used to facilitate the drainage of storm water that infiltrates the road base by directing the water to an underdrain system or to ditches. These materials are important because they enhance the structural integrity of infrastructure, reduce the need for additional material layers, improve drainage, and extend the lifespan of roadways by reducing soil movement and providing necessary reinforcement.
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=== Pictures of Materials ===
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{|
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|+
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|-
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| [[File:208-009.jpg|300px|thumb|center|'''''34RAggregate''''']]|| [[File:Class II Granular Material.jpg|300px|thumb|center|'''''Class II Sand''''']]
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|-
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| [[File:404 (3).jpg|300px|thumb|center|'''''Underdrain Outlet End Section with Grate''''']] || [[File:404 (4).jpg|300px|thumb|center|'''''Underdrain Pipe Both Wrapped and Unwrapped''''']]
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|}
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==[[#EQUIPMENT|EQUIPMENT]]==
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The following equipment is typically used for construction of underdrain:
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* Paddle wheel tractor scraper
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* Mini excavator
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* Skid steer
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* Bulldozer
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* Front end loader
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* Pipe trencher
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* Dump truck
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 +
=== Description of Equipment ===
 +
Depending on the underdrain installation scope, the Contractor can install underdrain in a variety of ways.
 +
 
 +
* Large Projects with Long Underdrain Runs: A pipe trencher or paddle wheel tractor scraper can be used for trenching. In either case, the machine digs the trench for the pipe and places the underdrain pipe simultaneously. In cases where the trench must be lined with a geotextile fabric before pipe installation, these machines are only used to trench for the pipe installation. A front end loader backfills the pipe with the assistance of a laborer. The laborer ensures the right amount of aggregate is added to the trench and the pipe does not float up as the aggregate is being dropped on it.
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* Small Projects with Short Underdrain Runs: A mini excavator is used to dig the trench for the underdrain pipe. The pipe and any required geotextile fabric is placed in the trench by hand. A front end loader backfills the pipe with the assistance of a laborer. The laborer ensures the right amount of aggregate is added to the trench and the pipe does not float up as the aggregate is being dropped on it.
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 +
In cases where the underdrain is being installed in an open trench within the subgrade or subbase and the trench is not lined, a bulldozer can be used to backfill the trench. Either a front end loader or dump truck drops aggregate material to backfill the pipe along lined trench.
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 +
=== Pictures of Equipment ===
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 +
{|
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|+
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|-
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| [[File:404 (5).jpg|300px|thumb|center|'''''Dump Truck, Bulldozer, and Skid Steer Installing Subbase Underdrain and Subbase''''']] || [[File:Pipe trencher.jpg|300px|thumb|center|'''''Pipe Trencher Installing Underdrain''''']]
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|}
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{{top}}
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==[[#PRECONSTRUCTION|PRECONSTRUCTION]]==
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 +
Prior to the start of construction, the Inspector should perform the following:
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 +
# Review the plans to verify the location of the work.
 +
* Centerline road profiles can be referenced to determine low points for outlet placement.
 +
* Typical cross-sections should be reviewed for underdrain alignment relative to the proposed roadway. Typically, underdrain is placed outside the limits of traffic, or if required, in the center of lanes away from the wheel paths of traffic.
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# Verify the type of underdrain that will be installed. Refer to the [https://mdotjboss.state.mi.us/stdplan/getStandardPlanDocument.htm?docGuid=b22a66f3-4853-4730-8aaa-cca6ab2c6fa9 Standard Plan R-80 series] for specific details on installation requirements.
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# Verify there is an approved Contractor-submitted Underdrain Outlet Plan in the project files.
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# Verify the existing subgrade is in sound condition and has been accepted. A proof roll or geotechnical analysis may be conducted to determine condition of existing subgrade. If poor soils are encountered, coordinate with the Engineer and Region Soils Engineer for testing and/or removal of the soils.
 +
# Verify a surveyor has provided stakes for the work.
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# Review survey stakes and underdrain outlet locations to verify the underdrain can drain into a ditch or a drainage structure in the storm sewer system.
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# Verify the subgrade is at the elevation and cross-slope specified in the project specifications.
 +
# Review the plans and the Special Provision for Maintenance of # Traffic. There may be restrictions or staging requirements for the installation of the underdrain. Installation restrictions are typically associated with staging requirements on a project and access to side streets and driveways.
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# Verify all materials are approved for use and meet specifications, and verify that stockpiled materials are protected from weather and sunlight as required by the specifications and manufacturer recommendations.
 +
# Obtain photographs of material tickets, storage method, and location.
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# Obtain samples of the geotextile blanket and underdrain pipe in accordance with the [https://www.michigan.gov/mdot/Business/Construction/Materials-Source-Guide Materials Source Guide] for testing and acceptance.
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# Visually inspect the underdrain and geotextile blanket for tears, breaks, or crushed pipe.
 +
# Hold an onsite meeting with the Contractor to discuss:
 +
#* The construction methods that will be used to complete the work.
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#* Underdrain outlets being installed through the haul route and how they will be protected during construction.
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#* Marking of underdrain outlets on the pavement shoulders.
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#* Notification by the Contractor to video record the underdrain outlet prior to paving.
 +
#** [https://mdotjboss.state.mi.us/SpecProv/getSSSPDocumentById.htm?projNum=704577&fileName=20SP-404A-01.pdf Special Provision for Video Inspection of Underdrain (20SP-404A-01)] is typically included in all projects with underdrain outlets.
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#* Required traffic control measures, proximity of traffic to the work area, and maintaining driveways during construction.
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#* How they intend to prevent contamination of existing material during trenching operations.
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#* Communication required if impacting residents or businesses during installation.
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#** 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.
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#* Review local ordinances.
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#* Disposal of excavated material and material stockpile locations. The Contractor should provide authorization letters to the Engineer noting material stockpile and disposal locations.
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#* Soil erosion and sedimentation control measures that will be utilized to minimize soil erosion and subsequent sedimentation.
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#* Methods for securing the site during work operations and at the end of each workday.
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 +
In some instances, the plans may detail the intended outlet locations, a review of the plans is warranted.
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[[File:404 (7).jpg|300px|thumb|center|'''''Sample Plan Sheet indicating Outlet Locations''''']]
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{{top}}
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 +
==[[#CONSTRUCTION|CONSTRUCTION]]==
 +
The plans show the underdrain alignment within the typical roadway section. Trench width and depth can vary based on the size of the pipe used. Refer to the plans and [https://mdotjboss.state.mi.us/stdplan/getStandardPlanDocument.htm?docGuid=b22a66f3-4853-4730-8aaa-cca6ab2c6fa9 Standard Plan R-80] series for trench width details. All underdrain must be installed with a continuous grade to ensure there are no high or low points. No contamination of other roadway layers should occur during underdrain installation.
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 +
=== Bank Underdrain ===
 +
When slopes have significant runoff or seepage, underdrain will be installed in the bank to collect water and prevent slope erosion. Typically, the first bank underdrain run is installed at the top of the bank, with additional runs spaced out throughout the bank. The amount and spacing of subsequent runs depends on total water runoff and seepage. Installation begins with excavation of the trench in accordance with the plan locations. The bottom of the trench should be formed to the shape of the pipe. Pipe installation typically includes a wrapped underdrain pipe being placed at the bottom of the trench before being backfilled with granular material Class II AA and compacted. Caution needs to be used during compaction of the backfill to ensure the pipe is not damaged while compacting the backfill material.
 +
 
 +
An open-graded version of bank underdrain can be installed. This includes:
 +
# Lining the trench with a geotextile blanket.
 +
# Placing 1 to 2 inches of backfill below the underdrain pipe.
 +
# Placing a nonwrapped underdrain pipe.
 +
# Backfilling with open-graded aggregate Class 34R.
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 +
=== Subgrade Underdrain ===
 +
Subgrade underdrain is installed beneath the shoulder of the roadway to a depth of 5 feet below the surface of the shoulder and 4 feet from the edge of the travel lane. The bottom of the trench should be formed to the shape of the pipe. A wrapped underdrain pipe is placed in the bottom of the trench before being backfilled with granular material Class II AA and compacted. Caution needs to be used during compaction of the backfill to ensure the pipe is not damaged while compacting the backfill material.
 +
 
 +
An open-graded version of subgrade underdrain can be installed. This includes:
 +
# Lining the trench with a geotextile blanket. 
 +
# Placing 1 to 2 inches of backfill below the underdrain pipe.
 +
# Placing a nonwrapped underdrain pipe. 
 +
# Backfilling with open-graded aggregate Class 34R.
 +
 
 +
=== Subbase Underdrain ===
 +
Subbase underdrain is installed a maximum of 10 inches below the top of the subgrade either under the roadway or shoulder. If installed under the roadway, the placement is typically designed to not be under a wheel path of traffic. Once the trench is excavated and the bottom of the trench formed to the shape of the pipe, wrapped underdrain pipe is placed in the trench. Granular material Class II AA is placed as backfill around the pipe and to the top of the trench. A minimum of 2 inches of cover from the top of the underdrain pipe to the bottom of the subbase must be obtained. Caution needs to be used during compaction of the backfill to ensure the pipe is not damaged while compacting the backfill material.
 +
 +
[[File:404 (8).jpg|300px|thumb|center|'''''Subbase Underdrain Pipe Installed in Trench''''']]
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 +
=== Open-Graded Underdrain ===
 +
Open-graded underdrain is installed within the subgrade with the top of the trench at the same elevation as the top of the subbase in the roadway or shoulder. Be sure not to get this confused with the other types of underdrain, which have open-graded variants. There are 2 main types of open-graded underdrain: with geotextile separator or with dense-graded aggregate as a separation layer. Refer to the S[https://mdotjboss.state.mi.us/stdplan/getStandardPlanDocument.htm?docGuid=b22a66f3-4853-4730-8aaa-cca6ab2c6fa9 tandard Plan R-80 series] for more details on open-graded underdrain installation.
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 +
# '''With a geotextile separator''' refers to a geotextile separator being placed between the subbase and OGDC layers of a roadway. Before placing the geotextile separator on top of the subbase, the open-graded underdrain is installed. The trench is excavated through the subbase and into the subgrade forming the bottom of the trench to the shape of the pipe. A geotextile blanket is placed to line the trench before the nonwrapped underdrain pipe is placed. The geotextile blanket should overlap the top of the trench a minimum of 1 foot. Ensure 1 to 2 inches of 34R backfill material is placed under the pipe before the remainder of the trench is filled. There will be 2 to 3 inches of 34R backfill material placed over the top of the trench to 6 inches beyond the edge of the trench.
 +
# '''With a dense-graded aggregate''' refers to a dense-graded aggregate layer being placed between the subbase and open-graded aggregate base layers of the roadway. Before the open-graded aggregate base layer is installed, the open-graded underdrain must be installed. The trench is excavated through the dense-graded aggregate base, the subbase, and into the subgrade forming the bottom of the trench to the shape of the pipe. A geotextile blanket is placed to line the trench before the nonwrapped underdrain pipe is placed. The geotextile blanket should overlap the top of the trench a minimum of 1 foot. Ensure 1 to 2 inches of open-graded aggregate Class 34R backfill material is placed under the pipe before the remainder of the trench is filled. There will be 2 to 3 inches of 34R backfill material placed over the top of the trench to 6 inches beyond the edge of the trench.
 +
 +
{|
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|+
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|-
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| [[File:404 (9).jpg|300px|thumb|center'''''Open-Graded Pipe in the Lined Trench''''']] || [[File:404 (10).jpg|300px|thumb|center|'''''34R Backfill Place in the Open-Graded Underdrain Tench''''']]
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|}
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=== Outletting Underdrain ===
 +
Outlet locations should be in accordance with the plans or the [https://mdotjboss.state.mi.us/stdplan/getStandardPlanDocument.htm?docGuid=b22a66f3-4853-4730-8aaa-cca6ab2c6fa9 Standard Plan R-80 series], at all low points and should not exceed 300-foot spacing between outlets. At outlet locations, a 5-foot section of the perforated pipe is bent to form an arc in accordance with [https://mdotjboss.state.mi.us/stdplan/getStandardPlanDocument.htm?docGuid=b22a66f3-4853-4730-8aaa-cca6ab2c6fa9 Standard Plan R-80 series] prior to transitioning to the solid outlet pipe. The use of wyes or tees is prohibited. Connections between underdrain and outlet pipes should be in accordance with the manufacturer’s recommendations or by Engineer approval. If the outlet is tapped into a drainage structure, the cored or sawed hole in the structure should be sealed with brick and mortar. When draining to a roadside ditch, outlets should be run at minimum of 4% grade and maintain 4 inches of freeboard above the ditch invert. The outlet pipe installed should be either corrugated metal pipe or PVC with the corresponding concrete or metal outlet endings. The percent grade can be adjusted to meet outlet elevation requirements. Outlet ending locations should be marked on the shoulder of the road with a stencil as well as a drainage marker post. Metal end sections are not permitted on PVC outlet pipe.
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{|
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|+
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|-
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| [[File:404 (11).jpg|300px|thumb|center'''''PVC Outlet for Subbase Underdrain''''']] || [[File:404 (12).jpg|300px|thumb|center|'''''Underdrain Outlet Tapped into a Drainage Structure''''']]
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|}
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{{top}}
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==[[#INSPECTION & TESTING|INSPECTION & TESTING]]==
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=== Inspection ===
 +
The Inspector should utilize, at a minimum, the following tools to perform the required inspection:
 +
* Measuring wheel
 +
* 100-foot tape measure or longer
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* 25-foot tape measure
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* Chaining pin
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* 6-foot stick ruler
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* 4-foot level
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* Working plans
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* String line or laser level if traditional survey stakes are used
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* Camera
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* Survey equipment
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 +
The Inspector should take the following steps during construction:
 +
# Check the trench dimensions to ensure the Contractor is meeting the specification requirements.
 +
# Monitor the trenching operation to ensure cross-contamination of other materials does not occur.
 +
# Inspect the underdrain pipes for proper alignment, grade, and placement within the trench. Ensure the pipes are securely connected and any required fittings or joints are properly installed.
 +
# Examine the backfill material surrounding the underdrain pipes to ensure it meets the specified gradation and compaction requirements. Verify the backfill is uniformly compacted in layers to provide adequate support and stability to the underdrain system.
 +
# Obtain material tickets.
 +
# If geotextile blanket is specified in the design, inspect the installation to ensure it is properly installed prior to placement of the backfill material. Verify the fabric is securely fastened and overlaps correctly to serve as an effective filter.
 +
# Verify the installation of end caps on the upstream end or outlets and outlet ends at the ends of the underdrain system. Cutting the underdrain pipe and folding the end or tying the end of the sock are not approved methods for capping the end of the underdrain. Ensure end sections provide a smooth transition for water flow and outlets are positioned to discharge water away from the roadway.
 +
 
 +
==== Video Inspection ====
 +
All underdrain must be video inspected in accordance with the Special Provision for Video Inspection of Underdrain (20SP-404A-01). The Inspector is required to witness the Contractor record the video of the underdrain as a copy of the video is not provided. The arc of the underdrain for outletting purposes should not be greater than 90 degrees to allow the camera to be pushed past the outlet into the mainline run of underdrain. The purpose of the video inspection is to identify any installation defects in the underdrain pipe/underdrain outlet pipe such as:
 +
 
 +
* Crushed pipe.
 +
* Separated joints.
 +
* Plugged underdrain and/or underdrain outlet pipe.
 +
* Standing water exceeding half the pipe diameter for a distance of 25 feet or more.
 +
* Other anomalies.
 +
 
 +
The video inspection of open-graded underdrain should be performed after the mainline pavement is placed but before the shoulder is paved. Underdrain should be video inspected, including open-graded underdrain, prior to pavement placement if located under pavement but after placement of the aggregate base. The underdrain outlets, including outlet endings, must be completely installed prior to conducting the video inspection. Defects found must be excavated and repaired, and/or removed and replaced, via a method proposed by the Contractor and meeting the Engineer’s prior approval.
 +
 
 +
==== Underdrain Inspection ====
 +
Common problems with underdrain installation have been observed in the past. The Inspector should take the following steps when inspecting underdrain:
 +
 
 +
* For open-graded underdrain, ensure the geotextile separator is not placed over an open-graded underdrain trench (on projects where geotextile separator is called for between the sand subbase and open-graded drainage course). This does not allow the system to function correctly.
 +
* Verify there are no improper connections made within the outlet pipe. If connections are required in the outlet pipe, they must be watertight, and the connectors must be of the same material as the outlet pipe (e.g., rigid PVC outlet pipe needs connections made with rigid PVC connectors).
 +
* Confirm the use of properly sized concrete rings (when Concrete Ring Option for outlet endings is used). The [https://mdotjboss.state.mi.us/stdplan/getStandardPlanDocument.htm?docGuid=b22a66f3-4853-4730-8aaa-cca6ab2c6fa9 Standard Plan R-80 series] calls for 3-foot lengths for the concrete rings and 2-foot lengths have been incorrectly installed in the past. If concrete end sections are used, they are typically 2 feet in length.
 +
* Verify there are no sags in the underdrain pipe just before it connects to the underdrain outlet pipe.
 +
 
 +
=== Testing ===
 +
For evaluation of aggregate materials, use only certified aggregate sampling and testing technicians. Refer to the [https://www.michigan.gov/mdot/-/media/Project/Websites/MDOT/Business/Construction/Standard-Specifications-Construction/CFS-Manuals/Procedures-Aggregate-Inspection.pdf?rev=e2f19aadca344460afca48b7b9ddb31e&hash=5D3CB25E2CD084FACCFD616004CCEB82 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.
 +
 
 +
For every new source, new day, or suspected change in material, a moisture check needs to be completed. Obtaining moisture readings from a nuclear density gauge is an acceptable method to gauge moisture results of material in the field. Final determination of moisture content will be made from a field sample stored in a plastic bag with the moisture content checked for payment using the oven dry method only if it’s paid for by weight.
 +
 
 +
Density for each lift needs to be achieved before subsequent layers are built up. The maximum lift thickness permitted is 12 inches after compaction. For foundation, bank, subbase, and subgrade underdrains and outlets within the influence of the roadbed, density needs to achieve a minimum of 95% compaction. The Inspector should ensure the minimum number of required density tests are being performed per the [https://www.michigan.gov/mdot/-/media/Project/Websites/MDOT/Business/Construction/Standard-Specifications-Construction/CFS-Manuals/Density-Testing-Inspection-Manual.pdf?rev=6ea61069b3b649e5bbd9362f000a4e0b&hash=44138356CA520616DF23E2E1D8E49AE0 Density Testing and Inspection Manual].
 +
 
 +
Geosynthetic materials must be tested according to the [https://www.michigan.gov/mdot/-/media/Project/Websites/MDOT/Business/Construction/Materials-Quality-Assurance-Procedures/2023-MQAP-Final-Links.pdf?rev=67f395ebd7dd49eeaf8061226ef47efd&hash=A1CA9FFDE08C78A232A52DACA633D1BE Materials Quality Assurance Procedures (MQAP) Manual] prior to installation on the project. The Inspector should work with the testing agency to obtain a sample prior to installation of the material. Geotextiles must be unwrapped one full roll circumference prior to sampling. All samples must be rolled, not folded, during shipment to prevent creases in the fabric.
 +
{{top}}
 +
 
 +
==[[#MEASUREMENT, DOCUMENTATION & PAYMENT|MEASUREMENT, DOCUMENTATION & PAYMENT]]==
 +
=== Measurement and Payment ===
 +
Underdrains are measured in place by length in feet along the centerline of the underdrain. Inspector should note starting and stopping stations and the station of the outlets.
 +
 
 +
=== Documentation ===
 +
The primary report required for the payment of underdrains 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.
 +
Sketches and calculations documenting the work is completed is required and should include:
 +
# Station to station length and trench width being paid on this date.
 +
# Survey or other approved methods for verification the underdrain was constructed in conformance with the project documents.
 +
#* Collecting the GPS location of all underdrain outlets for as-built plans is good practice.
 +
# Volume and tonnage of material placed.
 +
[https://mdotjboss.state.mi.us/webforms/GetDocument.htm?fileName=1900.pdf Form 1900, Aggregate Inspection Daily Report], will need to be completed for every sublot of aggregate to track gradation acceptance.
 +
 
 +
[https://mdotjboss.state.mi.us/webforms/GetDocument.htm?fileName=0582B.pdf 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 Materials Source List. Each ticket must include the required information. Refer to Subsection 109.01.B.6 of the [https://mdotwiki.state.mi.us/images_construction/9/95/2020-Standard-Specifications-Construction.pdf#page=110 Standard Specifications for Construction] for the information required on each ticket.
 +
 
 +
{{top}}
 +
 
 +
==[[#LOCAL AGENCY PROJECTS|LOCAL AGENCY PROJECTS]]==
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[[Category:Construction Manual]]
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[[Category:Division 4]]
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[[Category:Section 404]]
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[[Category:New CM Format]]

Latest revision as of 11:14, 8 October 2025

404
Underdrains


GENERAL DESCRIPTION

Definitions of Terms

Aggregate: Aggregate refers to the material used as the foundation of infrastructure. It typically consists of sand, gravel, crushed stone, or recycled materials like concrete.

Approach: An approach is the section of roadway leading up to a bridge, culvert, or a main roadway. It is designed to provide a smooth transition.

Dense-Graded Aggregate: Dense-graded aggregate is a mixture of aggregates with an even distribution of different size aggregates. Fine-Graded Aggregate: Fine-graded aggregate is a mixture of aggregates with a uniform distribution of small size aggregate particles passing through a #4 sieve.

Open-Graded Aggregate: Open-graded aggregate is a type of aggregate material characterized by a high porosity and void content, allowing water to drain through freely. It is commonly used in drainage applications to prevent water accumulation on road surfaces.

Salvaged Aggregate: Salvaged aggregate refers to granular material salvaged from the project site. The material is tested to meet specific gradation requirements prior to re-use on the project. Shoulder: The shoulder is the portion of the roadway adjacent to the main driving lanes. It provides additional space for emergency stopping, vehicle breakdowns, and non-motorized use, and also helps to support the road edge.

Stone: Stone refers to a naturally occurring mineral material, typically used as aggregate in concrete, asphalt, riprap, and road base layers. Stones vary in size and composition, with common types including granite, limestone, and basalt.

Subbase: Subbase is a layer of material placed beneath the road surface or pavement layers and roadway base course. It provides additional support, drainage, and stability to the pavement structure, helping to distribute loads and prevent uneven settlement.

Subgrade: Subgrade is the existing ground or soil surface upon which the road or pavement section is constructed. It serves as the foundation for the road layers above and must be properly prepared and compacted to ensure stability and durability.

General Overview

Underdrains play a crucial role in providing drainage, particularly in ensuring the stability and longevity of the roadway. These drainage systems are designed to manage groundwater by preventing its accumulation beneath the road surface. By effectively channeling water away from the pavement layers, underdrains help to mitigate the risk of soil saturation, erosion, and the subsequent weakening of the roadbed. This is especially important in areas with high water tables or frequent precipitation. Underdrains typically consist of perforated pipes installed in the road's subbase or subgrade layers, allowing water to flow freely away from the pavement structure. Properly installed underdrains enhance the overall durability and long term performance of the road, reducing the likelihood of costly repairs and ensuring safer driving conditions for motorists.

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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

Refer to the Standard Plan R-80 series for specific underdrain type material use.

Granular Material Class IIAA

Granular backfill, often comprised of sand, is used to fill the trench around the underdrain system components. This material provides support and stability to the drainage system while facilitating water movement. Generally, granular material Class IIAA is used with sock wrapped underdrain pipe.

Open-Graded Aggregate (Class 34R)

Open-graded aggregate Class 34R is a material that has a uniform gradation which allows for relatively high permeability and is used to backfill perforated underdrain pipe. This provides a stable medium for water to flow through while preventing soil intrusion into the drainage system.

Outlet Endings and Outlets

Underdrain outlet endings and outlet pipe sections direct water away from the underdrain system. Either a corrugated metal or solid PVC (polyvinyl chloride) pipe is used for underdrain outlets to facilitate the discharge of water into designated drainage areas. A concrete or metal outlet ending is installed on the end of the outlet pipe to complete the transition to the designated drainage area. In areas with enclosed drainage, such as storm sewer systems, the underdrain pipe will outlet directly into catch basins which may have inlet holes already installed. Concrete outlet endings are required for PVC outlets.

Perforated Pipe

Underdrain pipe is perforated pipe and is typically made of corrugated HDPE (high-density polyethylene), polypropylene, or PVC. It features evenly spaced holes along the length, allowing water to enter and flow through the pipe. Depending on the underdrain type, the pipe may come with a geosynthetic sock wrapped over the pipe.

Drainage Marker Posts

Drainage marker posts are used to indicate the presence and location of drainage infrastructure, such as underdrain outlet endings or culverts.

Geosynthetics

Geosynthetics are synthetic fabrics made from materials like polypropylene or polyester, primarily used for separating materials, such as a sand subbase and an aggregate base. In some cases, geosynthetic fabrics are used to facilitate the drainage of storm water that infiltrates the road base by directing the water to an underdrain system or to ditches. These materials are important because they enhance the structural integrity of infrastructure, reduce the need for additional material layers, improve drainage, and extend the lifespan of roadways by reducing soil movement and providing necessary reinforcement.

Pictures of Materials

34RAggregate
Class II Sand
Underdrain Outlet End Section with Grate
Underdrain Pipe Both Wrapped and Unwrapped

EQUIPMENT

The following equipment is typically used for construction of underdrain:

  • Paddle wheel tractor scraper
  • Mini excavator
  • Skid steer
  • Bulldozer
  • Front end loader
  • Pipe trencher
  • Dump truck

Description of Equipment

Depending on the underdrain installation scope, the Contractor can install underdrain in a variety of ways.

  • Large Projects with Long Underdrain Runs: A pipe trencher or paddle wheel tractor scraper can be used for trenching. In either case, the machine digs the trench for the pipe and places the underdrain pipe simultaneously. In cases where the trench must be lined with a geotextile fabric before pipe installation, these machines are only used to trench for the pipe installation. A front end loader backfills the pipe with the assistance of a laborer. The laborer ensures the right amount of aggregate is added to the trench and the pipe does not float up as the aggregate is being dropped on it.
  • Small Projects with Short Underdrain Runs: A mini excavator is used to dig the trench for the underdrain pipe. The pipe and any required geotextile fabric is placed in the trench by hand. A front end loader backfills the pipe with the assistance of a laborer. The laborer ensures the right amount of aggregate is added to the trench and the pipe does not float up as the aggregate is being dropped on it.

In cases where the underdrain is being installed in an open trench within the subgrade or subbase and the trench is not lined, a bulldozer can be used to backfill the trench. Either a front end loader or dump truck drops aggregate material to backfill the pipe along lined trench.

Pictures of Equipment

Dump Truck, Bulldozer, and Skid Steer Installing Subbase Underdrain and Subbase
Pipe Trencher Installing Underdrain


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PRECONSTRUCTION

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

  1. Review the plans to verify the location of the work.
  • Centerline road profiles can be referenced to determine low points for outlet placement.
  • Typical cross-sections should be reviewed for underdrain alignment relative to the proposed roadway. Typically, underdrain is placed outside the limits of traffic, or if required, in the center of lanes away from the wheel paths of traffic.
  1. Verify the type of underdrain that will be installed. Refer to the Standard Plan R-80 series for specific details on installation requirements.
  2. Verify there is an approved Contractor-submitted Underdrain Outlet Plan in the project files.
  3. Verify the existing subgrade is in sound condition and has been accepted. A proof roll or geotechnical analysis may be conducted to determine condition of existing subgrade. If poor soils are encountered, coordinate with the Engineer and Region Soils Engineer for testing and/or removal of the soils.
  4. Verify a surveyor has provided stakes for the work.
  5. Review survey stakes and underdrain outlet locations to verify the underdrain can drain into a ditch or a drainage structure in the storm sewer system.
  6. Verify the subgrade is at the elevation and cross-slope specified in the project specifications.
  7. Review the plans and the Special Provision for Maintenance of # Traffic. There may be restrictions or staging requirements for the installation of the underdrain. Installation restrictions are typically associated with staging requirements on a project and access to side streets and driveways.
  8. Verify all materials are approved for use and meet specifications, and verify that stockpiled materials are protected from weather and sunlight as required by the specifications and manufacturer recommendations.
  9. Obtain photographs of material tickets, storage method, and location.
  10. Obtain samples of the geotextile blanket and underdrain pipe in accordance with the Materials Source Guide for testing and acceptance.
  11. Visually inspect the underdrain and geotextile blanket for tears, breaks, or crushed pipe.
  12. Hold an onsite meeting with the Contractor to discuss:
    • The construction methods that will be used to complete the work.
    • Underdrain outlets being installed through the haul route and how they will be protected during construction.
    • Marking of underdrain outlets on the pavement shoulders.
    • Notification by the Contractor to video record the underdrain outlet prior to paving.
    • Required traffic control measures, proximity of traffic to the work area, and maintaining driveways during construction.
    • How they intend to prevent contamination of existing material during trenching operations.
    • 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.

In some instances, the plans may detail the intended outlet locations, a review of the plans is warranted.

Sample Plan Sheet indicating Outlet Locations

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CONSTRUCTION

The plans show the underdrain alignment within the typical roadway section. Trench width and depth can vary based on the size of the pipe used. Refer to the plans and Standard Plan R-80 series for trench width details. All underdrain must be installed with a continuous grade to ensure there are no high or low points. No contamination of other roadway layers should occur during underdrain installation.

Bank Underdrain

When slopes have significant runoff or seepage, underdrain will be installed in the bank to collect water and prevent slope erosion. Typically, the first bank underdrain run is installed at the top of the bank, with additional runs spaced out throughout the bank. The amount and spacing of subsequent runs depends on total water runoff and seepage. Installation begins with excavation of the trench in accordance with the plan locations. The bottom of the trench should be formed to the shape of the pipe. Pipe installation typically includes a wrapped underdrain pipe being placed at the bottom of the trench before being backfilled with granular material Class II AA and compacted. Caution needs to be used during compaction of the backfill to ensure the pipe is not damaged while compacting the backfill material.

An open-graded version of bank underdrain can be installed. This includes:

  1. Lining the trench with a geotextile blanket.
  2. Placing 1 to 2 inches of backfill below the underdrain pipe.
  3. Placing a nonwrapped underdrain pipe.
  4. Backfilling with open-graded aggregate Class 34R.

Subgrade Underdrain

Subgrade underdrain is installed beneath the shoulder of the roadway to a depth of 5 feet below the surface of the shoulder and 4 feet from the edge of the travel lane. The bottom of the trench should be formed to the shape of the pipe. A wrapped underdrain pipe is placed in the bottom of the trench before being backfilled with granular material Class II AA and compacted. Caution needs to be used during compaction of the backfill to ensure the pipe is not damaged while compacting the backfill material.

An open-graded version of subgrade underdrain can be installed. This includes:

  1. Lining the trench with a geotextile blanket.
  2. Placing 1 to 2 inches of backfill below the underdrain pipe.
  3. Placing a nonwrapped underdrain pipe.
  4. Backfilling with open-graded aggregate Class 34R.

Subbase Underdrain

Subbase underdrain is installed a maximum of 10 inches below the top of the subgrade either under the roadway or shoulder. If installed under the roadway, the placement is typically designed to not be under a wheel path of traffic. Once the trench is excavated and the bottom of the trench formed to the shape of the pipe, wrapped underdrain pipe is placed in the trench. Granular material Class II AA is placed as backfill around the pipe and to the top of the trench. A minimum of 2 inches of cover from the top of the underdrain pipe to the bottom of the subbase must be obtained. Caution needs to be used during compaction of the backfill to ensure the pipe is not damaged while compacting the backfill material.

Subbase Underdrain Pipe Installed in Trench

Open-Graded Underdrain

Open-graded underdrain is installed within the subgrade with the top of the trench at the same elevation as the top of the subbase in the roadway or shoulder. Be sure not to get this confused with the other types of underdrain, which have open-graded variants. There are 2 main types of open-graded underdrain: with geotextile separator or with dense-graded aggregate as a separation layer. Refer to the Standard Plan R-80 series for more details on open-graded underdrain installation.

  1. With a geotextile separator refers to a geotextile separator being placed between the subbase and OGDC layers of a roadway. Before placing the geotextile separator on top of the subbase, the open-graded underdrain is installed. The trench is excavated through the subbase and into the subgrade forming the bottom of the trench to the shape of the pipe. A geotextile blanket is placed to line the trench before the nonwrapped underdrain pipe is placed. The geotextile blanket should overlap the top of the trench a minimum of 1 foot. Ensure 1 to 2 inches of 34R backfill material is placed under the pipe before the remainder of the trench is filled. There will be 2 to 3 inches of 34R backfill material placed over the top of the trench to 6 inches beyond the edge of the trench.
  2. With a dense-graded aggregate refers to a dense-graded aggregate layer being placed between the subbase and open-graded aggregate base layers of the roadway. Before the open-graded aggregate base layer is installed, the open-graded underdrain must be installed. The trench is excavated through the dense-graded aggregate base, the subbase, and into the subgrade forming the bottom of the trench to the shape of the pipe. A geotextile blanket is placed to line the trench before the nonwrapped underdrain pipe is placed. The geotextile blanket should overlap the top of the trench a minimum of 1 foot. Ensure 1 to 2 inches of open-graded aggregate Class 34R backfill material is placed under the pipe before the remainder of the trench is filled. There will be 2 to 3 inches of 34R backfill material placed over the top of the trench to 6 inches beyond the edge of the trench.
centerOpen-Graded Pipe in the Lined Trench
34R Backfill Place in the Open-Graded Underdrain Tench

Outletting Underdrain

Outlet locations should be in accordance with the plans or the Standard Plan R-80 series, at all low points and should not exceed 300-foot spacing between outlets. At outlet locations, a 5-foot section of the perforated pipe is bent to form an arc in accordance with Standard Plan R-80 series prior to transitioning to the solid outlet pipe. The use of wyes or tees is prohibited. Connections between underdrain and outlet pipes should be in accordance with the manufacturer’s recommendations or by Engineer approval. If the outlet is tapped into a drainage structure, the cored or sawed hole in the structure should be sealed with brick and mortar. When draining to a roadside ditch, outlets should be run at minimum of 4% grade and maintain 4 inches of freeboard above the ditch invert. The outlet pipe installed should be either corrugated metal pipe or PVC with the corresponding concrete or metal outlet endings. The percent grade can be adjusted to meet outlet elevation requirements. Outlet ending locations should be marked on the shoulder of the road with a stencil as well as a drainage marker post. Metal end sections are not permitted on PVC outlet pipe.

centerPVC Outlet for Subbase Underdrain
Underdrain Outlet Tapped into a Drainage Structure

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INSPECTION & TESTING

Inspection

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

  • Measuring wheel
  • 100-foot tape measure or longer
  • 25-foot tape measure
  • Chaining pin
  • 6-foot stick ruler
  • 4-foot level
  • Working plans
  • String line or laser level if traditional survey stakes are used
  • Camera
  • Survey equipment

The Inspector should take the following steps during construction:

  1. Check the trench dimensions to ensure the Contractor is meeting the specification requirements.
  2. Monitor the trenching operation to ensure cross-contamination of other materials does not occur.
  3. Inspect the underdrain pipes for proper alignment, grade, and placement within the trench. Ensure the pipes are securely connected and any required fittings or joints are properly installed.
  4. Examine the backfill material surrounding the underdrain pipes to ensure it meets the specified gradation and compaction requirements. Verify the backfill is uniformly compacted in layers to provide adequate support and stability to the underdrain system.
  5. Obtain material tickets.
  6. If geotextile blanket is specified in the design, inspect the installation to ensure it is properly installed prior to placement of the backfill material. Verify the fabric is securely fastened and overlaps correctly to serve as an effective filter.
  7. Verify the installation of end caps on the upstream end or outlets and outlet ends at the ends of the underdrain system. Cutting the underdrain pipe and folding the end or tying the end of the sock are not approved methods for capping the end of the underdrain. Ensure end sections provide a smooth transition for water flow and outlets are positioned to discharge water away from the roadway.

Video Inspection

All underdrain must be video inspected in accordance with the Special Provision for Video Inspection of Underdrain (20SP-404A-01). The Inspector is required to witness the Contractor record the video of the underdrain as a copy of the video is not provided. The arc of the underdrain for outletting purposes should not be greater than 90 degrees to allow the camera to be pushed past the outlet into the mainline run of underdrain. The purpose of the video inspection is to identify any installation defects in the underdrain pipe/underdrain outlet pipe such as:

  • Crushed pipe.
  • Separated joints.
  • Plugged underdrain and/or underdrain outlet pipe.
  • Standing water exceeding half the pipe diameter for a distance of 25 feet or more.
  • Other anomalies.

The video inspection of open-graded underdrain should be performed after the mainline pavement is placed but before the shoulder is paved. Underdrain should be video inspected, including open-graded underdrain, prior to pavement placement if located under pavement but after placement of the aggregate base. The underdrain outlets, including outlet endings, must be completely installed prior to conducting the video inspection. Defects found must be excavated and repaired, and/or removed and replaced, via a method proposed by the Contractor and meeting the Engineer’s prior approval.

Underdrain Inspection

Common problems with underdrain installation have been observed in the past. The Inspector should take the following steps when inspecting underdrain:

  • For open-graded underdrain, ensure the geotextile separator is not placed over an open-graded underdrain trench (on projects where geotextile separator is called for between the sand subbase and open-graded drainage course). This does not allow the system to function correctly.
  • Verify there are no improper connections made within the outlet pipe. If connections are required in the outlet pipe, they must be watertight, and the connectors must be of the same material as the outlet pipe (e.g., rigid PVC outlet pipe needs connections made with rigid PVC connectors).
  • Confirm the use of properly sized concrete rings (when Concrete Ring Option for outlet endings is used). The Standard Plan R-80 series calls for 3-foot lengths for the concrete rings and 2-foot lengths have been incorrectly installed in the past. If concrete end sections are used, they are typically 2 feet in length.
  • Verify there are no sags in the underdrain pipe just before it connects to the underdrain outlet pipe.

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.

For every new source, new day, or suspected change in material, a moisture check needs to be completed. Obtaining moisture readings from a nuclear density gauge is an acceptable method to gauge moisture results of material in the field. Final determination of moisture content will be made from a field sample stored in a plastic bag with the moisture content checked for payment using the oven dry method only if it’s paid for by weight.

Density for each lift needs to be achieved before subsequent layers are built up. The maximum lift thickness permitted is 12 inches after compaction. For foundation, bank, subbase, and subgrade underdrains and outlets within the influence of the roadbed, density needs to achieve a minimum of 95% compaction. The Inspector should ensure the minimum number of required density tests are being performed per the Density Testing and Inspection Manual.

Geosynthetic materials must be tested according to the Materials Quality Assurance Procedures (MQAP) Manual prior to installation on the project. The Inspector should work with the testing agency to obtain a sample prior to installation of the material. Geotextiles must be unwrapped one full roll circumference prior to sampling. All samples must be rolled, not folded, during shipment to prevent creases in the fabric.

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MEASUREMENT, DOCUMENTATION & PAYMENT

Measurement and Payment

Underdrains are measured in place by length in feet along the centerline of the underdrain. Inspector should note starting and stopping stations and the station of the outlets.

Documentation

The primary report required for the payment of underdrains 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. Sketches and calculations documenting the work is completed is required and should include:

  1. Station to station length and trench width being paid on this date.
  2. Survey or other approved methods for verification the underdrain was constructed in conformance with the project documents.
    • Collecting the GPS location of all underdrain outlets for as-built plans is good practice.
  3. Volume and tonnage of material placed.

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 Materials 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

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RAIL PROJECTS

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