4-32 Section 404. Underdrains
404.01. Description This work consists of constructing and installing underdrains, foundation underdrains, and underdrain outlets. 404.02. Materials Provide materials in accordance with the following sections : Granular Material Class II AA ................................................................ 902 Open-Graded Aggregate 34R ............................................................... 902 End Sections ......................................................................................... 909 Pipe for Underdrains ............................................................................. 909 Underdrain Outlets ................................................................................ 909 Drainage Marker Posts ......................................................................... 909 Sod ....................................................................................................... 917 Topsoil ................................................................................................... 917 Mortar, Type R -2 ................................................................................. 1005
A.Pipe. Provide geotextile-wrapped perforated pipe and tubing for underdrains, except if using with open-graded backfill material. Provide non-perforated pipe and tubing not wrapped with geotextile for underdrain outlets. Provide the following slot or hole size and water inlet area for pipe if using steel furnace slag for open-graded drainage course. Table 404- 1: Pipe Opening Sizes for Steel Furnace Slag Open -Graded Drainage Course Opening Type Size Slot width 1/16 – ⅛ inch Hole diameter ⅛ – 3/16 inch Water inlet area (min) 2 in²/ft of tubing
B.Aggregate for Trench Backfill. Provide open-graded aggregate 34R to backfill the trench for open- graded underdrain. Provide granular material Class II AA as backfill for other underdrains and underdrain outlets.
C.Outlet Endings. Provide a concrete ring, steel end section, or concrete end section for the outlet ending. 404.03. Construction The plans will show the locations for underdrain and underdrain outlets or will establish a miscellaneous quantity of pipe for use on t he project. The plans will show, or the Engineer will determine, the line and grade of the MDOT Standard Specifications for Construction Section 404
4-33 underdrain. Place the outlets at the intervals shown on the plans and ensure
that the outlets drain.
A.Trench Excavation. Excavate underdrain trenches using a wheel or chain trencher or other trenching method approved by the Engineer. Grade trench bottoms to the shape of the underdrain pipe. Line trenches for open- graded underdrains with geotextile blanket as required.
B.Laying Underdrains. Place the underdrains to the line and grade shown on the plans or established by the Engineer. Ensure a firm bearing along the length of the pipe. Place compatible end caps on the upgrade ends of the underdrain pipes. Remove and re-lay damaged or displaced pipe.
C.Connections . Select fittings and connection methods in accordance with the underdrain system manufacturer ’s recommendations to prevent pipe separation. Do not penetrate the inside diameter of the pipe with the self -tapping screws by more than ⅛ inch. Wrap fittings with geotextile blanket and seal the geotextile to the outlet pipe with waterproof tape.
D.Backfill and Compaction. Place backfill in trenches after the Engineer approves the underdrain line and grade.
1.Foundation, Bank , Subbase and Subgrade Underdrains, and Underdrain Outlets . Backfill using granular material Class IIAA . Place the granular material around the pipe to cover the drain with at least 12 inches of material. Place the remaining backfill in layers no greater than 12 inches. Compact the trench backfill material within the influence of the roadbed to 95 % of the maximum unit weight. Compact trenches outside the roadbed as directed by the Engineer. If the contract calls for open- graded subgrade underdrain and open-graded bank underdrain, place the open-graded aggregate 34R as shown on the plans for open-graded underdrains.
2.Open -Graded Underdrains . Backfill pipe with open- graded aggregate 34R. After placing the backfill, c ompact the backfill and the surrounding grade material with a vibrating plate compactor. Begin compaction along the shoulder side of the underdrain and progress toward the pavement. Do not operate the compactor directly above the underdrain. Maintain the expo sed underdrain and backfill to prevent contamination. Remove and replace contaminated backfill material as determined by the Engineer at no additional cost to the Department. Clear obstructed MDOT Standard Specifications for Construction Section 404
4-34 underdrain as determined by the Engineer at no additional cost to the
Department.
E.Underdrain Outlet. Lay underdrain outlets on at least a 4% grade and install the underdrain outlet at least 4 inches above t he receiving ditch or sewer flow line. The Engineer may waive the percent grade requirement if determining that it is not practical to meet both the percent grade and the outlet elevation requirements . Connect underdrain outlet pipe to the underdrain in ac cordance with MDOT Standard Plan R -80 series . The use of wyes, tees , or other similar fittings is not acceptable. Do not backfill the outlet trench until approved by the Engineer. Install underdrain outlets within 48 hours of installing adjoining longitudi nal underdrains. Mark and maintain the outlets until final acceptance of the work .
F.Outlet Endings . Place the outlet endings as shown on the plans or as directed by the Engineer. Install drainage marker posts in accordance with subsection 401.03.F . Mark the locations of outlet endings on the adjacent shoulder if i nstalling underdrains in conjunction with constructing or resurfacing concrete or HMA shoulders. Mark locations with a ½ -inch -deep, 4- by 6-inch depression. Place the long edge of the depression perpendicular to the edge of the shoulder. The Engineer may approve the following alternative methods of marking locations :
1.Stencil markers in concrete shoulders after texturing.
2.Form markers in HMA shoulders during finish rolling. Obtain the Engineer ’s approval of forming method prior to beginning work.
G.Cleanout. Ensure that installed underdrains and outlets are free of silt, debris, and other delet erious material at the time of final acceptance.
H.Video Inspection of Underdrains . The Department will perform video inspection of underdrains, underdrain outlets, and outlet endings after installation is complete. The Department will p erform video inspecti ons of open-graded underdrains after the mainline pavement placement is complete but before shoulder paving. Submit a log detailing the locations of the drain outlets installed on the project to the Engineer. In the drain outlet log , include locations of bank drain outlets, subgrade and subbase underdrain outlets , and open-graded underdrain outlets.
1.Deficiencies. Corrective action, including excavatin g and repair ing or remov ing and replac ing the underdrain or underdrain outlets, will be requir ed if video inspection reveals any of the following deficiencies: MDOT Standard Specifications for Construction Section 404
4-35 a. Crushed pipe;
b.Separated joints,
c.Plugged underdrain or underdrain outlet pipe ;
d.Standing water greater than half the pipe diameter for greater than 25 feet; or
e.Other defects in materials or workmanship as determined by the Engineer.
2.Corrective Action . Obtain approval from the Engineer for the repair or removal and replacement method before beginning corrective action. Complete corrective action within 10 working days of video inspection completion or other date as approved by the Engineer. Complete the following corrective action at no additional cost to the Department:
a.Excavate;
b.Repair or remove and replace defective underdrain, underdrain outlets , and outlet endings;
c.Backfill ex cavated areas;
d.Replace and compact overlying fill, aggregate base separator course, and open-graded drainage course materials;
e.Replace geotextile separator as required; and
f.Replace finished shoulder or pavement material in accordance with the contract. 404.04. Measurement and Payment Pay Item Pay Unit Underdrain, Subgrade, __ inch ......................................................... Foot Underdrain, Bank, __ inch ................................................................. Foot Underdrain, Subgrade, Open- Graded, __ inch ................................. Foot Underdrain, Bank, Open-Graded, __ inch ......................................... Foot Underdrain, Fdn, __ inch ................................................................... Foot Underdrain, Subbase, __ inch ........................................................... Foot Underdrain, Pipe, Open-Graded, __ inch .......................................... Foot Underdrain, Edge of Pavt, __ inch .................................................... Foot Underdrain Outlet, __ inch ................................................................ Foot Underdrain, Outlet Ending, __ inch .................................................. Each MDOT Standard Specifications for Construction Section 404
4-36 A. General. The Engineer will measure underdrains in place.
The Engineer will measure Underdrain Outlet , of the size required, in place from the underdrain to the center of a drainage structure or from the underdrain to the end of the outlet pipe. In addition to work specified for individual pay items, the unit prices for the relevant underdrain and underdrain outlet pay items include the cost of the following:
1.Excavating the trench;
2.Providing and placing the pipe and fittings;
3.Providing, placing, and compacting the backfill material; and
4.Disposing of surplus material excavated from the trench. The Department will not consider claims for additional compensation for time required to repair or remove and replace deficient underdrain, underdrain outlets, and overlying materials.
B.Subgrade, Bank, Foundation, and Subbase Underdrains . The unit prices for Underdrain, Subgrade ; Underdrain, Bank ; Underdrain, Fdn ; and Underdrain, Subbase of the sizes required include the cost of providing the pipe and fittings with a geotextile wrap.
C.Underdrain, Pipe, Open -Graded. The unit price for Underdrain, Pipe, Open -Graded of the size required includes the cost of providing and lining the trench with geotextile blanket .
D.Underdra in Outlet. The unit price for Underdrain, Outlet of the size required includes the cost of the following:
1.Locating installed outlets;
2.Maintaining the end of the outlet pipe or end section clear of obstructions; and
3.Providing and installing temporary tie-do wns.
E.Underdrain, Outlet Ending . The unit price for Underdrain, Outlet Ending of the size required includes the cos t of the following:
1.Excavating the area at the end of the outlet;
2.Providing and placing the concrete ring, steel end section, or concrete end section; and
3.Disposing of surplus excavated material. The Engineer will measure and the Department will pay for pipe or tubing used in or through the outlet ending as Underdrain Outlet . The unit price MDOT Standard Specifications for Construction Section 404
4-37 for Underdrain, Outlet Ending includes the cost of mark ing the outlet
ending locations on the adjacent shoulder. The Engineer will measure and the Department will pay for drainage marker posts in accordance with subsection 401.04.
Source: Michigan Standard Specifications for Construction, 2020 Edition. Pages 238–243 of 1,146.