2502.01 DESCRIPTION.
Construction of subdrains shall consist of furnishing and installing subdrain of the size and type shown in the contract documents. All subdrains shall be installed at the locations and to the grades and elevations shown in the contract documents. This work shall also include the construction of trench drains. The provisions of Section 2403 shall apply.

2502.02 MATERIAL.
Pipe for subdrains shall be of the size and type shown in the contract documents and shall meet requirements of Section 4143.

Engineering fabric, when required, shall meet the requirements of Article 4196.01,B.

Porous backfill material shall meet requirements of Section 4131.

Corrugated Metal Pipe Subdrain Outlet shall meet the requirements of Section 4141.

2502.03 PLACING STANDARD SUBDRAINS.
Construction of standard subdrains shall begin at the outlet and proceed continuously upgrade unless the Engineer grants permission to construct the drain in sections. The Engineer will furnish stakes and figures for the grade of the flow line, and the pipe shall be set accurately to line and grade. When used, the ends of drain tile shall be laid as closely together as possible. Junctions in lines of tile shall be made with special tile connections. When a change in diameter of pipe is greater than 2 inches (50 mm), a special connection shall be used. Joints in metal and plastic pipe shall be made with properly fitting connectors. Junctions of lines of pipe shall be made with properly designed fittings. When existing tile lines are encountered, all necessary precautions shall be taken to prevent damage to them. Such tile lines shall be connected to the subdrain being installed.

Inlets to subdrains shall be constructed by filling the full width and depth of the trench for the length specified with porous backfill material.

Intakes shall be constructed in accordance with the design and locations specified. Construction of intakes shall include placing the pipe through the wall of the intake structure.

Pipes shall not be covered until they have been inspected by the Engineer.

Except when porous backfill material is specified, the pipe shall be carefully covered (blinded) to a depth of approximately 6 inches (150 mm) with soil or other approved material. Sand or boulders shall not be placed directly against the pipe. After the drain has been blinded, the remainder of the trench shall be backfilled by methods and materials approved by the Engineer.

When subdrains are placed beneath a highway or driveway or within 5 feet (1.5 m) of the edge of an existing or proposed pavement or base course, backfill material shall be placed in layers not over 6 inches (150 mm) in thickness, and each layer shall be thoroughly tamped with mechanical tampers.

The contract documents may also require construction of a granular blanket in connection with subdrains, in which case the granular blanket shall be constructed according to Article 2107.11.

When installation of a granular blanket is required, the Contractor shall place porous backfill for subdrains prior to construction of the granular blanket.

All subdrain outlets shall be marked with a steel post. The post shall meet the requirements of Article 4154.09. The Contractor shall drive the post 3 feet (1 m) into the ground and install a 4 foot (1.1 m) plastic sleeve over the post. When sleeves are furnished by the Contracting Authority, the Contractor shall install them. Only one post shall be required to mark the location of a double outlet.

Excess excavated material shall be used on the project or removed from the project as directed by the Engineer.

2502.04 TRENCH DRAINS.
Trench drains shall be constructed at the locations, depth, and grade shown in the contract documents or as directed by the Engineer.

The trench shall be filled with uncompacted porous backfill.

2502.05 PLACING LONGITUDINAL SUBDRAINS.
Continuous longitudinal subdrains shall be placed as indicated. Outlets through the shoulder shall be installed as shown in the contract documents at approximately 500 foot (150 m) intervals. Additional outlets shall be provided at the low point of sag in vertical curves. Outlet locations may be adjusted by the Engineer. The outlet end of each subdrain shall be covered with the specified outlet covering, and the blind end shall be capped with a fitting recommended by the manufacturer. Class A crushed stone shall be placed over porous backfill at piers and at subdrain outlets as shown in the contract documents, and this material shall be well compacted by tamping or vibration. Other outlets may be by special connections which will be shown in the contract documents.

The elongation of the polyethylene tubing shall not exceed 5%.

Longitudinal and lateral shoulder subdrains shall be constructed as shown in the contract documents. The aggregate for backfill shall be wetted prior to installation, and a surface application of water may be required by the Engineer. The aggregate for subdrain backfill shall be placed in accordance with the following:

A. For a 24 inch (0.6 m) depth subdrain trench, the aggregate used for subdrain backfill shall be placed in one lift above the subdrain pipe. The lift shall be compacted with a vibratory compactor, narrower than the trench to maximum consolidation.

B. For a 36 inch (0.9 m) depth subdrain trench, the aggregate used for subdrain backfill shall be placed in one lift above the subdrain pipe. The lift shall be compacted with a vibratory compactor and an approved trench roller, narrower than the trench, to maximum consolidation.

C. For a 42 inch (1.1 m) or greater depth subdrain trench, the aggregate for subdrain backfill shall be placed in two lifts of approximately equal thickness above the subdrain pipe. The first lift shall be compacted with a vibratory compactor narrower than the trench. The second lift shall be compacted with a vibratory compactor and an approved trench roller, narrower than the trench, to maximum consolidation. It is intended that the compaction provided for longitudinal subdrains shall not damage the subdrain pipe. When the thickness of porous backfill immediately above the subdrain is less than 1 foot (0.3 m), the aggregate shall be placed in one lift and compacted with a vibratory compactor.

Maximum consolidation will be determined by an initial trial section, approximately 100 feet (30 m) long. Compaction shall continue on this section until maximum consolidation is achieved. The backfill material, together with any engineering fabric which may be included in the design, shall be kept protected and undisturbed during subsequent pavement removal, concrete placement, or other work, so as to prevent intrusion of foreign material into the porous backfill. Trench rollers shall have a minimum trench wheel weight (mass) of 6,000 pounds (2700 kg).

Shoulder subdrain work shall include restoration of the shoulder and foreslope area. Unpaved shoulders shall be finished with a minimum depth of 4 inches (100 mm) of granular shoulder material. Granular shoulder material or earth shall be compacted with a minimum of three passes with a single vehicle tire loaded to 6,000 pounds (2700 kg). Shoulders paved with HMA or at designated locations shall be finished with a minimum depth of 6 inches (150 mm) of HMA base, Class 1, (Section 2203) or better. The edges shall be tacked, and the HMA base mixture placed and compacted in an initial 4 inch (100 mm) lift and a final lift which restores the surface flush with and not more than 1/4 inch (5 mm) above the adjacent pavement surface. Each lift shall be thoroughly compacted with a minimum of three passes with a single vehicle tire loaded to 6,000 pounds (2700 kg) and no wider than the trench, or by equivalent compaction with an approved trench roller.

If evidence of paved shoulder settlement occurs prior to completion of the project, the Contractor will be required to proof roll those areas. Proof rolling shall be done by a single vehicle tire no wider than the subdrain trench and loaded to 6,000 pounds (2700 kg). Settlements greater than 1/4 inch (5 mm) shall be corrected. Correction shall be with a 3/8 inch (9.5 mm) mixture described in Section 2203, or a similar commercial mixture approved by the Engineer. The surface shall be tacked, and the mixture shall be spread and compacted. Compaction shall be subject to approval of the Engineer, and it may be accomplished with loaded truck tires.

If a large boulder or obstruction other than a culvert is encountered, the subdrain shall be constructed as shown on the detail for trench repair at culverts, except the engineering fabric and 1 foot (0.3 m) of compacted earth are not necessary. An additional subgrade outlet will be necessary for the interrupted drainage.

Culverts and other facilities owned by the Contracting Authority shall be repaired as directed by the Engineer if they are damaged by trenching equipment.

When subdrains are constructed on existing roads, and when removal of the excavated material is required, the excavated material shall be loaded directly into the transporting vehicle. The contract documents may designate an area to place this material. If an area is not designated and the Engineer does not designate one, the Contractor shall remove the excavated material from the project in accordance with Article 1104.08.

Backslope subdrains shall be constructed as shown in the contract documents. The aggregate may be placed in one lift and with no compaction. The remaining trench shall be filled and mounded with earth in one lift, and the earth shall be compacted in place. The earth covering shall be leveled to match the adjacent area.

Subdrains at piers shall be covered with granular material described in Article 2502.02, as shown in the contract documents, after the porous backfill is placed and compacted. The granular material shall be compacted in the same manner as the porous backfill.

All subdrain outlets shall be covered with a rodent guard described in Article 4143.01, B. All subdrain outlets, except for medians, shall be marked with a steel post meeting the requirements of Article 4154.09. The Contractor shall drive the post 3 feet (1 m) into the ground and install a 4 foot (1.1 m) plastic sleeve over the post. When sleeves are furnished by the Contracting Authority, the Contractor shall install them. Only one metal fence post willbe required to mark the location of a double outlet.

2502.06 LIMITATIONS.
When the work is completed, all subdrain outlets shall be open and free of debris.

When the road is open to public traffic during construction, work or uncompleted work must be within the limits of a traffic control zone.

2502.07 METHOD OF MEASUREMENT.
Subdrain construction will be measured as follows:

A. Standard Subdrain.
The length of standard subdrains of the various types and sizes specified will be measured to the nearest foot (meter) along the center line of the subdrain.

B. Longitudinal Subdrain.
The Engineer will compute, to the nearest foot (meter), the lengths of longitudinal subdrain from the following:

1. Longitudinal Subdrain (Backslope).
The lengths of backslope subdrains of each size, including lengths of subdrain placed in laterals and outlets, and the extension into the outlet pipe will be measured.

2. Longitudinal Subdrain (Shoulders).
The lengths of each size of shoulder subdrains and subdrains at piers will be calculated from centerline stationing. The lengths of perforated subdrains in laterals and outlets, including the extension into the corrugated pipe, will be measured.

C. Subdrain Outlet.
The Engineer will count the number of subdrain outlets installed, of the size specified.

D. Intakes.
The Engineer will count the number of intakes installed of the size and type specified.

E. Trench Drain.
The Engineer will measure, to the nearest foot (meter), the length of trench drain constructed.

2502.08 BASIS OF PAYMENT.
Payment for subdrain construction will be as follows:

A. Standard Subdrains.
For the number of linear feet (meters) of standard subdrain of the size specified, furnished, and placed, the Contractor will be paid the contract unit price per foot (meter).

This payment shall be full compensation for trenching, removal of excess excavated material from the project, furnishing and placing end caps, elbows, tees, and other necessary connections and furnishing and placing porous backfill where specified. It shall also include backfilling the trench and finishing the surface as directed by the Engineer and all tools and labor necessary to construct the subdrain.

For subdrains built in accordance with the contract documents, no extra compensation will be allowed for overdepth, rock excavation, tamping backfill, and removal of surplus material from the project.

When the contract documents do not indicate the depth of excavation, the first 6 feet (1.8 m) of excavation will be included in the contract unit price. Payment will be made for overdepth excavation in accordance with Article 2503.05.

B. Longitudinal Subdrains.

1. Longitudinal Subdrain (Backslope).
For the number of linear feet (meters) of longitudinal subdrain (backslope) of each size placed, the Contractor will be paid the contract unit price per foot (meter).

2. Longitudinal Subdrain (Shoulder).
For the number of linear feet (meters) of longitudinal subdrain (shoulder) of each size placed, the Contractor will be paid the contract unit price per foot (meter).

Payment for longitudinal subdrains shall be full compensation for excavation of the trench, and removal of excess trench material from the project, furnishing and placing subdrain pipe, laterals, elbows, tees, special connections, couplings, and adaptors in accordance with the manufacturer's recommendations; furnishing and placing porous backfill; furnishing and placing engineering fabric as required; restoring the shoulder of shoulder subdrains and covering backslope subdrains with earth, including shoulder outlet locations; and for proof rolling as specified.

When boulders result from excavation for longitudinal subdrains, the Engineer may order boulder pickup and removal from the project. When ordered, payment for this work will be at 10 (4) times the contract unit price for placing the longitudinal drains on the backslope or shoulder as appropriate, per cubic yard (cubic meter) of boulders.

C. Subdrain Outlet.
For each subdrain outlet installed, the Contractor will be paid the contract unit price. This payment shall be full compensation for furnishing and installing corrugated metal pipe, double walled PE, or PVC pipe; including the outlet coverings, grouted joints and special connections, drilling or forming into an existing drainage facility, and associated excavation, backfill with specified material, furnishing and installing steel post and concrete patio block, installing plastic sleeve, and restoration of the site.

D. Intakes.
For the number of intakes constructed, of the size and type specified, the Contractor will be paid the contract unit price. This payment shall be full compensation for all materials, labor, and equipment necessary for construction of the intakes, as specified, including excavation and removal of excess material from the project.

E. Trench Drain.
For the number of linear feet (meters) of trench drain constructed, the Contractor will be paid the contract unit price per foot (meter). This payment shall be full compensation for trenching, removal of excess excavated material from the project and furnishing and placing porous backfill.