Article 1 — Description
Install pipe underdrains.
Article 2 — Materials
2.1 Pipe . Furnish the types and sizes of pipe shown on the plans. Use only one type of pipe for any underdrain
system on the project. Use perforated pipe in areas to be drained and use non- perforated pipe between the perforated pipe and the outfall.
2.1.1 Type 1. Corrugated steel pipe (CSP) conforming to any type specified in AASHTO M 36, fabricated from
corrugated galvanized sheet.
2.1.2 Type 2. Corrugated aluminum pipe conforming to AASHTO M 196, Type I or Type IA, fabricated from
corrugated sheet.
2.1.3 Type 3. Bituminous -coated CSP conforming to the requirements of Type 1 and uniformly coated inside and
out with a minimum thickness of 0.05 in. of bituminous material meeting the requirements shown in Table 1 when tested in accordance with ASTM A849 Material Class A or Material Class PA. Table 1 Requirements of Bituminous Material Test Requirements Solubility, % by wt., in trichloroethylene 99.5 Min Brittleness Pass Flow, in. 0.25 Max
2.1.4 Type 4. Bituminous -coated corrugated aluminum pipe conforming to the requirement s of Type 2 and
uniformly coated inside and out with a minimum thickness of 0.05 in. of bituminous material meeting the requirements shown in Table 1 when tested in accordance with ASTM A849 Material Class A or Material Class PA .
2.1.5 Type 6. Corrugated polyethylene plastic tubing conforming to AASHTO M 252.
2.1.6 Type 7. Corrugated polyvinyl chloride (PVC) pipe conforming to ASTM F949.
2.1.7 Type 8. Smooth- wall PVC pipe conforming to AASHTO M 278 Class PS 46.
2.1.8 Type 9. As shown on the plans.
2.2 Filter Material. Furnish hard, durable, and clean sand, gravel, crushed stone, or crushed shell meeting the
gradation by percent weight shown in Table 2 unless otherwise shown on the plans. Filter material must be free of clay balls or other organic or deleterious matter as determined by in accordance with Tex-413-A. Use of crushed limestone is allowed unless otherwise shown on the plans. Use only one type of filter material for any underdrain system on a project. 836 Table 2 Acceptable Gradations for Filter Material Sieve Size Type B Type C Type E Type F Type G % Retained on Sieve ( Tex-401-A) Grade 2 Coarse Aggregate2 Grade 3 Coarse Aggregate2 Grade 4 (57) Coarse Aggregate2 1-1/2″ – 0–10 3/4″ 0–10 20–40 3/8″ 15–35 – #4 35–55 40–60 #20 35–651 35–651 #50 75–1001 75–1001 1. Of the portion finer than No. 4 sieve. 2. Refer to Table 4 in Item 421, “Hydraulic Cement Concrete .” Loss by decantation as determined by in accordance with Tex-406-A must not exceed 1% of the material retained on a No. 4 sieve or 4% of the material passing a No. 4 sieve. Use Type G filter material around the underdrains unless otherwise shown on the plans.
2.3 Filter Fabric. Meet DMS -6200 , “Filter Fabric,” Type 1.
2.4 Riprap . Provide concrete riprap in accordance with Item 432, “Riprap,” when required.
Article 3 — Construction
Begin excavation of the trench at the outfall and proceed toward its upper end, following the lines and grades shown on the plans or as directed. Hold the minimum horizontal limits of excavation for filter material to the dimensions shown in Table 3 or as shown on the plans. Table 3 Minimum Horizontal Limits of Excavation for Filler Material Depth of Trench (ft.) Distance Outside Neat Lines of Pipe Underdrains (ft.) 0–6 1.00 >6–10 1.50 >10–15 2.00 >15 2.50 Place filter fabric in the bottom and sides of the trench in areas to be drained before placing pipe or filter material, as shown in Figure 1. Provide enough width of fabric to overlap on top of the filter material. Center perforated pipe in the excavated ditch with the perforations below the horizontal axis. Join the pipe with appropriate couplers if required. Join plastic pipe in conformance with the manufacturer’s recommendations. Do not use tarpaper strips. Obtain approval for pipe placement before placing filter material. Place filter material at least 12 in. above the bottom of the pipe or as shown on the plans. Do not allow filter material to displace the pipe. Lap filter fabric over the top of the filter material after placing pipe and filter material in conformance with the manufacturer’s recommendation or as shown on the plans. Figure 1 Installation Process Install non- perforated pipe sections between the perforated pipe and the outfall. The sections of non-perforated pipe do not require filter fabric or filter material. Place approved plugs in the upper ends of all pipe. Cover exposed outfall ends with 1/2- in. galvanized hardware cloth as directed. Provide Class B concrete riprap, when required, in accordance with Item 432 and as shown on the plans. Place the riprap to the contour and grade of the embankment slope. Cut the pipe to the slope of the riprap. Backfill the remainder of the trench with suitable material in layers not to exceed 6 in.
Article 4 — Measurement
This Item will be measured by the foot along the top of the pipe and will include the length of elbows, wyes, tees, and other branches.
Article 5 — Payment
The work performed and material furnished in accordance with this Item and measured as provided under “Measurement” will be paid for at the unit price bid for “Pipe Underdrains” of the pipe type and size specified. This price is full compensation for pipe, couplers, plugs, screens, filter material, filter fabric, riprap, excavation, backfill, equipment, labor, materials, tools, and incidentals. Protection methods for excavations deeper than 5 ft. will be measured and paid for in accordance with Item 402, “Trench Excavation Protection.”