SECTION 703 — UNDERDRAINS AND COMBINATION DRAINS 700-17 — UNDERDRAINS AND COMBINATION DRAINS
703.01 Description.
This work includes constructing underdrains and/or combination drains in reasonably close conformity with the required dimensions and details.
703.02 Materials.
Pipe. Ensure that the following types of pipes conform to SECTION M04: • Perforated concrete pipe (Subsection M04.01.3) • Perforated corrugated polyethylene drainage pipe (Subsection M04.01.5) • Perforated corrugated polyvinyl chloride pipe (Subsection M04.01.6) • Perforated, smooth interior, high-density polyethylene (HDPE) pipe (Subsection M04.01.7) Filter Fabric. Use a filter fabric material suitable for underdrain and combination drain applications. Ensure that the material complies with Subsection M20.01. Do not use heat set or heat calendared fabrics. Filter and Bedding Materials. Use filter stone, fine aggregates, and bedding stone that conform to SECTION M01. Use gravel sump /filter stone that conforms to Subsection M01.07 and Subsection M01.09, Column V of the Table. Impermeable High-Density Polyethylene (HDPE) Liner. Use impermeable plastic liner that is nonwoven high-density polyethylene (HDPE) liner specifically designed for use in subsurface lining/containment applications. Ensure that the liner complies with Subsection M04.01.8. Ensure that the liner has been fabricated and delivered in rolls, not sheets. To keep the number of overlay joints to a minimum, provide the liner in sections not less than 15 ft in width, unless otherwise approved by the Engineer before delivery on site.
703.03 Construction Methods.
General. Construct the specified sizes and types of underdrains and/or combination drains according to the required lines and grades. Do not interchange or interconnect the various types of pipe except through the introduction of appropriate manholes or catch basins.
Part 700 — Drainage and Selected Utility Accessories August 2025
700-18 SECTION 703 — UNDERDRAINS AND COMBINATION DRAINS Ensure that manholes and catch basins required for underdrain and/or combination drain installation conform to SECTION 702. Installation of Pipe.
a.Layout. Ensure that the pipe layout conforms to Subsection 701.03.1.
b.Trench Excavation. Excavate trenches according to the SECTION 205. Extend the trench excavation to the required width, or as directed by the Engineer, to allow for the compaction of both the bedding and backfill material under and around the pipe. Ensure that the trench walls are either vertical or as near vertical as conditions permit.
c.B edding and Filter Fabric . Place a bedding layer of specified filter stone, fine aggregate, or filter fabric within the trench for its full width and length.
d.Lay ing Drains . Embed underdrains and combination drains firmly in the filter stone. Place perforated pipe with the perforations down for underdrains and up for combination drains. Join the pipe with the appropriate coupling fittings or bands. Close the upgrade ends of all underdrain pipe with plugs to prevent entry of soil materials. After the pipe installation has been inspected and approved, place filter stone to the required height above the top of pipe. Fill any remaining portion of trench above the filter stone with fine aggregate as specified. Compact t he fine aggregate using moderate compactive effort by making two passes with a vibratory compactor.
e.Outlets. Place outlet pipes in trenches with all ends securely jointed as recommended by the pipe manufacturer. After inspection of the outlet pipe installation by the Engineer, backfill the trench with material meeting the applicable requirements of SECTION M01. Place the material in 12 -in. layers and compact with moderate compactive effort with vibratory equipment. Unauthorized Excavation. If the bottom of any trench has been excavated below the required grade, restore the bottom to grade by refilling with a well-compacted bedding material as selected by the Engineer in writing.
703.04 Method of Measurement.
Underdrain and Combination Drain, including their outlets, will be measured in the linear feet as installed.
703.05 Basis of Payment.
The Department will pay for the completed and accepted quantities as follows.
Part 700 — Drainage and Selected Utility Accessories August 2025
SECTION 703 — UNDERDRAINS AND COMBINATION DRAINS 700-19 Pay Item Pay Unit Underdrain LF Combined Drain LF The Contract prices constitute full compensation for all labor, materials, and equipment for providing the underdrains and combination drains including all trench excavation (except Trench Excavation – Rock and Trench Rock Excavation/Mechanical), bedding, filter stone, filter fabric, placing and compacting backfill, and all incidentals required to finish the work, complete and accepted. Trench Excavation – Rock and Trench Rock Excavation – Mechanical will not be included in the Contract unit prices for underdrains and combination drains but will be paid for separately as set forth in Subsections 205.04.2 and 205.05.1. No payment will be made for unauthorized excavation. Furnish, place, and compact the bedding material used to refill the trench to grade at no additional cost to the Department.
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Source: Standard Specifications for Road and Bridge Construction (Blue Book), 2022 (Aug 2025 compilation) Edition. Pages 342–344 of 951. View official source ↗