1 Scope

NOTE This standard governs the materials, fabrication, and installation of subsurface drainage systems installed as civil and sitework elements to manage groundwater and infiltration distinct from the building foundation system. (1.1)

NOTE The work covered by this standard includes the following subdrainage applications. (1.2)

Underslab interceptor and relief drains beneath large slabs on grade — warehouse floors, pump pads, and process areas — where groundwater or construction moisture must be relieved before it reaches the slab.
Pavement subgrade edge drains and blanket drains that intercept water infiltrating through pavement joints or rising from the subgrade.
Retaining-wall and landscape-area relief drains routed through the retained-earth zone.
Athletic field and recreational area underdrains.
Interceptor drains cutting off upslope groundwater migration toward a structure or paved area.
Trench backfill drainage blankets.

NOTE The design of the subdrainage system — tributary area, pipe sizing, slope, and outlet hydraulics — is the responsibility of the geotechnical or civil Engineer of Record; this standard governs the materials and installation that execute that design. (1.3)

NOTE A building-perimeter footing drain protecting a below-grade foundation wall or basement slab is a different system with different governing requirements, and is covered by Foundation DrainageFoundation DrainageResolves to the current edition.sync/foundation-drainage; combining the two in a single specification section creates conflicting requirements and unclear responsibility. (1.4)

NOTE Site storm sewer collection and conveyance — catch basins, manholes, inlets, and outfall structures — is covered by Storm DrainageStorm DrainageResolves to the current edition.sync/storm-drainage; this standard ends at the point where the subdrainage outlet connects to that system. (1.5)

NOTE Trench excavation, structural backfill, compaction, dewatering, and temporary erosion control are covered by EarthworkEarthworkResolves to the current edition.sync/earthwork; this standard governs only the drainage envelope, pipe, and filter within the trench. (1.6)

1.7 Subdrainage system materials shall comply with this standard and with the project Contract Documents.

1.8 Where this standard conflicts with the Contract Documents or the geotechnical report, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.

2 Referenced Standards

2.1 Materials and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited in the Contract Documents.

2.2 Where referenced standards conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.

Standard	Title
ASTM F405	Corrugated Polyethylene (PE) Pipe and Fittings (3 in. through 6 in.)
ASTM F667	3 Through 24 Inch Corrugated Polyethylene Pipe and Fittings
ASTM D3034	Type PSM Poly(Vinyl Chloride) (PVC) Sewer and Drain Pipe and Fittings
ASTM D2321	Underground Installation of Thermoplastic Pipe for Sewers and Other Gravity-Flow Applications
ASTM D2412	Determination of External Loading Characteristics of Plastic Pipe by Parallel-Plate Loading
ASTM D4491	Water Permeability of Geotextiles by Permittivity
ASTM D4751	Determining Apparent Opening Size of a Geotextile
ASTM D6707	Circular-Knit Geotextile for Use in Subsurface Drainage Applications
ASTM C33	Concrete Aggregates
ASTM D2487	Classification of Soils for Engineering Purposes (Unified Soil Classification System)
AASHTO M252	Corrugated Polyethylene Drainage Pipe (4 in. to 10 in.)
AASHTO M294	Corrugated Polyethylene Pipe (12 in. to 60 in.)
AASHTO T-11	Materials Finer Than 75-µm (No. 200) Sieve in Mineral Aggregates by Washing
IBC	International Building Code (Section 1805.4, Foundation Drainage)
UFGS — Subdrainage Piping	Subdrainage Piping (Unified Facilities Guide Specification)

3 Submittals

3.1 Action Submittals

3.1.1 The Contractor shall submit the following action submittals for the Engineer's review and approval before ordering or installing materials:

Product data for perforated drainage pipe, fittings, couplings, and outlet sections, identifying material, diameter, perforation class, and pipe stiffness.
Product data and certified test reports for geotextile filter fabric, including apparent opening size (ASTM D4751) and permittivity (ASTM D4491).
Product data for geocomposite drainage panels, including core type, compressive strength, in-plane flow capacity, and bonded fabric properties.
Gradation test reports for drainage aggregate, including particle-size distribution and wash-loss percentage (AASHTO T-11).
Shop drawings showing pipe layout, invert elevations, slopes, cleanout and observation-port locations, and outlet details, coordinated with the civil drawings.
A statement from the manufacturer confirming chemical compatibility of pipe material with the soil conditions identified in the geotechnical report.

Action submittals requiredcheckbox

☑ Pipe, fittings, and outlet product data

☑ Geotextile fabric data with AOS and permittivity test reports

☐ Geocomposite drainage panel data

☑ Aggregate gradation and wash-loss reports

☑ Shop drawings with inverts, slopes, cleanouts, and outlets

☐ Pipe-soil chemical compatibility statement

3.2 Informational Submittals

3.2.1 The Contractor shall submit the following informational submittals:

Qualification data for the installing firm demonstrating experience with subdrainage systems of comparable scope.
The manufacturer's installation instructions for pipe, geotextile, and geocomposite drainage panels.
A field quality-control plan describing line-and-grade verification, flush testing, and outlet protection.

Informational submittals requiredcheckbox

☑ Installer qualification data

☑ Manufacturer installation instructions

☑ Field quality-control plan

3.3 Closeout Submittals

3.3.1 The Contractor shall submit the following closeout submittals before final acceptance:

Record drawings showing as-built pipe alignment, invert elevations, cleanout locations, and outlet locations.
Flush-test and, where required, CCTV inspection records confirming line, grade, and free flow to the outlet.
A maintenance instruction describing cleanout access, flushing procedure, and recommended inspection interval.

Closeout submittals requiredcheckbox

☑ As-built record drawings with inverts and outlet locations

☑ Flush-test and CCTV inspection records

☑ Maintenance instructions

4 Quality Assurance

4.1 The installing firm shall have completed subdrainage installations of comparable type and scope, and shall provide qualification data on request.

4.2 Drainage pipe, geotextile, and geocomposite materials furnished under this standard shall each be the product of a single manufacturer for each material type.

4.3 The Contractor shall verify trench bottom line and grade with a laser or string line before placing the aggregate envelope or pipe.

4.4 The Contractor shall not proceed with backfill over installed pipe until line, grade, and outlet connection have been inspected and accepted.

4.5 Pre-Installation Conference

4.5.1 A pre-installation conference shall be held before subdrainage work begins, attended by the Contractor, the installing firm, the earthwork subcontractor, and the Engineer of Record or designated representative.

4.5.2 The pre-installation conference shall review the geotechnical report's groundwater findings, the design slopes and outlet elevations, the filter-fabric and aggregate selections, and the sequencing of subdrainage relative to earthwork and paving operations.

4.5.3 The conference shall confirm the protection and inspection plan for outlets that will be exposed to subsequent base-course and paving operations.

5 Environmental and Service Conditions

NOTE Subdrainage systems operate buried, saturated, and unattended for the life of the structure, so material durability and clog resistance — not initial flow capacity alone — govern the selection. (5.1)

5.2 Pipe Material Selection

5.2.1 The selected pipe material shall be chemically compatible with the soil and groundwater conditions identified in the geotechnical report.

NOTE Corrugated HDPE pipe is the default selection for most subdrainage applications because of its low cost, light weight, and corrosion resistance in typical soils. (5.2.2)

5.2.3 In soils with elevated sulfates, hydrocarbons, or organic content that can degrade polyethylene, solid-wall PVC pipe shall be specified in lieu of HDPE.

5.2.4 Where higher crush resistance is required under deep fill or wheel loading, solid-wall PVC pipe (ASTM D3034, SDR 35) shall be specified.

Subdrainage pipe materialradio

● Corrugated HDPE (ASTM F405 / AASHTO M252)

○ Corrugated HDPE, large diameter (ASTM F667 / AASHTO M294)

○ Solid-wall PVC (ASTM D3034, SDR 35)

5.3 Iron Ochre and Biofouling

NOTE In soils with elevated soluble iron, iron bacteria produce iron ochre — a gelatinous deposit that clogs pipe perforations and geotextile fabric, often within two to five years of installation. (5.3.1)

5.3.2 Where the geotechnical report indicates a risk of iron ochre or biofouling, the system shall be designed with cleanout access at maximum 50 ft spacing to permit periodic flush cleaning.

5.3.3 Where iron ochre risk is present, the maintenance instruction shall describe a flush-cleaning protocol and a recommended inspection interval.

Iron ochre / biofouling risk per geotechnical reportradio

● Low — standard cleanout spacing

○ Elevated — 50 ft cleanout spacing and flush protocol

6 Pipe and Perforation

NOTE The system conveys collected water in a perforated pipe set within a graded aggregate envelope; the perforation pattern and pipe stiffness are selected for the soil and loading condition. (6.1)

6.2 Pipe Diameter

6.2.1 Pipe diameter shall be sized by the Engineer of Record at the design flow using Manning's equation, not selected by convention alone.

NOTE A 4 in. lateral is the standard selection for underslab and pavement edge drains serving tributary areas up to approximately 5,000 to 10,000 sf per run. (6.2.2)

NOTE A 6 in. collector main is the standard selection where multiple laterals combine or the tributary area exceeds the capacity of a 4 in. lateral. (6.2.3)

6.2.4 An 8 in. or larger outlet main shall be provided where the combined tributary area and design flow exceed the capacity of a 6 in. pipe.

Pipe diameterselect

4 in. (laterals, edge drains)

6 in. (collector mains)

8 in. (outlet mains)

10 in. (large outlet mains)

6.3 Perforation Pattern

NOTE Class 1 perforation — two rows of holes at the bottom of the pipe — drains slowly and is selected where the pipe sits in low-permeability soils and water enters primarily from below. (6.3.1)

NOTE Class 2 perforation — holes around the full circumference — is selected where the pipe sits within a free-draining aggregate envelope and water enters from all directions. (6.3.2)

NOTE Slotted-profile pipe is an alternative to circular perforations where flow capacity and ease of CCTV inspection are prioritized over full-perimeter infiltration. (6.3.3)

6.3.4 The perforation pattern shall match the soil and aggregate-envelope condition identified in the design.

Perforation patternradio

● Class 2, fully perforated (aggregate envelope)

○ Class 1, two rows at invert (low-permeability soil)

○ Slotted profile (high flow / CCTV inspection)

6.4 Pipe Stiffness

NOTE Pipe stiffness establishes the pipe's resistance to ring deflection under earth and live loads, measured by the parallel-plate test (ASTM D2412). (6.4.1)

6.4.2 Corrugated HDPE pipe shall have a minimum pipe stiffness of 46 psi.

6.4.3 Solid-wall PVC pipe (SDR 35) shall have a minimum pipe stiffness of 46 psi.

6.4.4 Where H-20 wheel loads apply, the cover over the pipe shall comply with the manufacturer's fill-height tables for the selected pipe and stiffness.

Minimum pipe stiffness (ASTM D2412)range

psi

46115

7 Drainage Aggregate

NOTE The aggregate envelope is the working drain — it conducts water to the pipe and, with the filter fabric, keeps native fines out; an unspecified or dirty aggregate is a leading cause of premature clogging. (7.1)

7.2 Aggregate Gradation

7.2.1 Drainage aggregate shall be clean, washed, durable crushed stone or gravel conforming to a defined gradation; "clean gravel" without a gradation reference is not acceptable.

7.2.2 Drainage aggregate shall conform to ASTM C33 No. 57 gradation (3/4 in. to No. 4) unless the design specifies an alternative gradation.

7.2.3 The aggregate shall have a wash loss not exceeding 0.5% when tested in accordance with AASHTO T-11.

7.2.4 Aggregate gradation shall be selected together with the filter-fabric apparent opening size so that the fabric retains the native soil while the aggregate conducts water freely.

Drainage aggregate gradationselect

ASTM C33 No. 57 (3/4 in. to No. 4)

ASTM C33 No. 67 (3/4 in. to No. 8)

ASTM C33 No. 8 (3/8 in. to No. 16)

Maximum aggregate wash loss (AASHTO T-11)range

%

0.52

Default: 1 %

7.3 Aggregate Envelope Geometry

7.3.1 The aggregate envelope shall extend a minimum of 6 in. below the pipe invert.

7.3.2 The aggregate envelope shall extend a minimum of 6 in. above the pipe crown.

7.3.3 The aggregate envelope shall extend a minimum of 6 in. on each side of the pipe.

NOTE For a 4 in. lateral, the resulting trench width is typically 18 to 24 in.; the trench width for larger pipe increases proportionally. (7.3.4)

7.3.5 Where traffic loading applies above the drain, a minimum of 12 in. of compacted granular structural fill shall be placed above the top of the aggregate envelope before placing subbase or base course.

Aggregate envelope cover below invertrange

in

612

Aggregate envelope cover above crownrange

in

612

8 Filter Fabric

8.1 The geotextile filter fabric is the boundary between native soil and the drainage envelope; it must pass water freely while retaining soil particles, or the system either clogs or fills with migrating fines.

8.2 Fabric Type

NOTE A nonwoven needle-punched geotextile is the default filter fabric for full-trench wrap and for envelope-style drains. (8.2.1)

NOTE A circular-knit pipe sock conforming to ASTM D6707 is an alternative used where a factory sock around the pipe replaces or supplements a full-trench wrap. (8.2.2)

8.2.3 A woven geotextile shall not be used as a subdrainage filter fabric, because its open structure passes fines and clogs the aggregate.

Filter fabric typeradio

● Nonwoven needle-punched geotextile (full-trench wrap)

○ Circular-knit pipe sock (ASTM D6707)

○ Nonwoven wrap with supplemental pipe sock

8.3 Apparent Opening Size

NOTE Apparent opening size (AOS, ASTM D4751) shall be selected so that the AOS is no larger than the D85 grain size of the native soil, preventing soil piping into the drainage aggregate. (8.3.1)

8.3.2 The Engineer of Record shall specify the filter-fabric AOS based on the native soil D85 reported in the geotechnical investigation.

8.3.3 For fine sandy native soils (D85 of 0.10 to 0.20 mm), the AOS shall be in the range of No. 100 to No. 70 sieve (0.15 to 0.21 mm).

8.3.4 For silty native soils, the AOS shall be tightened below the fine-sand value to retain the finer particles.

Filter fabric apparent opening size (ASTM D4751)select

No. 70 (0.21 mm)

No. 80 (0.18 mm)

No. 100 (0.15 mm)

No. 120 (0.125 mm)

8.4 Permittivity

NOTE Permittivity (ASTM D4491) measures the fabric's rate of flow normal to its plane; too low a value chokes the drain even when the openings are correctly sized. (8.4.1)

8.4.2 Filter fabric shall have a minimum permittivity of 0.5 sec⁻¹.

Minimum filter fabric permittivity (ASTM D4491)range

sec⁻¹

0.52

9 Geocomposite Drainage Panels

NOTE A geocomposite drainage panel — a dimpled or cuspated core with a factory-bonded filter fabric — replaces the field-placed aggregate envelope where trench width is constrained or installation speed is critical, and is common in underslab retrofit and against retaining walls. (9.1)

9.2 Where specified, geocomposite drainage panels shall consist of a molded drainage core with a nonwoven geotextile filter fabric bonded to the soil-side face.

9.3 The drainage core shall have a compressive strength adequate for the imposed earth and live loads without collapse of the flow channels.

NOTE The geocomposite drainage core shall discharge into the aggregate envelope or collector pipe at its base, and shall not be terminated against the trench wall. (9.4)

9.5 The transition detail between a geocomposite wall panel and a pipe-in-aggregate collector trench shall be shown on the drawings to avoid field improvisation.

9.6 A geocomposite drainage system shall be installed in accordance with the panel manufacturer's written instructions, including lap, fastening, and termination details.

Drainage methodradio

● Aggregate envelope with perforated pipe (traditional)

○ Geocomposite drainage panel with collector pipe (constrained / retrofit)

10 Cleanouts and Observation Ports

NOTE Cleanouts are the only means of verifying that a buried drain functions and of flushing it when it clogs; an underslab system without cleanouts is essentially non-maintainable. (10.1)

10.2 Cleanouts shall be provided at a maximum spacing of 100 ft on straight runs.

10.3 A cleanout shall be provided at every change in direction greater than 45 degrees.

10.4 A cleanout shall be provided at every grade reversal and at low points in the system.

10.5 In areas subject to iron ochre or biofouling, cleanout spacing shall not exceed 50 ft.

10.6 Cleanout riser pipe shall extend to finished grade.

10.7 In paved or trafficked areas, cleanout risers shall terminate in a traffic-rated frame and cover.

10.8 Observation ports shall be provided where the design requires post-construction verification of the water level or flow within the drain.

Maximum cleanout spacing on straight runsrange

ft

50100

Cleanout cover rating in paved areasradio

● Traffic-rated (H-20) frame and cover

○ Pedestrian-rated frame and cover

○ Landscape-grade access box

11 Outlets

NOTE The outlet is where the system fails most often — a submerged, crimped, or buried outlet stops the entire drain from working regardless of how well the pipe and envelope were installed. (11.1)

11.2 Outlet Elevation

11.2.1 The outlet invert shall be set above the 10-year high-water elevation of the receiving channel or storm structure.

11.2.2 The outlet shall daylight above the normal water surface of the receiving channel; a submerged outlet creates backpressure and can reverse-flow silt into the aggregate envelope.

11.2.3 Where site topography does not permit a gravity daylight outlet above the receiving water surface, the system shall discharge to a sump pit with a pump sized for the design flow.

Outlet typeradio

● Gravity daylight discharge

○ Connection to storm sewer manhole or structure

○ Sump pit with pump

11.3 Outlet Protection

11.3.1 A daylight outlet shall terminate with a flared end section or headwall.

11.3.2 A daylight outlet shall be fitted with a rodent screen of 1/2 in. galvanized hardware cloth.

NOTE Pavement edge-drain outlets are routinely buried or crimped during base-course and paving operations; outlet locations shall be marked and protected, and shall be inspected before final paving. (11.3.3)

11.3.4 The Contractor shall provide as-built outlet locations in the record drawings.

Outlet protection (daylight discharge)checkbox

☑ Flared end section or headwall

☑ 1/2 in. galvanized hardware cloth rodent screen

☐ Riprap or splash apron at discharge

12 Installation

NOTE Subdrainage installation depends on three field controls — true grade, a clean aggregate envelope, and a protected outlet; failures in any one of them defeat the design. (12.1)

12.2 Trench and Bedding

12.2.1 Thermoplastic subdrainage pipe shall be installed in accordance with ASTM D2321.

12.2.2 The pipe shall be bedded on Class IB embedment (crushed stone, gravel, or coarse sand) as the default selection for PE and PVC subdrainage.

12.2.3 Class II embedment may be used where clean angular Class IB stone is unavailable and the pipe stiffness is adequate for the loading.

12.2.4 The trench bottom shall be graded and verified with a laser or string line before placing bedding or pipe.

ASTM D2321 embedment classradio

● Class IB (crushed stone, gravel, coarse sand)

○ Class II (clean coarse-grained soils)

12.3 Slope

NOTE Insufficient or reversed slope is a primary field failure — a low point with reverse grade holds standing water, deposits sediment, and clogs progressively. (12.3.1)

12.3.2 Perforated laterals in free-draining aggregate shall be installed at a minimum slope of 0.5% (1:200).

12.3.3 The design target slope for reliable self-cleaning velocity shall be 1.0% (1:100) where site grades permit.

12.3.4 Where site grades force a slope below 0.5%, an absolute minimum of 0.1% may be used only with the Engineer of Record's documented approval and with cleanouts at both ends of the run.

Pipe sloperange

%

0.12

12.4 Geotextile Placement

12.4.1 Where a full-trench wrap is specified, the geotextile shall line the trench before placing aggregate.

12.4.2 The geotextile shall be lapped over the top of the aggregate envelope after the aggregate is placed.

12.4.3 Geotextile shall be overlapped a minimum of 12 in. at all joints, with the upstream sheet over the downstream sheet.

12.4.4 The geotextile shall be placed without tears, punctures, or folds that would create a fines-migration path or a flow restriction.

Geotextile configurationradio

● Full-trench wrap with aggregate envelope

○ Pipe sock only, in aggregate

○ Full-trench wrap plus pipe sock

12.5 Backfill and Compaction

12.5.1 Heavy compaction equipment operating within the aggregate envelope zone can crush corrugated HDPE laterals; compaction near the pipe shall be controlled accordingly.

12.5.2 Within 2 ft of the pipe, compaction shall be performed only by hand tamping or a light plate compactor.

12.5.3 Backfill above the aggregate envelope shall be placed and compacted in lifts compatible with the pavement or landscape structure above.

12.5.4 A minimum of 12 in. of drainage aggregate cover shall be placed above the pipe before the geotextile cap and backfill are placed.

Backfill above aggregate enveloperadio

● Compacted granular structural fill

○ Approved native material

13 Testing

NOTE Field testing confirms that the installed drain matches the design line and grade and flows freely to the outlet before it is buried and made inaccessible. (13.1)

13.2 After installation, the system shall be visually inspected for line and grade before backfill.

13.3 PVC pipe shall be tested for ring deflection by mandrel, and shall not exceed 5% deflection.

13.4 The system shall be flush-tested from the upstream cleanout to confirm free flow to the outlet.

13.5 Collector mains longer than 100 ft, or any run where the Engineer of Record requires post-backfill verification, shall be inspected by CCTV.

Required field testscheckbox

☑ Visual line-and-grade inspection before backfill

☐ Mandrel deflection test (PVC, 5% max)

☑ Flush test to outlet

☐ CCTV inspection of collector mains

Maximum PVC pipe deflection (mandrel)range

%

57.5

14 Delivery, Storage, and Handling

14.1 Pipe, fittings, geotextile, and geocomposite panels shall be delivered in the manufacturer's original packaging with identifying labels intact.

14.2 Geotextile fabric and geocomposite panels shall be protected from prolonged ultraviolet exposure during storage in accordance with the manufacturer's instructions.

14.3 Pipe and fittings shall be stored on level ground, supported to prevent deformation, and protected from puncture and impact damage.

14.4 Drainage aggregate shall be stored and handled so as to prevent contamination with soil fines that would defeat its wash-loss compliance.

15 Warranty

15.1 The Contractor shall warrant the subdrainage installation against defects in materials and workmanship for the period required by the Contract Documents, but not less than one year from Substantial Completion.

15.2 The warranty shall cover correction of installed pipe with reverse grade, blocked or crushed outlets, and fabric or aggregate placement defects discovered within the warranty period.

Workmanship warranty periodselect

1 year

2 years

5 years

16 Maintenance

NOTE A buried subdrainage system requires periodic flushing and inspection to remain serviceable; the absence of a maintenance plan is what allows iron ochre and sediment to clog a system that was correctly installed. (16.1)

16.2 The maintenance instruction shall describe the cleanout access points, the flush-cleaning procedure, and the recommended inspection interval.

16.3 In systems subject to iron ochre or biofouling, the inspection and flush interval shall be set conservatively to clear deposits before they consolidate.

Recommended inspection / flush intervalselect

Annual

Every 2 years

Every 5 years