Technical BulletinH IGH DENSITY POLYETHYLENE PIPE HDPE Pipe Installation PracticeLANE corrugated high density polyethylene Classes IA, IB, and II are preferred over Class III(HDPE) pipe, appropriate backfill material and when available because they are stiffer materials,proper installation practice all work together to limit pipe deflection and permit greater fill heights.result in a dependable drainage installation. HDPE Also, construction may be faster because lesspipe, like all flexible pipes, depends on soil-pipe compactive effort is generally required. Class IIIinteraction to develop its strength. Thus, proper material should not be used where waterinstallation and backfilling are essential to conditions in a trench can cause instability.successful performance. This technical bulletinaddresses typical installations in trench andembankment conditions. Unusual conditions may BACKFILL MATERIAL SIZErequire additional investigations, including the Pipe Diameter (ID) Max. Particle Sizerecommendations of a qualified geotechnical or in. mm in. mmsoils engineer. More detailed information on 6 150 3/8 10installation and backfill may be found in ASTMD2321, " Standard Practice for Underground 8-15 200-375 5/8 15Installation of Thermoplastic Pipe for Sewers and 18-48 450-1200 1 1/2 40Other Gravity-Flow Applications."Installation practices must always comply Cement slurry and controlled low strength materialwith local, state and federal codes and (CLSM) are excellent backfill material provided they yield adequate compressive strength and thesafety regulations. pipe is restrained to avoid flotation during installation.Material for Foundation,Bedding and Backfill Foundation and BeddingThe pipe must be surrounded by compactedmaterial to distribute vertical loads uniformly to A good foundation and bedding are critical to pipethe pipe and to provide passive resistance to pipe performance and service life. They are essential todeflection. Material selection depends on help maintain proper pipe elevation, eliminateavailability and cost. Granular materials with little undesirable stresses in the pipe and ensure goodor no plasticity are preferred. Frozen lumps, hydraulic performance.chunks of clay, organic matter and large rock areunacceptable. Acceptable materials are The foundation material beneath the pipe mustsummarized in Table 1 by their ASTM Class and provide a uniform resistance to the loads on theSoil Group designation. pipe. www.lane-enterprises.com
Sharp longitudinal and lateral variations However, if special equipment is availablein the foundation must be avoided. If to provide a quality installation with arock is encountered, excavate and replace narrow trench, the minimum width can bewith gravel or lightly compacted material. reduced. If material such as CLSM isSuch cushion should have a depth of used that requires no compaction, theapproximately ½ in. per ft. (42 mm/m) of trench width can be as little as the pipethe planned fill depth over the pipe outside diameter, plus 6 in. (150 mm).(6 in.-150 mm minimum, 24 in.-600 mmmaximum). If soft foundation material is The trench must be filled with material,encountered that must be removed to placed and compacted in layers to form amaintain grade, remove the material for a "structural backfill" surrounding the pipe.depth of about 2 ft. (0.6 m) and replace The backfill must be compacted to awith suitable compacted material. The minimum of 90 percent of maximumwidth of this material should be 2.5 diam- density as determined by ASTM D698 oreters on either side of the pipe for pipe 12 AASHTO T99. The envelope shouldin. (300 mm) diameter or less. For larger extend to 12 in. (300 mm) above the toppipe, the width should be established by of the pipe before the remainder of the fillthe engineer. is placed in the trench. The trench wall is assumed to have a stiffness at least that ofThe upper 4 in. (100 mm) of the bedding the compacted backfill. If soft trenchshould be relatively loose material so the walls are encountered, additionalcorrugations can be seated. Frozen excavation may be required.lumps, chunks of clay, organic matter andlarge rock are unacceptable. The pipemay be installed by shaping the beddingsurface to conform to the pipefor a width of about one-halfthe diameter. A second methodis to place the pipe directly onthe bedding, in which caseparticular care must be takento compact the backfill underthe haunches of the pipe toprovide uniform support.TrenchConstructionThe trench should be wideenough for placement andcompaction of backfill, especially the Excavate trenches to ensure the trenchmaterial placed beside the pipe and that in walls are stable under all conditions.the haunch area below the spring line. Slope the walls or provide support inGenerally, the minimum trench width conformance with safety standards. Allshould not be less than the greater of (1) appropriate safety practices andthe pipe outside diameter plus 16 in. (400 regulations must be followed to avoidmm), or (2) the pipe outside diameter trench collapse. If high ground water istimes 1.25, plus 12 in. (300 mm). encountered, dewatering may be required to achieve a safe installation that meets requirements.
Embankment Construction Backfill PlacementIn embankment construction, the compacted In either trench or embankment construction, theenvelope of "structural backfill" must surround the backfill material must be placed in layers andpipe with a width adequate to resist forces caused compacted to a minimum of 90 percent ofby construction equipment. The width of this zone maximum density as determined by ASTM D698on each side of the pipe should be one diameter, or ASSHTO T99. The maximum thickness of thewith a minimum of 12 in. (300 mm) and a layers or lifts should not exceed 6 in. (150 mm).maximum of 24 in. (600 mm). The envelope The lift thickness, placement technique andshould extend to 12 in. (300 mm) above the top of compaction method must be such that compactionthe pipe before normal embankment material is under the haunches is obtained.placed. continued on next page > TABLE 1 Recommended Backfill Materials ASTM ASTM Similar D2321 Type D2487 Description AASHTO Class Soil Group Type Angular, crushed stone or rock, crushed IA Manufactured Aggregates; gravel, broken coral, crushed slag, cinders open-graded, clean. or shells; large void content, contain little or no fines. Manufactured Processed Angular, crushed stone (or other Class 1A IB materials) and stone/sand mixtures with Aggregates; dense-graded, clean. gradations selected to minimize migration of adjacent soils; contain little or no fines. GW Well-graded gravels and gravel/sand A1, II Coarse-Grained Soils; clean. mixtures, little or no fines. A3 GP Poorly graded gravels and gravel/sand mixtures, little or no fines. SW Well-graded sands and gravelly sands, little or no fines. SP Poorly-graded sands and gravelly sands, little or no fines. Coarse-Grained Soils; borderline e.g. Sands which are borderline between clean to with fines. GW clean and with fines. GC SP SM III Coarse-Grained Soils with Fines. GM Silty gravels, gravel-sand-silt mixtures. A2 GC Clayey gravels, gravel-sand-clay mixtures. SM Silty sands, sand-clay mixtures SC Clayey sands, sand/clay mixtures. Note: Compact backfill material to minimum of 90% of maximum density per ASTM D698 or AASHTO T99. Table adapted from ASTM D2321.
Each layer must be compacted before the next lift is placed. Backfillmust proceed evenly on each side of the pipe. Care must be taken toavoid pipe distortion or excessive local or general deflection. Suchunacceptable deformations can result from either excessive or inadequatecompaction or from construction equipment. Do not allow compactionor other equipment to contact and damage the pipe. Compactiontechniques must be compatible with the backfill materials used, and thewidth of the area being compacted.Mechanical compaction is generally used. However, water consolidationmethods can be used on free-draining backfill material if care is taken toprevent flotation. Conditions must be controlled and approved by theengineer.Construction LoadsIt is important to protect the pipe from equipment loads duringconstruction. Heavy equipment must not be allowed close to or overburied pipe unless provisions are made to accommodate the resultantloads. Depending on the size of the equipment and class of fill material,a minimum cover from 2 ft. (0.6 m) to 4 ft. (1.2 m), or more forexceptional loads, may be required. (see table 2) For shallowinstallations, it may be necessary to mound and compact material overthe pipe to provide the minimum cover. The mound can be removed andfinal grade established after construction. TABLE 2 COVER FOR CONSTRUCTION LOADS Minimum Cover, in., for indicated Axle Loads, kips Nominal Pipe Drain with Lane Diameter, ft 18.0-50.0 50.0-75.0 75.0-110.0 110.0-150.0 Lane Enterprises, Inc. 2.0-3.0 24.0 30.0 36.0 36.0 3905 Hartzdale Drive, Suite 514 Camp Hill, PA 17011 3.5-4.0 36.0 36.0 42.0 48.0 717-761-8175 Fax 717-761-5055 4.5-5.0 36.0 36.0 42.0 48.0 New York Minimum cover shall be measured from the top of the pipe to the Ballston Spa 518-885-4385 top of the maintained construction roadway surface. If unpaved, Bath 607-776-3366 the surface shall be maintained. North CarolinaMultiple Pipes Statesville 704-872-2471When two or more pipes are installed in adjacent parallel lines, sufficient Pennsylvaniaspace must be provided between the pipes to provide for adequate Bedford 814-623-1191compaction of the structural backfill. One rule-of-thumb is to use a Carlisle 717-249-8342spacing between pipes equal to 12 in. (300 mm), or one-half the nominal King of Prussia 610-272-4531pipe diameter, whichever is greater. This can be increased if necessary to Pulaski 412-652-7747accommodate compaction. Virginia Bealeton 540-439-3201 The information contained in this technical bulletin is general in nature and is intended for use in conjunction with competent engineering advice as to its suitability for any specific application. Nothing in this bulletin is intended as a Dublin 540-674-4645 representative or warranty that such data is suitable for any particular application or purpose. www.lane-enterprises.com