Geosynthetics

Start here: ten words every newcomer needs

Overheard on the job

Real-sounding lines from the floor, translated into plain English.

• Waves are knee high by two, stop the cover crew and backfill the anchor trench at first light.

  TranslationThe geomembrane has expanded into tall wrinkles in the afternoon heat, so stop placing soil on it and finish anchoring the liner early tomorrow while it is cool and flat.

• Trial weld peeled on the outside track, bump the wedge and run another before anybody seams production.

  TranslationThe test seam failed the peel test on one of its two welds, so raise the welder's wedge setting and repeat the trial before welding real seams.

• Destruct at station 450 failed non-FTB, so pull bounding samples ten feet each way and cap the stretch in between.

  TranslationA destructive seam sample broke through the weld instead of the sheet, so cut more samples on both sides to find where the bad seam ends and cover that length with a strip patch.

• Slit film will blind off against that silt, put the monofilament woven under the riprap instead.

  TranslationA tape woven geotextile will seal over with fine soil and stop water, so use a woven with round strands and open pores as the filter under the rock armor.

• MARV on grab is 200 and the conformance sample broke at 180, so lot 4 stays on hold.

  TranslationThe lab test on a delivered roll came in below the minimum average roll value for grab tensile strength, so that production lot cannot be installed yet.

• Subgrade is pumping, so it's biax on fabric with a two-foot overlap and a thick first lift, no undercut.

  TranslationSoft ground is squeezing mud into the stone, so lay a biaxial geogrid over a separation geotextile with wide laps and a thick first layer of fill instead of digging out the soft soil.

• Box every patch, spark the boot and tell CQA the air channel on seam 12 held.

  TranslationVacuum-test all patches, spark-test the pipe penetration and report that the pressure test on the dual-track seam passed.

Geotextiles, geogrids, geomembranes, GCLs, geonets and the field names for them.

• Aperturealso opening, grid opening
  Open space between the ribs of a geogrid or between the strands of a woven geotextile.
• Biaxial geogridalso biax, BX grid
  Geogrid with similar strength in both directions, used mainly to stabilize aggregate bases over soft ground.
• Fabricalso filter fabric, road fabric
  Contractor and installer word for any geotextile, as in road fabric, filter fabric or putting the fabric down. Shop talk
• GCLalso geosynthetic clay liner, bentonite mat
  Geosynthetic clay liner: a factory-made barrier of sodium bentonite held between two geotextiles.
• Geocellalso cellular confinement, honeycomb
  Three-dimensional honeycomb of welded polymer strips that is stretched open on site and filled with soil, stone or concrete.
• Geocompositealso drainage composite, drainage geocomposite
  Product that combines two or more geosynthetics, most often a geonet core with geotextile bonded on one or both sides.
• Geogridalso grid, geogrids
  Polymer grid with large open apertures that interlocks with soil or aggregate to reinforce or stabilize it.
• Geomembranealso liner, membrane
  Low-permeability polymer sheet used as a liquid or gas barrier in liners, covers, ponds and tunnels.
• Geonetalso drainage net, biplanar geonet
  Net of extruded polyethylene ribs that forms a thin, high-flow drainage layer within its own plane.
• Geosyntheticalso geosynthetics, geos
  Polymer sheet, grid, net or cell product built into soil or rock to separate, filter, drain, reinforce or contain it.
• Geotextilealso fabric, filter fabric
  Permeable fabric used with soil to separate, filter, drain, reinforce or protect, made woven, nonwoven or knitted.
• HDPEalso high-density polyethylene, HDPE liner
  High-density polyethylene: the stiff, chemically resistant polymer used for most landfill and mining geomembranes.
• Lineralso poly, the sheet
  Everyday site name for a geomembrane, or for the whole barrier system it belongs to. Shop talk
• LLDPEalso linear low-density polyethylene, LL
  Linear low-density polyethylene: a softer, more flexible geomembrane polymer that follows uneven ground better than HDPE.
• Milalso mils, thou
  One thousandth of an inch, the unit North American crews use for geomembrane thickness.
• Monofilament wovenalso woven monofilament, mono
  Woven geotextile of round single-strand yarns that leaves regular open pores for high flow and good filtration.
• Nonwoven geotextilealso needlepunched geotextile, nonwoven fabric
  Geotextile made by needlepunching or heat-bonding fibers into a felt-like sheet, used for filtration, drainage and cushioning.
• PVCalso polyvinyl chloride, vinyl liner
  Polyvinyl chloride: a flexible, plasticized geomembrane that folds and seams easily, used in ponds, canals and water features.
• Silt fencealso sediment fence, filter fence
  Temporary geotextile fence along a slope or site edge that slows runoff and traps its sediment.
• Slit filmalso slit-film woven, woven slit film
  Woven geotextile made from flat polypropylene tapes cut from extruded film, strong and cheap but a poor filter.
• Textured geomembranealso textured liner, textured sheet
  Geomembrane with a roughened surface that raises friction against soil and other geosynthetics on slopes.
• Triaxial geogridalso triax, TX grid
  Geogrid with triangular apertures that gives fairly even stiffness in every direction across its plane.
• Uniaxial geogridalso uni, uniaxial grid
  Geogrid with its strength concentrated in one direction, used to reinforce walls and steep slopes.
• Wick drainalso PVD, prefabricated vertical drain
  Field name for a prefabricated vertical drain: a plastic core in a filter jacket pushed into soft clay to speed settlement. Shop talk

The jobs geosynthetics do and the strengths, factors and specs used to design them.

• AASHTO M 288also M 288, M288
  US highway specification for geotextiles that sets required properties by application and survivability class.
• Drainagealso in-plane drainage, drainage function
  Carrying water along the plane of a geosynthetic to an outlet, as in wall backdrains and leak detection layers.
• Filtrationalso filter, filter function
  Letting water pass across a geotextile while holding back the soil particles it carries.
• Interface frictionalso interface shear strength, interface friction angle
  Shear resistance between a geosynthetic and soil, or between two geosynthetics, that keeps lined slopes from sliding.
• LTDSalso long-term design strength, Tal
  Long-term design strength: reinforcement strength left after reductions for creep, installation damage and aging.
• MARValso minimum average roll value
  Minimum average roll value: the lowest average test result a product guarantees for any roll it ships.
• Reduction factoralso RF, partial factor
  Number that divides a geosynthetic's index strength to allow for creep, installation damage or degradation in service.
• Reinforcementalso soil reinforcement, reinforcing function
  Using the tensile strength of a geosynthetic to hold soil together so it can stand steeper or carry more load.
• Separationalso separator, separation function
  Keeping two different soil layers, such as an aggregate base and a soft subgrade, from mixing under load.
• Stabilizationalso subgrade stabilization, base stabilization
  Improving how soft ground or an aggregate base carries traffic by adding geogrids or geotextiles.
• Survivabilityalso construction survivability, installation survivability
  A geosynthetic's ability to make it through shipping, placement and compaction without being damaged.

Opening size, flow across and along fabrics, and how filters clog or let soil escape.

• AOSalso apparent opening size, O95
  Apparent opening size: an index of the largest openings in a geotextile, given as a US sieve number or in millimeters.
• Blindingalso surface blinding
  Sealing of a geotextile surface by a thin layer of fine particles that blocks flow across it.
• Cloggingalso clog
  Gradual loss of flow through a geotextile as soil particles or deposits lodge inside its pores.
• Gradient ratioalso GR, gradient ratio test
  Laboratory ratio that shows whether a soil and geotextile pair is starting to clog under steady seepage.
• Permittivityalso cross-plane flow
  Rate of water flow across a geotextile per unit head, the basic measure of its cross-plane flow capacity.
• Pipingalso soil piping, internal erosion
  Soil particles washing through a filter or out of an embankment, leaving voids and channels behind.
• Transmissivityalso in-plane flow, hydraulic transmissivity
  In-plane flow capacity of a geosynthetic drainage layer per unit width, under a given gradient and normal load.

Index tests, creep, damage, aging and the lab checks run on every lot.

• Asperity heightalso texture height, asperity
  Height of the raised texture on a textured geomembrane, measured from the core of the sheet.
• Carbon blackalso CB, carbon black content
  Fine black pigment blended into polyethylene geosynthetics, usually at 2 to 3 percent, to block ultraviolet damage.
• CBR puncturealso static puncture, CBR puncture strength
  Puncture test in which a 50 mm plunger is pushed through a clamped geosynthetic, simulating a stone pressing into it.
• Creepalso creep strain
  Slow, continuing stretch of a geosynthetic under a constant load over time.
• Grab tensilealso grab strength, grab
  Index tensile test on geotextiles in which a 100 mm wide specimen is gripped by 25 mm jaws in its middle.
• Installation damagealso construction damage, ID
  Loss of geosynthetic strength caused by placing, spreading and compacting fill on it.
• Mass per unit areaalso weight, basis weight
  Weight of a geosynthetic per square meter or square yard, the basic identity check for geotextiles.
• OITalso oxidative induction time, Std-OIT
  Oxidative induction time: a measure of how much antioxidant protection remains in a polyolefin geosynthetic.
• Stress crackingalso environmental stress cracking, ESC
  Brittle cracking of polyethylene geomembranes under long-term tension well below their yield strength.
• Swell indexalso free swell, swell index test
  Test of how much a sample of bentonite from a GCL swells in water, an indicator of its sealing quality.
• Trapezoid tearalso trap tear, trapezoidal tear
  Test of the force needed to keep a tear running across a geotextile from a pre-cut slit.
• UV resistancealso UV stability, ultraviolet resistance
  How much strength a geosynthetic keeps after exposure to ultraviolet light in an accelerated weathering test.
• Wide-width tensilealso wide width tensile strength, wide strip tensile
  Tensile test across a 200 mm wide specimen that gives strength per unit width for reinforcement design.

Walls, slopes, roads, liners and caps, and the dirt-work slang that goes with them.

• Anchor trenchalso anchorage trench, key trench
  Trench along the top of a slope where the edge of a geosynthetic is buried to hold it in place.
• Bathtubbingalso bathtub effect, bathtub
  Water or leachate collecting inside a lined area because more gets in from above than can drain out below. Shop talk
• Burritoalso burrito wrap, fabric-wrapped drain
  Site slang for a trench drain of stone completely wrapped in geotextile, often around a perforated pipe. Shop talk
• Capalso final cover, cover system
  Final cover system placed over a closed landfill or waste area to keep water out and control gas.
• Composite lineralso composite barrier, composite lining system
  Barrier made of a geomembrane in direct contact with a low-permeability soil or GCL layer beneath it.
• Daylightalso daylighted, daylighting
  To bring a drain or drainage layer out to open ground lower down so its water can escape by gravity. Shop talk
• Leak detection layeralso LDS, leak detection system
  Drainage layer between the primary and secondary liners of a double liner that collects and reveals leakage.
• Liftalso layer, fill lift
  One layer of fill placed and compacted at a time, the unit by which walls, slopes and embankments are built.
• MSE wallalso MSE, reinforced soil wall
  Mechanically stabilized earth wall: compacted fill reinforced with layers of geogrid or steel strips behind a facing.
• Mud wavealso mudwave, mud bulge
  Bulge of very soft soil shoved up ahead of fill being placed on weak ground. Shop talk
• Overlapalso lap, laps
  Width by which neighboring rolls of geotextile, geogrid or GCL lie over one another to keep a continuous layer.
• Pumpingalso subgrade pumping, fines migration
  Fines from a wet subgrade being forced up into the aggregate base by repeated traffic loads.
• RSSalso reinforced soil slope, reinforced steepened slope
  Reinforced soil slope: an embankment built steeper than its fill could stand alone by layering geogrid or geotextile in it.
• Runoutalso runout length, crest runout
  Flat length of geosynthetic between the crest of a slope and the anchor trench.
• Shinglealso shingling, shingled lap
  To lay overlapping panels with the upslope piece on top, so water sheds over the lap instead of into it. Shop talk
• Sockalso filter sock, pipe sock
  Knitted or nonwoven geotextile sleeve slipped over perforated drainpipe to keep soil out of the slots. Shop talk
• Subgradealso foundation soil, native soil
  Native or prepared soil surface on which a pavement, aggregate base or liner system is built.
• Undercutalso undercut and replace, over-excavation
  Digging out soft or unsuitable subgrade below grade and replacing it with better fill. Shop talk
• Wrap-around facingalso wrapped face, wrap face
  Wall or slope face formed by folding each geotextile or geogrid layer up the face and back into the fill above.

Deploying panels, welding geomembrane and the defects crews fight in the field.

• Bootalso pipe boot, penetration boot
  Field-built geomembrane sleeve that seals a liner around a pipe or other penetration. Shop talk
• Burn-throughalso burn, burnout
  Hole or severe thinning in a geomembrane where a welder ran too hot or stopped on the sheet. Shop talk
• Deploymentalso placement, unrolling
  Unrolling and positioning geosynthetic rolls in their final location before seaming or covering.
• Extrusion weldalso extrusion seam, extrudate weld
  Geomembrane seam made by laying a bead of molten polymer along the edge of an overlap, used for patches and details.
• Fishmouthalso fish mouth, fish-mouth
  Wrinkle or bulge in the top sheet of a seam overlap that stops the two sheets lying flat for welding. Shop talk
• Fusion weldalso hot wedge weld, wedge weld
  Geomembrane seam made by melting the facing surfaces of two overlapped sheets and pressing them together.
• Grindingalso grind, seam preparation
  Lightly abrading geomembrane before an extrusion weld to remove the oxidized surface and dirt.
• Gunalso extruder, extrusion gun
  Installer slang for the hand-held extrusion welder used on patches, boots and detail welds. Shop talk
• Panelalso sheet, liner panel
  One continuous piece of geomembrane as deployed, numbered and tracked through seaming and testing.
• Patchalso repair
  Piece of geomembrane extrusion-welded over a hole, defect, destructive sample cut-out or failed seam section.
• Sandbagsalso ballast, bags
  Bags of sand laid on deployed geomembrane and other geosynthetics to hold them down against wind. Shop talk
• Seameralso welder, welding tech
  Welding technician who makes and repairs geomembrane seams on a liner crew. Shop talk
• Squeeze-outalso flash, bead squeeze-out
  Bead of molten polymer pressed out along the edge of a fusion seam by the welder's rollers. Shop talk
• Tackalso tacking, tack weld
  To spot-weld overlapped geomembrane with a hot-air tool so it stays aligned before the final extrusion weld. Shop talk
• Tie-inalso tie in, liner tie-in
  Connection that joins a new liner to an existing one, as when a landfill cell is expanded. Shop talk
• Trampoliningalso bridging, bridged liner
  Geomembrane pulled tight across a corner or the toe of a slope, leaving a gap underneath like a trampoline. Shop talk
• Trial weldalso test weld, trial seam
  Short test seam made on scrap geomembrane before production welding to prove the machine settings and the operator.
• Wavesalso wrinkles, thermal wrinkles
  Installer word for the wrinkles that form in a geomembrane as it expands in the sun. Shop talk
• Wedgealso wedge welder, hot wedge
  Installer shorthand for the hot wedge welder, or for the heated wedge inside it. Shop talk

Nondestructive and destructive seam tests and the quality assurance record.

• Air channel testalso air pressure test, air test
  Pressure test of a dual-track fusion seam in which the gap between the two welds is pumped up and watched for loss.
• Air lancealso air lance test, air lancing
  Nozzle that blows compressed air at the edge of a lapped seam to find unbonded spots in thin, flexible liners.
• Conformance testingalso conformance sampling, acceptance testing
  Testing samples from rolls delivered to a site to confirm the material matches the specification.
• Couponalso specimen, seam coupon
  Narrow strip cut across a seam sample for peel or shear testing, usually one inch wide. Shop talk
• CQAalso construction quality assurance, QA
  Construction quality assurance: independent monitoring and testing that a geosynthetic system was built as designed.
• Destructalso destruct sample, DS
  Installer shorthand for a destructive seam sample, and for the job of cutting one out. Shop talk
• Destructive testalso destructive seam test, DT
  Testing seam samples cut from installed geomembrane in peel and shear to prove seam strength.
• Dogbonealso dumbbell, dog bone
  Dumbbell-shaped specimen punched from geomembrane sheet for tensile and stress crack tests. Shop talk
• ELLalso electrical leak location, leak location survey
  Electrical leak location: surveys that find holes in an installed geomembrane by tracing current through them.
• FTBalso film tear bond
  Film tear bond: a seam coupon that breaks in the sheet beside the weld rather than through the weld itself.
• Peel testalso peel, peel strength
  Seam test that pulls the top sheet away from the bottom sheet across the weld to check how well they fused.
• Shear testalso shear, bonded seam strength
  Seam test that pulls the two sheets apart in their own plane, loading the whole weld in shear.
• Spark testalso spark testing, holiday test
  Holiday test for extrusion welds in which a high-voltage probe sparks through any gap to a buried conductive wire.
• Tensiometeralso field tensiometer, seam tester
  Portable tensile tester used on site to pull geomembrane seam coupons in peel and shear.
• Vacuum boxalso vacuum box test, box
  Clear-topped box pulled to a vacuum over soapy geomembrane so leaks in seams and patches show up as bubbles.

Frequently asked questions

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