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Geotextiles do the supporting work in a geosynthetic system: nonwoven fabrics cushion geomembranes and filter soils, while woven fabrics separate and reinforce. Specifications turn on weight class, strength, and hydraulic properties, each defined by a specific ASTM test method.
| Property | Test method | What it tells you |
|---|---|---|
| Mass per unit area (weight class) | ASTM D5261 | The oz/sy rating that drives cushion performance |
| Grab tensile strength | ASTM D4632 | Resistance to installation and service tension |
| CBR puncture resistance | ASTM D6241 | Resistance to stones and angular subgrade |
| Trapezoid tear strength | ASTM D4533 | Resistance to tear propagation from a snag or cut |
| Apparent opening size (AOS) | ASTM D4751 | The soil particle size the fabric retains |
| Permittivity | ASTM D4491 | How freely water passes through the fabric |
| UV resistance | ASTM D4355 | Strength retained after weathering exposure |
| Weight class (oz/sy) | Typical role | Selection notes |
|---|---|---|
| 4 to 6 oz | Separation, filtration, light protection | Fine-grained or well-prepared subgrades; drainage and filter layers |
| 8 oz | General geomembrane cushion | Common baseline for prepared subgrades with limited gravel content |
| 10 to 12 oz | Heavy cushion | Coarser subgrades or cover soils with angular particles; deeper waste or soil loads |
| 16 oz and heavier | Severe puncture protection | Rocky subgrades, drainage stone contact, and high normal loads; confirm with a puncture analysis or GRI GT12 protection evaluation |
Woven and nonwoven geotextiles are both polypropylene or polyester fabrics, but they behave very differently and are specified for different functions. Nonwoven needle-punched geotextiles are made from randomly oriented fibers mechanically entangled into a thick, felt-like sheet. That structure gives them high elongation, excellent water flow through the plane of the fabric, and the ability to absorb and spread point loads. They are the default choice for cushioning geomembranes, filtering soils, and wrapping drainage aggregate.
Woven geotextiles are made from slit-film tapes or monofilament yarns woven into a tight grid. They deliver high tensile strength at low elongation, which suits separation and reinforcement under haul roads, working platforms, and aggregate bases. The tradeoff is hydraulic performance: slit-film wovens pass much less water and can blind off in silty soils. Specify nonwoven where the fabric must protect or filter, and woven where it must carry load or separate soil layers under traffic.
Cushion geotextiles are specified by mass per unit area, measured in ounces per square yard under ASTM D5261. The right weight class depends on what the geomembrane has to survive: the particle size and angularity of the subgrade or drainage layer, the normal load from waste, soil, or water above the liner, and the membrane material itself. A 60 mil HDPE liner over a smooth, rolled subgrade may need only a light fabric or none at all, while the same liner beneath several feet of angular drainage stone typically calls for a 12 to 16 oz nonwoven cushion.
For critical containment work, the selection is not a rule of thumb but a calculation. Designers evaluate liner protection using puncture testing and methods such as the GRI GT12 protocol, which rates a candidate cushion fabric against a specified stone size and normal stress. Project specifications commonly state a minimum weight class plus minimum average roll values (MARV) for grab tensile, CBR puncture, and tear, so that any compliant roll delivered to the site meets the design assumptions.
When a geotextile works as a filter, two hydraulic properties control the design. Apparent opening size, or AOS, measured under ASTM D4751, describes the largest soil particle that will effectively pass through the fabric; it is reported as a sieve size, and the specified value must be small enough to retain the protected soil without clogging. Permittivity, measured under ASTM D4491, describes how freely water flows through the fabric normal to its plane. A good filter balances the two: open enough to relieve water pressure, tight enough to hold soil in place.
These properties matter even on cushion applications. A cushion fabric placed beneath a geomembrane on a wet subgrade should still allow pore water to dissipate rather than trapping it against the liner. AASHTO M288, the standard specification for geotextiles in transportation applications, groups fabrics into survivability classes and pairs each function (separation, filtration, stabilization) with required AOS and permittivity values, and many civil specifications reference it directly.
A cushion geotextile is required whenever the surface in contact with the geomembrane could puncture it under load. Common triggers include gravelly or rocky subgrades that cannot be economically fine-graded, drainage stone or leachate collection aggregate placed directly above a liner, concrete or shotcrete surfaces with protrusions, and any location where equipment or cover soil placement concentrates stress on the membrane. Landfill regulations under RCRA Subtitle D drive many of these details, since composite liner systems must survive decades of waste loading without leakage.
The fabric works by spreading point loads: a stone that would eventually puncture bare geomembrane instead presses into a thick nonwoven that distributes the force over a wider area. Cushion layers are cheap insurance against liner repair or a failed leak test, which is why most engineered containment specifications include one on at least one side of the membrane.
Geotextiles are joined in the field by overlapping, sewing, or heat bonding, and the specification should state which is required. Simple overlaps of 12 to 24 inches are common for separation and cushion duty on stable ground, with wider overlaps on soft subgrades where soils could squeeze between panels. Sewn seams, tested for strength under ASTM D4884, are specified where the fabric carries tension or where overlaps could shift during covering. Heat tacking is often used to hold panels in position on slopes ahead of geomembrane deployment.
Placement quality matters as much as the fabric itself. Panels should lie flat without folds, be anchored against wind, and be covered promptly, since polypropylene loses strength with extended UV exposure; ASTM D4355 defines the retained-strength test specifications cite for allowable exposure. EC Applications deploys and seams geotextiles as part of complete lining systems, checking delivered rolls against the specified MARVs before they go in the ground.
Single and composite-lined cells, caps, and leachate ponds for MSW, hazardous, and coal-ash sites.
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