Key Properties for Selecting a Non-Woven Geotextile
When you’re choosing a non-woven geotextile, the key properties you need to evaluate are its mechanical, hydraulic, and endurance characteristics. These aren’t just fancy terms; they directly determine whether the fabric will perform its job—be it separation, filtration, drainage, or protection—without failing over the long term. Getting this selection wrong can lead to costly project delays, structural instability, or even complete system failure. The right combination of properties hinges entirely on the specific application, soil conditions, and environmental stresses the geotextile will face. It’s less about finding a one-size-fits-all product and more about matching the material’s engineered capabilities to the project’s precise demands.
Mechanical Properties: The Fabric’s Strength and Stability
Think of mechanical properties as the geotextile’s skeleton. They define its physical strength and ability to withstand forces during installation and throughout its service life. The three most critical mechanical properties are tensile strength, puncture resistance, and seam strength (for sewn panels).
Tensile Strength measures how much pulling force the fabric can handle before it breaks. It’s crucial for applications like slope reinforcement or where the geotextile might be tensioned. This is tested in both the machine direction (MD – the direction the fabric is manufactured) and cross-machine direction (CMD). For instance, a standard non-woven geotextile used under a roadway might have a tensile strength of 20 kN/m, while a heavy-duty one for a landfill cap might need 80 kN/m or higher. It’s not just about the peak strength, though. The force at which the fabric elongates is also vital; a higher elongation at break can be beneficial for absorbing stresses without tearing.
Puncture and Tear Resistance are your indicators of survivability. Imagine dropping sharp, angular aggregate onto the fabric during installation. Puncture resistance (often measured by CBR Puncture) indicates its ability to resist a concentrated point load. Tear resistance (like Trapezoid Tear) shows how well a small nick or rip will resist propagating into a large tear. A geotextile with high puncture resistance is essential when placing over rocky subgrades or under coarse stone layers.
The table below summarizes typical mechanical property ranges for different project applications:
| Application | Tensile Strength (min. kN/m) | CBR Puncture (min. N) | Typical Weight (g/m²) |
|---|---|---|---|
| Underlayment for Pavement (Low Traffic) | 12 – 20 | 1800 – 2500 | 150 – 200 |
| Railway Bed Stabilization | 25 – 40 | 3000 – 4500 | 250 – 350 |
| Landfill Drainage Layer | 40 – 70 | 5000 – 8000 | 400 – 600 |
| Erosion Control on Slopes | 18 – 30 | 2200 – 3500 | 200 – 300 |
Hydraulic Properties: Managing the Flow of Water
If mechanical properties are the skeleton, hydraulic properties are the geotextile’s circulatory system. They control how water moves through the fabric, which is fundamental to its filtration and drainage functions. The two key parameters here are permeability (or permittivity) and apparent opening size (AOS).
Permittivity (ψ) is a measure of the fabric’s in-plane water flow capacity. It’s essentially the permeability normalized for thickness. A higher permittivity value means water can pass through the fabric more easily, which is critical for drainage applications where the geotextile is intended to transport water within its plane to relieve pore water pressure. For a drainage trench, you might need a permittivity greater than 2.0 sec⁻¹, whereas for simple separation, a value of 0.5 sec⁻¹ could be sufficient.
Apparent Opening Size (AOS), sometimes called the equivalent opening size (EOS), is arguably the most critical filtration property. It indicates the approximate largest opening in the fabric, typically reported in millimeters or U.S. Sieve sizes (e.g., O95 means 95% of the openings are smaller than this size). The golden rule of filtration is that the AOS must be small enough to retain the surrounding soil particles while being large enough to allow water to pass freely. A common design criterion is that the O95 should be less than or equal to the D85 (the sieve size that 85% of the soil particles pass) of the soil being retained. Using a NON-WOVEN GEOTEXTILE with an AOS that’s too small can lead to “blinding,” where fine particles clog the fabric surface, drastically reducing permeability. Conversely, an AOS that’s too large will allow soil to wash through, leading to erosion and loss of structural support.
Endurance and Environmental Properties: Ensuring Long-Term Performance
A geotextile might have fantastic initial properties, but if it degrades quickly, it’s useless. Endurance properties predict how the fabric will perform over decades. This includes UV resistance, chemical resistance, and biological resistance.
UV Resistance is critical if the geotextile will be exposed to sunlight for any significant period (more than a few days to a few weeks) before being covered. Ultraviolet radiation can break down the polymer chains in polypropylene and polyester, causing the fabric to become brittle and lose strength. This is measured by the percentage of tensile strength retained after a specified number of hours in a UV exposure test (e.g., ASTM D4355). If long-term exposure is expected, you must select a geotextile with carbon black or other UV stabilizers compounded into the polymer, not just coated on the surface.
Chemical and Biological Resistance depends heavily on the polymer type. Polypropylene is highly resistant to a wide range of chemicals, including acids and alkalis, making it the go-to choice for landfill liners, acid mine drainage, and agricultural applications. However, it is susceptible to oxidation at high temperatures. Polyester has excellent resistance to creep and is generally stronger, but it can be vulnerable to hydrolysis (chemical breakdown by water) in high-pH environments, like those found in fresh concrete or certain backfills. You must check the pH and chemical composition of the soil and water the geotextile will contact. Biological resistance is generally high for both polymers, as they do not serve as a food source for microorganisms, but the additives used can sometimes affect this.
Selecting by Weight: A Common but Incomplete Metric
Many people start their selection process by looking at the weight of the geotextile, measured in grams per square meter (g/m² or GSM). While weight can be a rough indicator of thickness and robustness, it is a secondary property. You cannot specify a geotextile by weight alone and expect reliable performance. A heavier fabric might be thicker, which can be good for puncture resistance, but it doesn’t automatically guarantee higher tensile strength or the correct AOS for your soil. Two geotextiles can have the same weight but vastly different mechanical properties due to variations in the manufacturing process (e.g., needle-punching density, fiber type). Always base your specification on the tested values for the primary properties discussed above, not just on the mass per unit area.
The Critical Role of Roll Size and Installation Survivability
An often-overlooked but practical aspect is the physical roll dimensions. The width and length of the rolls impact installation speed, the number of seams, and material waste. A wider roll (e.g., 5.2 meters or 6.0 meters) means fewer seams for a large area like a pond liner, which translates to faster installation and reduced potential for seam failure. The roll weight must also be considered for handling on-site with available equipment.
Finally, all the laboratory properties are meaningless if the geotextile gets destroyed during installation. This is where survivability properties come in. These are often assessed by modified versions of tests like abrasion resistance. The real-world installation conditions—the type of subgrade, the placement method for the overlying material (dropped from a height, pushed by a bulldozer)—must be matched with a geotextile robust enough to survive. Most project specifications will include a “Survivability” classification (e.g., Class 1, Class 2) that defines the minimum property requirements based on the severity of the installation conditions.