Permeability may be the most important variable among all performance parameters of geotextiles, and it is a key component for drainage, filtration, and long-term stabilization of soil properties. Without suitable permeability, geotextiles cannot achieve their primary engineering functions.
In civil engineering applications where water flow control is the primary task, the success or failure of a geotextile depends on its permeability. The permeability of a geotextile refers to the ease with which water can pass through it. Typically, permeability is expressed as the ease of water flow through a geotextile under a known pressure, and it applies to both nonwoven and woven geotextiles.
Their permeability values can vary significantly. In general, nonwoven geotextiles have higher permeability. This is because water can pass through the needle-punched structure, while soil particles cannot. However, this special nonwoven process means that its strength is lower than that of some woven geosynthetic materials. Woven geotextiles usually have higher strength, but in some cases their permeability is lower. However, for drainage and filtration applications, an appropriate balance between permeability and filtration performance must be achieved.
Why does permeability control filtration performance?
In filtration applications of geotextiles, soil layers must be separated from each other while allowing water to flow freely. On the other hand, if the permeability of the geotextile is too low, fine particles may enter and clog the geotextile, causing groundwater to become trapped and generating hydrostatic pressure, which may lead to soil failure, rendering the geotextile ineffective. Conversely, if the permeability is too high and allows excessive soil particle migration, filtration failure may also occur. Therefore, geotextiles used for filtration and drainage must have an appropriate barrier function.
Needle-punched geotextiles are commonly used because their stable pore structure can effectively maintain a consistent water flow path.
Permeability and drainage: This technology helps remove excess water accumulated within soil structures.
High-permeability geomembrane materials can quickly direct water into drainage pipes behind retaining walls. This reduces the load of hydrostatic pressure exerted by groundwater on retaining structures.
In road engineering, pavement fabrics are often used to prevent water that would otherwise infiltrate the construction layers from being trapped within them. This helps prevent deformation and crack propagation to the pavement surface. Past pavement performance demonstrates the benefit of good drainage in extending service life.
Permeability and separation layer function:
Geotextiles serve an important role as separation layers. Their purpose is to separate two different soil types while still allowing water to pass freely from one side to the other. In this case, whether water can flow freely depends on the permeability of the geotextile. If the fabric does not allow water to pass through, water will be trapped between soil layers, and over time this will weaken the base gravel.
PP geotextiles and PET geotextiles exhibit good performance, such as stable permeability and long service life.
How material selection affects permeability :
Many materials show different permeability characteristics after being exposed to liquids. Polypropylene nonwoven geotextiles have higher permeability than many other materials. This makes them suitable for filtration and general drainage applications, especially in grouting operations.
Continuous filament geotextiles exhibit good permeability across various conditions. They have a reasonable and uniform pore structure that enhances water flow performance.
Thermally bonded geotextiles are reported to have lower permeability than the above types. This is partly due to their higher mechanical stability.
Permeability alone is not the only design factor for geotextiles; tensile strength and CBR puncture resistance are also important supplementary properties.
High permeability was once considered an advantage, but in terms of tensile strength, it performs worse than woven geotextiles.
These nonwoven geotextile products do not rely solely on high flow capacity. They offer many advantages in filtration and drainage and are ideal materials for soft ground applications. Their UV resistance and durability are also critical.
During most installation processes, geotextiles are exposed to sunlight regardless of slope angle. Therefore, for long-term use, geotextile materials and all geomembranes used in outdoor environments must have excellent UV resistance.