Choosing the right geotextile fabric is critical for civil engineering and construction, both for pavements and for soil stabilization. Of the many properties which geotextiles may possess, tensile strength stands at the heart of the question of performance under stress.
The tensile strength quantifies “how strong a geotextile may be pulled before it breaks,” and is expressed as above, commonly in kilonewtons per metre (kN/m). Typically a geotextile will have high tensile strength to support heavy loads and resist tearing; therefore, for most demanding applications, a geotextile of high strength is desirable.
Basically, tensile is the property which ensures that the fabric can remain stable under wheel loads, loads from construction equipment and pressure from soil. Using a geotextile with inadequate tensile strength will result in deformation and/or tearing of the fabric acting to lead to costly repairs and possible issues with safety.
Types of Geotextile Fabrics
Commonly, geotextiles are divided into two types, with each having a different and distinct range of mechanical properties:
- Woven Geotextiles. Typically manufactured from polypropylene or polyester filaments by means of a power loom, woven fabric has comparatively high tensile strength properties and low percentage elongation. Woven geotextile fabric is used for a wide range of applications, including reinforcement against loads such as under highways, for slope or embankment stabilization and as railway sub-grade solution.Heat-bonded geotextiles – These provide a uniform thickness and dimensional stability, but tend to have lower puncture resistance.
How to Choose Geotextile Properties – Tensile Strength
The profile of geotextile selected will depend upon the project conditions and performance expected. It is good practice to consider:Load & Traffic. Roads and highways carry heavy vehicles. Fabrics used in these situations require high tensile strength so that they are used effectively and deflection does not occur. Railway embankments of heavy road construction also require strong geotextiles to allow for dynamic loading in this type of application.Soil type. Softer soil such as clay and silt will allow more stress to the geotextile and should ideally select a geotextile of higher tensile strength when used in conjunction with these soils, thus increasing the fabric strength and reducing its chances of failure;Length of usage for project. Long term infrastructures can be enhanced further when the geotextile will be less pressurized into greater machines or degrading by using a stronger tensile fabric;Stress/Environmental Conditions. Fabrics subjected to UV rays or extreme temperatures will degrade due to chemical reactions. Select geotextiles that will be able to absorb the stress of loading through greater tensile strength.
Reading Tensile Strength Specifications
As there are no manufacturing standards, refer to the supplier’s geotextile technical datasheets as a guide. Standard tests include breaking strength of the fabric using tests such as ASTM D4632, and EN ISO 10319. Not all are the same. Know which is used, and therefore what smaller individual figures they indicate. Breaking Strength. The actual strength of the load that the fabric can carry before rupturing. This is the most important measure to look at where loading is of utmost consideration. Elongation. The fabric’s stretch before the breakage; a modest indication can absorb dynamic loads better.Puncture Resistance – Different from tensile strength, this important property comes into play with concentrated loads; the greater the puncture resistance in most cases, the higher the tensile strength of the fabric.
Which Type of Fabric Must be Matched to the Application
Selecting geotextiles for a project:
Roads – Woven geotextiles having a high tensile strength and adequate puncture resistance are indicated to prevent rutting and provide long term support of the subgrade.
Drainage and Filtration – Non-woven geotextiles with some tensile strength are adequate in most cases. The primary use of the fabric is a substitute for gravel, controlling the flow of water while retaining some soil particles.
Erosion Control – Slopes, and riverbanks require some tensile strength, but most of all flexibility. Needle-punched fabrics provide the best – percent of elongation of 50 or more.
Separation Layer – Geotextiles separate two different types of soil/aggregate combinations when subjected to high loads preventing intermixing. Adequate tensile strength will ensure the layer is kept in place over a long period.
Look at This in Addition to Tensile Strength
Puncture = CBR Puncture Strength is a measure of a plastics resistance to puncture with concentrated loads. Most important for roads and industrial use.
Permeability and Flow rate – high. Required on drainage fabrics to extensively drain the soil and maintain a “drain” effect, easy transfer of water from one channel to another. Typically larger flow rates are found with some non-woven fabrics.
UV – for fabrics used outdoors, UV resistance is a factor over a long period. Tests have shown most geotextiles maintain a large percentage of tensile strength.
Chemicals – some geotextiles are resistant to acids and alkalis. Used with wastewater, industrial uses.
Roll Width/Length – fabric can be rather wide reducing overlaps that could tend to reduce performance, larger roll lengths too help.
Now for Practical Hints on the Selection Process
Select geotextiles on site, practical considerations, including availability which must be obvious. Look for particulars here and in other specifications.
Factory Datasheets – must be read carefully both as to actual minimum strength and elongation, ie. better in practice to eliminate.
Soil/Load condition – inspect with care so as to avoid over-specifying or under. If combining a layer of high strength woven with a layer of non-woven for drainage, mix widths proceed carefully.
Leave some in, not too large a factor: the strong fabrics will be reliable and as a bonus, minimize maintenance.