Understanding Woven Geotextiles
Woven geotextiles are fabrics that are typically flexible, exhibit high strength, high modulus, and have tight openings in the weaving pattern. They are distinguished from nonwoven geotextiles in that they have low elongation properties (as low as 5% and 25%) and they do not drain well. Generally speaking, woven fabrics are more plastic-like in feel and appearance. While they are relatively impermeable and don’t offer drainage, they do have a very high load capacity and are commonly used for roads and parking lots.
Woven geotextiles are manufactured to ASTM International product standards to deliver high tensile strength and low elongation. Contractors count on these attributes, and routinely place these fabrics on top of areas where it’s difficult to achieve design compaction or soils are very wet. Woven geotextiles are often used when soft soils have a California Bearing Ratio (CBR) < 1.
Woven geotextiles are made by interweaving thousands of material threads on large, specialized looms. Most contractors opt for woven geotextiles made from one of two common thread types- monofilament polyester or polypropylene. Both material types work well, but you should consult with your White Cap expert to determine which is best for your application. Other thread types include multifilament, slit-film, fibrillated slit-film, or a combination of the threads.
Wovens are Strong and VersatileFor large, complex projects, engineers can seek help in matching the unique soil conditions to not only thread type, but the fabric’s weave pattern. Manufacturers weave geotextile practically the same as cloth. They can program to weave the fibers in a wide array of patterns. Tighter patterns can result in greater strength. Looser patterns allow more flexibility in the cloth. Some weave patterns can be aligned to anticipated drainage considerations to allow water, but not silt to pass through. There are many options and most all have a direct influence on the physical, mechanical, and hydraulic properties of the fabric.
But for most applications, contractors should refer to a woven geotextile’s listed tensile strength. This rating is measured with the ASTM International test method to determine the fabric’s resistance to breaking under tension. For example, if you are constructing a temporary road for large construction equipment, you would need a woven geotextile with a higher tensile strength than if you were constructing a golf cart path. Unlike its nonwoven counterpart, the weight of a woven geotextile is seldom listed because these materials are usually used to offer separation and reinforcement, and thus are not weight dependent.
Woven geotextiles also have become popular in vertical applications and are effective as silt fences. They are often listed as a Best Management Practice and reduce the chance of release of suspended solids into drainage areas. They also protect water quality by retaining soil and allowing water to filter through the geotextile. Woven geotextile silt fences are strong and can hold back large volumes of material.
Another use of a woven geotextile vertical barrier is a leachate collection system. These materials are resistant to ultraviolet degradation and biological clogging.
Woven Geotextiles Benefit Contractors and Owners
Contractors can effectively shorten roadbuilding schedules and minimize construction material purchases. During and following construction, roads supported by woven geotextiles are less subject to rutting, reducing maintenance costs. Owners benefit because the resulting structure is sustainable and can be measured as reducing the project’s carbon footprint.
Woven geotextiles arrive at the jobsite on large rolls, allowing contractors to easily lay the fabric flat. When placed, they effectively become a barrier, covering wet, weaker, or less desirable subgrade. The fabric then separates when aggregate or other materials are placed on it. The geotextile’s tensile strength supports the covering material by distributing its mass across the fabric’s horizontal plane. The durability of the geotextile ensures both long-term separation of the materials and stabilization of the road or slab placed on grade.