Throughout history, engineers and construction companies have struggled with weak soils - and all the challenges that come with building on them. Erosion and loose foundational soil made for uncertain construction projects.
It wasn't until the 1950s when the application of woven permeable fabrics - now known as geotextiles - was shown to significantly improve soil strength and retention. But it took another 20 years before Dr. J.P. Giroud first used the term "geotextiles" in 1977 at a Paris engineering conference. That's when the idea of using geotextiles to improve paving and construction projects began to really catch on.
Today, woven and non-woven geotextile fabrics have changed the way civil engineering projects are executed. Now geotextiles are made from more than 400 different materials, giving the fabric a range of uses, from paving roads and filtering drainage to erosion control.
Geotextiles offer useful, simple and cost-effective solutions for improving the performance of almost any pavement or soil. Geotextiles are so important that there are annual engineering conferences centered on their specific design and use. There's even a scientific journal, Geotextiles & Geomembranes, that published peer-reviewed novel research on this specific niche.
Geotextiles are permeable fabrics. When used in soil, they serve generally five different functions:
• Separate: Placing a boundary between two things or areas
• Filter: Allowing a fluid to flow while removing or catching particulates
• Reinforce: Providing structural enhancement to an area
• Protect: Often in conjunction with separating, placing a boundary over soil or a foundation
• Drain: Removing fluid from an area or redirecting it to another area
Geotextiles are either woven - looking much like a mail bag - or non-woven, in which case they could be needle punched or heat bonded. Non-woven geotextiles may look like felt or iron felt. To put it simply, geotextile fabrics help make soil - and what rests on the soil - more structurally sound, strong and durable.
Geotextiles provide strength and durability by separating a foundation or construction from underlying soil. For example, if pavement is laid on dirt, over time the lowest layer of the pavement will disassociate as the soil infiltrates the payment. This leads to weaker pavement, reduced service life and greater maintenance costs.
Using a geotextile layer to separate the pavement from the ground helps maintain the structural integrity of the pavement over time. This is especially important in climates that undergo successive episodes of freezing and thawing. Geotextiles also help prevent the underlying soil from contamination, as well as the pavement from settling if the subgrade beneath the pavement sinks or shifts.
Some common applications of geotextiles and how the materials help:
Reinforce weak or aging soil underneath roads, railways, airfields and embankments
Filtrate subsurface drains and rock seawalls
Drain and protect the lining systems for landfills and waste containment
Reduce beach erosion from wind and water in coastal applications
Protect the ground at stadium events from damage when temporary staging is used
Let's examine the structural difference between woven and non-woven geotextiles to better understand the specific application of each.
While woven and nonwoven geotextiles can be made from polypropylene - a thermoplastic polymer - they each go through a different manufacturing process, resulting in unique product characteristics.
Specifically, woven geotextile fabrics are manufactured by weaving narrow strips of film together to form one large piece. This results in a tough fabric that has a higher load capacity. That's why woven geotextiles are used commonly for ground stabilization in roadway construction projects. However, the drainage characteristics for woven geotextiles are typically not as good as they are for non-woven geotextiles.
Non-woven geotextiles are felt-like fabrics manufactured by bonding with needle punching or, in some cases, heat. This allows the fabric to have excellent filtration and drainage characteristics. Since non-woven geotextiles have higher permeability, they are the ideal choice for subsurface drainage applications such as pond underlayment, ditches, around pipes, erosion control or in any application dealing with high levels of runoff or site drainage.
Geotextiles are used most frequently in filtration. Water or another fluid flows through the geotextile, and particles that are larger than the size of the weave are trapped by the geotextile. The concern in filtration applications is that the geotextile will eventually become clogged and will need to be replaced over time.
In drainage applications, geotextiles can facilitate the movement of liquids. Here, non-woven geotextiles are preferred. They're designed typically for short-term applications to wick or otherwise drain liquids from a particular area.
Geotextiles also offer erosion control solutions - they're often used to firm up soil surfaces. The geotextile can help protect the surface from the eroding effects of wind and rain. It can also help reinforce soil, for example, along embankments that would otherwise face a greater likelihood of erosion and degradation.
This is becoming increasingly important in shoreline and close-to-shore installations. Geotextiles can help guard against wave erosion and have been used in Australia, Germany, the United Kingdom and the USA.
Geotextiles can also help provide a barrier to moisture when other chemicals are added to their composition. This application - often used in paving - reduces the amount of water that gets below the pavement and into the foundation or subgrade.
In addition, geotextiles can provide a filter fence - which when reinforced is known as a super silt fence - to protect streams, rivers, lakes or other bodies of water from runoff sediment that would otherwise contaminate the water source.
One geotextile often chosen for its filtering properties is GeoTac. GeoTac waterproofing membrane is a fabric that you can peel and stick where you want. There are variations that include polyester fibers, giving GeoTac extra durability. GeoTac is made of a polymer waterproofing adhesive that's bonded to a non-woven polypropylene material.
GeoTac has an adhesive layer, which will bond to a surface and prevent or limit moisture. It can also provide a layer of protection to surfaces during construction operations.
You'll find GeoTac used in parking lots when repairing cracks in the asphalt. It's also used in box culverts, which allow water to flow under roads, railroads or similar obstructions. It meets the regulatory requirements of most state highway departments for strength and waterproofing pavements and bridges.
GeoTac comes in different widths - from 12 inches to 48 inches - and is wound on rolls of 50 or 100 feet for easy deployment. You unroll it onto the desired surface and remove the GeoTac liner so that it can adhere to the surface. For even greater flexibility, GeoTac HS - the extra durable version of GeoTac - is resistant to the heat in asphalt pavement at temperatures up to 350 degrees Fahrenheit.
The selection of the correct geotextile for the application is critical to the long-term performance of the structure. Some factors to take into consideration include desired flow rate, strength, pore size and type of aggregate being used.
One common question in selecting a geotextile pertains to the size of particle that will pass through. This is measured nominally in microns. That's about one one-hundreth of an inch.
It's best to be supported by experts when deciding which type or types of geotextiles you'll need for your application. That's how Daniel B. Krieg can help.
Our company carries both woven and nonwoven fabric in several lengths and widths. Our polypropylene woven fabric is rot-proof, resistant to most chemicals and virtually unaffected by acids and alkaline. Our non-woven fabrics have a three-dimensional pore structure and are highly water-permeable, as is necessary in many geotextile end uses.
We also carry a variety of other erosion control products, such as silt fence, silt sacks, straw blankets, coconut blankets, turf reinforcement
Geotextiles have numerous and versatile uses in construction, paving and many other applications. They're important because they can:
• Improve drainage.
• Extend the life of pavement and other structures.
• Reduce maintenance costs.
• Prevent contamination of foundation soil.
• Provide a filter to help maintain clean water sources or prevent contamination.
You'll find geotextiles used in underground stabilization under railroad tracks, underground drainage providing a foundation for pipes and pillars, embankment protection, seawalls, bridge abutments, sports fields and numerous other situations.
Now, geotextiles are beginning to benefit from the embedding of fiber optics. This offers real-time situational awareness of the installation. With advanced monitoring, engineers can better anticipate when preventive or proactive maintenance may be required.