Woven versus nonwoven geotextiles 9

[mollyengineer]

Is there someone out there who could explain the applicability of woven versus nonwoven geotextiles? Benefits to each? What types of projects would each be appropriate on?

 

[Focht3]

Woven:
advantages - cost, strength, stiffness
disadvantages - easily "opened" by angular aggregate; poor filter, so it may not keep layers separate

Non-woven:
advantages - excellent filtration and separation properties
disadvantages - more expensive than a non-woven (only a little); not as stiff (but can be strengthened and stiffened by making it thicker and reinforcing it)

Do you have a specific application in mind?



Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.

 

[NewcastleEngineer]

I will attempt to answer your question as best I can and a s briefly as I can.

Woven fabrics are individual threads (monofilaments, multifilaments or fibrillated yarns) or slit films and tapes that are actually woven on a loom. Typically, they have a very uniform appearance.

Non-woven geotextiles are made using synthetis filaments or fibers that are continuously extruded and spun, blown or placed on a moving belt. These items are then needlepunched or heat bonded into a nonwoven mass.

Typically the non-woven fabrics are used in filter and separation applications. Whereas the wovens can be used for stabiliztion, reinforcement, as well as, filtration and separation. However, the correct nonwoven and woven fabrics must be selected for each individual application.

A very helpful reference on geosynthietis is "Geosynthetic Engineeering" by Robert D. Holtz, Barry R. Christopher and Ryan R. Berg published in 1997 by BiTech Publishers Ltd. in Richmond, British Columbia, Canada. This book is very good at explaining design and selection of geotextile fabrics for various applications.

I hope this helped.

 

[layfieldman]

There are 5 typical functions that geotextiles perform: filtration, separation, drainage, protection and reinforcement. You should design the geotextile, woven or non-woven, depending on what your primary function is. The only one in my list that wasn't covered by the others is protection, typically for geomembrane liners in landfill applications.

 

[SirAl]

As NewcastleEngineer has noted, text books about geofabrics have been writen. It is a broad topic to be sure. In my experience, if you were to ask 10 engineers/contractors of their opinions, you would likely recieve a range of differing responses as individuals have their personal preferences based upon experiences, etc. My personal bios is to apply a woven product in structural applications such as roads/embankments where some secondary 'reinforcing' benefit may be realized (recognizing that geogrids are available as better reinforcing tools in granular base, earth retaining structures etc.) Conversely, it is my perception that non-woven fabrics are better filtering or separating products that can function under a wider range of deformation than that of a woven product.

 

[ga414]

I a believe the nonwoven may be of higher quality re. filtering a select range in grain size. The needle punch used in mfgr better controls the size openings.

 

[bbarrett33]

Woven vs nonwoven. So many misconceptions exist about the role of inclusions in soil. I noted Sir Al thinks geogrid is somehow superior to other inclusions. Rarely the case. We have built reinforced soil structures with bed sheets from J. C. Penny to illustrate that it is the presence of the inclusion, not the stregth/stiffness. We have built many walls with wovens. So has the USFS in the 1970's. Even the word "filtration" is bogus. Filters fail. That's what they are there for. Wovens act as permeable restraints to maintain equilibrium in the soil structure. If there is particle migration, either the particles will go through a filter, or the filter will eventually fail. The idea is to prevent particle migration. Nonwovens do this best.

What happens in a soil environment is that each of the fibers in a nonwoven is closely confined by the soil mass. The in-air properties are very different than in-soil properties. All the inclusions, including bedsheets, behave very stiffly up to very high levels of loading. None of the mathematical models currently in use reflect this. Most are in conservative error by factors up to 20. Yes, 20. We spent over 25 million in research to learn this.

We have built over 200 million dollars worth of GRS features. Walls, abutments, piers, barriers and more No one pays much attention to us. It must be that we use generic materials and designs, counterflow to the proprietary mainstream.
So if you are using grids for stiffness, then why not something that is really stiff like chain link? If you want reinforcement, wovens typically serve best, when cost is a factor. If you want particle restraint, use nonwovens. If you want filtration, you don't understand the question.

 

[layfieldman]

bbarrett33

I would be interested in what you are talking about. I wonder if this was state financed research or university? Please let me know where I can find some more information. Also, have you heard of Dr. Bathurst and his research with full scale retaining walls at the Royal Military College (Canada)? He has shown that present design techniques are typically conservative, requiring double the actual required reinforcement.

 

[bbarrett33]

The work was funded by the Colorado Department of Transportation and the FHWA. Most of the work was done by the University of Colorado/Denver. We began in 1972 and followed the work by the USFS. Those folks wrote the first design manual, 1978. Dick Bell and Oregon State were also involved. We built a 300 foot long, 15 foot high test wall in 1982 with non-wovens. Dick Bell was a coresearcher. We built a large frame and built several full scale walls, larger than at RMC. We hosted an international prediction symposium in 1991 where folks from 12 countries predicted the performance of two full scale GRS walls, one built with clay soil and the other with Ottawa sand. We showed the falacies with current design methods. We have built GRS walls with tire shreds as backfill. We built a huge bridge demo and held another international symposium. We showed that GRS structures are superior abutments in many applications. No bump, last longer, cost less. We cooperated with FHWA in building several full scale abutments. Now we have NCHRP 12-59 that is compiling all this previous work into a design/construction guideline for GRS abutments. There are wheelbarrows of good data out there, but it does not seem to make it into AASHTO/FHWA/NCMA guidelines. All that stuff about stiffness, drainage layers, embedment, connection strength, creep, footings and more are artifacts of older thought. GRS structures can be built stiffer and stronger than AASHTO and NCMA designs and for about 20% less cost.

I don't say much about this. We are making a lot of money with this knowledge. The shame is that the taxpayers who paid for our education are seeing little benefit.

Check

http://www.yenter.com

and

http://www.soilnaillauncher.com