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Geotextiles 1

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Zambo

Civil/Environmental
Jun 5, 2003
697
I would like a quick opinion, based on the limited information I am giving here, on the best (i.e price and performance) type of geotextile to use on my project.

We have a site which is reclaimed land, silt/clay at depth and sand for the upper 5m. The site needs access roads and car parks with general industrial type loadings - say trucks with 40 tonne loads / 10 tonne per axle loads.

The roads/car parks will be constructed from graded crushed limestone max size 50mm. The proposal is to grade the sand to level and compact, lay a geotextile, fill with 375mm of crushed limestone in 2 layers, then lay 100mm of asphalt.

My question is whether to use a non woven geogrid ("Netlon type") geotextile or to use a woven ("Terram fabric") type. The important factors are perfromance and cost which includes the cost of the geotextile and the expected saving on thickness of subbase.

Any suggestions?
 
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Unless you have a CBR of 4 or less and also use high strength woven fabric, my information shows no savings of significance.

Manpower cost to lay the stuff, stitch sections together or overlay joints add to the area unit costs.

Think about the future. Will any trenches be dug later? This stuff is agony for those folks then.

From your information I'd say you don't need it.
 
The difference between woven and non-woven geotextiles is that non-woven is used as separation between differing soils and woven actually provides tensile strength.

Therefore, if your goal is to use the geotextile as a reinforcement layer, then you need to go with a woven fabric. However, there are woven fabrics that provide very little tensile reinforcement. It is important to use the correct fabric for the application.

Generally, woven fabrics are more expensive.

All that said, I tend to agree with oldestguy. The real benefit that you would get is that if the reclaimed land (fill) was not placed in a controlled manner. With woven geotextiles you would have more uniform settlement and, therefore, less potential for cracking of the pavement.

Do you have information on the placement techniques of the filling for the reclaimed land? Do you have soil boring information that indicates the relative density from one location to the next?

If you feel the fill was place in a controlled manner and you don't see much variation, then you probably don't need the geotextile.
 
Eric1307,

thank you for your post. The specified geotextile is a non-woven geotextile and is intended as a separation between the sand and the crushed rock sub-base. I think that this separation should have an effect in reducing the required crushed rock thickness. With a clay subgrade there should be a significant saving but with sand I do not know if any reduction in thickness would be sufficient to make the geotextile cost effective.
 
If you have a well graded base course (graded crushed limestone), there is no need for a separating layer of fabric.

The filtering is done by the fines in the mix.

Non woven fabric will stretch maybe 200 percent of original dimension before breaking and that provides insignificant reinforcement and thus insignificant affect on base course thickness needed.

In Wisconsin a well graded crushed rock base course over a
sand sub-base has been a standard pavement section for years and no need for a separating layer ever came up to my knowledge.

With the new single sized upper base course layer (to prevent rigid pavement faulting) there still is no
separation material used on the well graded base course material below.

 
The sand should be a good subgrade for the pavement. Like others said, there is likely no need for the fabric. Quite honestly, I am not so sure you need 4.76 inches of stone base for that either. If you really want to save money, spend a grand, or so, and have someone get you information on the sand (i.e. AASHTO class. and CBR or Hveem). Next step is to get some recommendations as to whether you need to improve the subgrade (may be cheaper than fabric). Also, if the materials are loose, look into cement stabilization. You may reduce your overall section enough (including eliminating the fabric) to pay for it, and end up with a better product for the long run.
 
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