GT seam strength

From the GMA Techline

RE: GT seam strength
We are starting to see more specs requiring 90% retention of original strength for seam strength on geotextiles.

Is this common in the industry?

What is the standard retention value?

And do these values change between monofilament, slit film, and nonwovens?

Thanks
(Dan | South Carolina)

Reply: At 90% of fabric strength you are flirting with disaster. The only savior in this regard is that ASTM allows the seam test specimen to be 2in. wider than the wide-width nonseamed specimen (it is 10in. vs. 8in.).

At the core of the situation, however, is that any seam will result in the lowering of a fabric’s as-manufactured strength. Some of the needles simply must penetrate fibers or filaments, resulting in the reduction. Now the issue is: How much reduction?

The answer to this is another question: How strong is the original unseamed fabric? For low-strength fabrics (less than 100lb/in.), the seam efficiency is about 90%. For intermediate-strength fabrics (about 250lb/in.), it drops to about 75%. For high-strength fabrics, (about 500lb/in.), it drops to about 60%.

For fabric strengths of 1,000lb/in., it is about 50% efficient. After that you should really try to design around sown seams. … Bob Koerner

P.S. I have a laboratory generated curve that I will send describing the above efficiency situation. -BK-

Bob Koerner | GMA Techline