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This
article will cover the basics for sewing geotextiles, concentrating
on the field sewing installation. However, sewing can also be done
off-site for certain applications.
The
first requirement is to determine the seam strength, which should
be done by an experienced engineer. The geotextile material, its seam
type, and the thread stirches per inch are all factors in determining
seam strength. Possible seam types, stitch types, and sewing tips will
be covered.
There
are 3 basic seam types:
1.
Prayer Seam
2. 'J' Seam
3. Butterfly Seam
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Prayer Seam |
'J' Seam |
Butterfly Seam |
The
engineer will decide which seam to use based on the job requirements.
Other
sewing factors to be determined include stitch type and stitch length.
The stitch type is normally a 401 stitch (or called 2-thread double
stitch).
This
stitch provides the security and strength needed. Typical applications
will call for either one or two rows of 401 stitch and obviously two
rows of 401 stitch will be stronger than a single row. When sewing
the 401 stitch it is best to sew it with a machine that will allow
you to set the stitch length to the desired setting for that fabric.
Stitch length is usually defined in terms of SPI (or stitches per inch).
If the SPI is too short (more stitches per inch) then perforation
can occur and cause problems. If the SPI is too long (less stitches
per inch) then the seam may not be strong enough.
Above: Stitch type used in field seaming of geotextiles
Tips
for field sewing:
1.
Use three people. The first person holds the fabric and joins the seams
according to seam type. The second person sews, while being careful
not to allow the weight of the fabric to put excessive stress on the
sewing machine needle, causing it to break. The third person holds
and supports the fabric after it has been sewn.
2.
Use a machine equipped with top-feed for sewing; it makes it easier
to guide the sewing machine. Without a top-feed, the operator will
have to pull more on the machine, thus increasing fatigue.
3.
Keep the wind from blowing the thread off the cones. One trick is to
use ladies' nylons; snip off the toe and put the nylon over the thread
cones to keep the thread in place.
4.
Have a backup sewing head at the job site in case something goes wrong
with the one in use. It is less expensive to have an additional machine
than to have down time.
5.
The sewing machine is not indestructible. Make sure you keep it clean
from debris and well oiled and monitor the needle condition daily (change
if blunted or burred).
For
more information on sewing geotextiles please go to www.unionspecial.com or
call Union Special Corporation at 1-800-344-9698.
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