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Questions and answers from the GMA Techline
I have a colleague who is insisting that we build a pond’s embankment extension by welding new geomembrane to an old one on the “slight” slope (really somewhere 1:4 ratio). I am arguing that we should do welding only on the horizontal part of the pond, between its breaking point and anchor trench, but I cannot explain to him why we can’t weld on the slope. (My arguments that slopes are the part where geomembrane is affected by increased forces aren’t working.)
What can I say to an engineer who is trying to specify welding on the “slight” slope?
Robert | New Zealand
The fundamental reason for not welding horizontally on a slope is that a seam is never as strong as the sheet material it is joining. That said, welding of geomembranes usually results in 80-90% of the parent material in shear testing and about 60% in peel testing. For very long slopes, it is done so long as the horizontal welds are staggered across the slope. It is also done going around corners and for other detailed work. If this is not the case, then you are better off welding on the horizontal base section of the pond.
Regarding your comment that the geomembrane is in tension while it is on the slope—that is not good. Geomembrane design should be such that the material does not have tensile stresses in it, and on slopes it is important that the frictional strength is higher than the slope angle it is resting on. Hope this helps.
Bob Koerner | GMA Techline