Some labs are doing shear tests (in addition to peel tests) on each track of double track seams of geomembrane liners. Naturally they are charging twice as much as for single shear tests on both seams. While this is one way for the labs to increase their revenues it is of doubtful benefit in assessing the quality of the seam. It has been my contention for some time that measurement of seam strength provides little useful information anyway, but nothing of any practical importance can be gained by testing each track.
Only adjacent geomembrane ductility is important in the shear test.
In-service shear stresses only act across both tracks. Peel test are done on each track to assess the quality of the bond on each track and since peeling stresses can be applied to each track in service. The same does not apply to shear stresses. I don’t believe it is necessary to do a shear test on each track. Geosynthetica.net offers space for an opposing point of view.
Labs are fighting the commodity pricing philosophy of testing just as much as manufacturers and installers. However, we now have over 20 independent labs that are accredited under the GAI-LAP. These labs have quality procedures and documentation in place in line with ISO 9002, and soon ISO 9000 and 1SO 17025 standards, to assure quality data for their clients. It is costly to have these systems in place. GAI-LAP accreditation is surely justification for these labs charging higher testing rates. And when a sample is shown to be outside specifications these results from a GAI-LAP lab should be believed without question. The staff at these labs will review data, and check any results that do not meet industry specification before they are sent out, just to ensure that they are not in error. The practice of requiring the lab to repeat tests that fail, at no cost, should not be necessary. If retesting is required the requester should be prepared to pay for them.
For example, in a recent situation a lab was asked to repeat a set of
failing tests (at their own cost) and the project engineer sent a duplicate set of samples to a second lab. Thinking ahead, the first lab also sent samples to yet a third lab. The first lab and the third lab both got the same failing results as generated during the first tests. The second lab was able to get passing results!! However, when faced with the three sets of reproducible passing results, the second lab found errors that resulted in incorrect data! Test results can be the basis of some very costly decisions – surely it is worth paying a little more to be assured you have reliable data – the first time?
