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The GMA Techline and its 4th set of 500 Q’s & A’s

News | June 1, 2012 | By:


The Geosynthetic Materials Association’s (GMA) Techline was initiated Sept. 1, 2004, as a free worldwide service to answer questions involving the many aspects of geosynthetic materials.

From the outset there were no constraints placed on the questioner or their questions. GMA contracted with the Geosynthetic Institute (GSI) for answers and, again, there were no constraints placed on the answers that were provided. These answers have been addressed to the best of our ability and have been provided generally by Bob Koerner with assists by George Koerner (generally laboratory or field related) and Grace Hsuan (generally polymer related). Jamie Koerner has assisted in assembling the data and curves provided in quarterly reports and in this summary report. Marilyn Ashley provided report preparation.

Activity level

Regarding the activity level, quarterly reports are provided to GMA with various selected questions and answers, that regularly appear in IFAI’s Geosynthetics magazine. Recently, we have had questions stemming from the answers that were provided in the magazine; in this regard a second generation set of questions. Since the beginning of 2008, the volume of questions has been consistent, about 32 questions per month.

Sources of questions

The majority of questioners are from the U.S. (about 64%) which is down slightly than previously.

Regarding the remaining 36%: Europe–9%, Near East Asia–9%, Far East Asia–5%, Canada and Mexico–4%, Latin America–4%, Australia and New Zealand–3%, Africa – 2%.

Regarding occupations, designers and consultants offered the most questions, followed by manufacturers and their representatives.

Overall, the percentages are as follows for this fourth set of 500: designers/consultants–48%, manufacturers/representatives–21%, regulators/agencies–13%, installers/contractors–7%, owners–7%, academia–4%.

The largest gain in questions came from the regulatory/agency group and the largest loss from academia (i.e., faculty and students).

Analysis of questions

Questions about geomembranes continued as the most frequently asked category of geosynthetics. Questions regarding geotextiles have decreased in each set of 500 questions.

The category on the rise is geogrids. But it should be mentioned that a large number of questions on walls, berms, and slopes were in this group and they were categorized as “geogrid-reinforced,” whereas some may have been geotextile related.

Geonets, GCLs, and geosynthetic erosion control materials each had increased questions over previous reports. The geosynthetics-in-general category addressed questions such as landfill cover systems and pond liner systems where multiple geosynthetics are involved.

The percentages by product: geomembranes–39%, geosynthetics-in-general–15%, geogrids–14%, geotextiles–13%, geosynthetic clay liners–8%, geonets and geocomposites–6%, geocells–2%, geosynthetic erosion control materials–2%, geopipe–1%.

Difficulty of questions

The issue of question difficulty is, of course, extremely subjective. A question on antioxidant chemistry is difficult for a geotechnical engineer, while the idiosyncrasies of using peak or residual shear strength might be different for a chemist and vice versa! Between the three of us (Bob, George, and Grace) we hope we got the answers right.

Nevertheless, the grouping was made on a sliding scale of 1 (hardest) to 5 (easiest). The easiest (at 6%) were mainly requests for papers and directions of where to retrieve information. Category 3 (at 61%) were considered to be good state-of-the-practice questions, with category 4 (22%) somewhat easier and category 2 (8%) requiring some digging on our part.

Lastly, category 1 (3%) were really difficult for us and we did our best. Two of these questions even spurred us to do new research projects for which we are thankful.

Concluding comments

We usually respond to the Techline questions ( within two days and sometimes within hours.

This engenders the questioner to come back against our answer with another related question. It sometimes goes back-and-forth for several iterations but this is the nature of such electronic dialogue.

In this regard, the Techline is analogous to questions asked during webinars, such as those we are involved with on behalf of the American Society of Civil Engineers (ASCE). Questions during these webinars are asked anonymously by those participating and the presenter sees them on a split-screen and answers accordingly. At the close of each of these webinars, we are now suggesting that participants go to the Techline for further interaction. The two efforts appear to be quite complimentary and we enjoy doing both.

Bob Koerner, Ph.D., P.E., NAE, is the director of Geosynthetic Institute (GSI) and is a member of Geosynthetics magazine’s Editorial Advisory Committee. GSI: +1 610 522 8440,
George M. Koerner, Ph.D., P.E., CQA, is the director designate of GSI,

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