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GMA Techline’s 3rd 500 Q’s-and-A’s

February 1st, 2011 / By: / GMA Techline, Updates


The GMA Techline was initiated in September 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 provided.

These answers have been addressed to the best of our ability and have been provided generally by Robert Koerner with noble assists by Grace Hsuan (generally polymer related) and George Koerner (generally laboratory or field related). Jamie Koerner assisted in assembling the data and curves provided in this summary report, and Marilyn Ashley provided information services.


Regarding the activity level, quarterly reposts are provided to GMA with selected questions-and-answers running regularly in Geosynthetics magazine. And now we have questions stemming from those answers provided in this magazine—in this regard, a second generation set of questions.

Shown in Figure 1 is the quarterly trend of good questions. Figure 1: Q&A activity of GMA Techline, cumulative good questions By “good” we mean that solicitation-type questions and non-geosynthetic questions have been culled out to the totals presented. The trend of Figure 1 clearly shows a slow growth until mid-2007, when the trend increased. This was stimulated by having direct access on several websites including GSI’s. Since the beginning of 2008, the trend has been consistent with about 35 questions answered per month.

Information regarding questioners

Figure 2 indicates that the vast majority of questioners are from the USA (about 66%), which is similar to the first 1,000 questions. Figure 2: Worldwide location of questioners (each bar represents 500 Q’s & A’s)

Figure 3 presents the occupation of the questioner, with designers and consultants the majority at about 46%. A little more than half that number were manufacturers and their representatives at about 25%. Figure 3: Occupation of Questioners (each bar represents 500 Q’s & A’s)

Analysis of specific questions

Figure 4 shows that geomembranes continue to generate the most questions, about 41%. Figure 4: Type of geosynthetic material (each bar represents 500 Q’s & A’s), number of inquiries per 500 Q’s & A’s

Geotextiles and general questions on all geosynthetics, or on no specific type of geosynthetic, were next at about 15% each. Geogrids had a steady number of questions, at about 10%. Geosynthetic clay liners, geonet/geocomposites, geo-others (e.g., geofoam, geofibers, geowebs), geopipe and geoerosion control materials (GECM) accounted for a combined 19% of the total.

Figure 5 pertains to the category of questions asked.Figure 5  General category of questions (each bar represents 500 Q’s & A’s), number of inquiries per 500 Q’s & A’ The design/specification category saw a strong rise to approximately 28% in this “3rd 500.” These questions were extremely broad, some requiring far more time and space than could be provided. Oftentimes such questions were answered by sending a technical paper(s) on the topic.

As seen, questions on lifetime (21%), general information (17%), strength (13%), installation (12%), seaming (6%), and clogging (3%) were also of interest.

The lifetime questions were very broad, from the usual “how many years?” to effects of pH, chemicals, radioactivity, freeze/thaw, etc.

Regarding installation questions (which were often difficult to separate from seaming questions), most were answered by our opinion or occasionally by referencing a technical paper or design procedure.

Temperature (both hot and cold), placement seaming, and backfilling questions were frequently asked. In such cases our answers were felt to be conservative and often did not satisfy the questioner who came back with follow-up questions. We generally went back and forth until one party or the other wore out!

This, of course, leads to the perceived difficulty level of the questions, which were arbitrarily put into five categories. See Figure 6, where “one” is the hardest and “five” is the easiest. In total, there were 15 “ones” (vs. 14 “ones” in the first 500 questions and 12 “ones” in the second 500 questions). Figure 6  Difficulty level of questions (each bar represents 500 Q’s & A’s), number of questions per 500 Q’s & A’s


In closing, we hope to continue to report to GMA at 500 Q-and-A increments to observe trends and, in so doing, to track the technical aspects of the geosynthetics.

Bob Koerner | GMA Techline

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