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GMA Techline’s first 500 Q’s-and-A’s

Q&A: GMA Techline | August 1, 2008 | By:


The Geosynthetic Materials Association (GMA) introduced the GMA Techline on Aug. 31, 2004, as a service to those involved with, and interested in, geosynthetics. The Techline is one of the educational services offered by GMA, with the goal of providing fast, free, and direct answers to technical questions about geosynthetics.

GMA contracted with the Geosynthetic Institute (GSI) to provide answers to questions that were posed to the GMA Techline via E-mail. From its inception, there were never any constraints placed on the content of the questions nor on the questioners’ affiliations or geographic location. With the casting of such a sweeping net, however, many nongeosynthetic questions and even some completely off-target questions, including political, social, and financial queries, have been received However, all of these are discounted in the data analysis to follow.

As of May 1, 2008, there have been 500 “geosynthetics relevant” questions asked and answered by personnel of the GSI (mainly by Bob Koerner but also by George Koerner and Grace Hsuan). A sampling of the most interesting question have been featured in Geosynthetics magazine (October/November 2006, June/July 2007, October/November 2007, April/May 2008, and scheduled for October/ November 2008).

This report addresses the following 6 topics: 1) activity level and promotion, 2) location of questioners, 3) occupation of questioners, 4) type of geosynthetics, (5) category of questions, and (6) difficulty level of questions.

Activity level and promotion

The number of inquiries each month has grown from less than 5 to more than 40 “geosynthetics relevant” questions. Since its inception, the program has been promoted to specifiers, contractors, and civil and geotechnical engineers through a variety of venues.

The service is prominent on and has been promoted through advertising in publications such as Geosynthetics magazine and NACE News (the publication of the National Association of County Engineers). The Techline has also been a service featured in GMA exhibit booths at various conferences serving the geotechnical, water, waste and erosion control industries. In March 2007, the Techline received increased exposure when a link was placed on the GSI Web site. An immediate increase in questions was observed. Questions currently are answered at a rate of more than 40 per month and trending upward.

Worldwide location of questioners

GMA is a trade association with market influence primarily in North America. Not surprising, the majority of questions have been generated in the United States (66%), Figure 1. Figure 1 | Wolrdwide location of questioner

The remainder are indeed worldwide and some commentary is in order regarding them. In the rest of North America, the questions are equal between Canada and Mexico. In Latin America, the ordering for number of questions is: Colombia, Peru, Brazil, and Chile. In Europe, the majority of questions are from the United Kingdom, followed by Poland, Czech Republic, Turkey, and Serbia.

Questions from Near East Asia are evenly divided by countries in that region; all have been included. From the Far East, the large majority of questions have come from India. Interestingly, no questions have been received from China, Korea, or Japan. Several excellent questions, but relatively few in total, have been from Australia. The few questions from Africa have been from either South Africa or Egypt.

Occupation of questioner

It was relatively easy to determine the occupation of the questioner from his or her E-mail address or organization name. The various categories selected and number of questions are shown in Figure 2. Figure 2 | Occupation of questioner

The largest group was in the designer/ consultant category. Small, medium, and large organizations were represented, but it is likely that the smaller organizations predominated.

Within the manufacturers/representatives category, most appeared to be from representatives, as opposed to primary manufacturers of geosynthetics. This was clear from the nature of the questions on many occasions.

It was revealing to see many good questions coming from regulators/governmental agencies. Installers/contractors questions were not uncommon, with several having a request to answer the questions quickly! Facility owners were represented by usually “weighty” questions, often of a durability nature. The “other” category included college faculty members and students, as well as financial firms inquiring about trends in the industry.

Type of geosynthetic

It should come as no surprise that geomembrane (GM) and geotextile (GT) questions were by far the most common (Figure 3). Figure 3 | Type of geosynthetic involved The general geosynthetics (GS) group included many questions regarding information on polymers, additives, manufacturing, and applications. Questions on geogrids (GG) and geonets/ geocomposites (GN/GC) were almost all specific and addressed common issues about these geosynthetic materials.

Conversely, the questions on geosynthetic clay liners (GCLs) and geoerosion control materials (GECM) were usually broad and encompassing. There were few questions on geopipe (GP), which was somewhat surprising. In the “geo-other” (GO) category were fibers (both polymeric and natural), geofoam, and geocells.

General category of questions

The largest category of questions focused on information, either specific or general, and often involving specifications (Figure 4). Figure 4 | General category of question This was followed in frequency by specific questions on lifetime (e.g., durability, chemical resistance, and lifetime predictions—both covered and exposed; and on strength (e.g., tensile, compressive, shear and connections). As seen in Figure 4, clogging questions were common (usually geotextiles, but also geonets and drainage composites), as were seaming (including thermal, chemical, adhesive, sewing, and mechanical) and installation questions (including hot and cold weather, handling, equipment | GMA Techline | on geosynthetics, waves/wrinkles, wind issues, and even seagull avoidance). The “other” category includes questions on resins, additives, manufacturing, market size, rate of growth, future trends, and new products.

Difficulty level of questions

Of course, to assess the difficulty of a particular question is extremely subjective. That said, an attempt has been made (Figure 5), with “1” the most difficult and “5” the easiest. Figure 5 | Difficulty level of questions

Note that the trend is shifting slightly toward easier questions, but the 1s and 2s are still quite formidable. In fact, the 14 1s were so meaty that an answer was either completely unknown or would require a special research project to discover a response. As such, we have included all 14 of the 1s (“most difficult,” at least to us) questions.

Perhaps readers have some responses to these questions.

Level 1, question 1

I have a customer interested in the effects of low-level radiation on PVC. So far, a Web search and visit to the PVC Institute Web site failed to turn up any information. Do you know of any papers written on this subject? I recall a paper or two from the mid-1990s on HDPE containment of low-level radioactive material but cannot recall the conference. Better yet, any questions on how to go about determining the effects of gamma and beta radiation on PVC?

Level 1, question 2

Our company specializes in the design of lightweight veneer landscapes for roofs (aka, green roofs). One of our strategies for irrigating thin green roofs is to place a dense fabric at the base of the profile. Water is delivered to the fabric at sparsely distributed locations (e.g., via drip lines or bubblers). We rely on the fabric to distribute the moisture and to mitigate the effects of surface irregularities.

We have tested many products in bench scale, by simply suspending the fabric vertically in a pan of water. Do you have research results on this application or have a preferred test method available?

Level 1, question 3

Please advise on the following:

  • What are the applications for antimicrobials used with biologically active surfaces?
  • What is the antimicrobial consumption by application?
  • What are the antimicrobial distribution channels?
  • What is the antimicrobial gross margin analysis?
  • What is the antimicrobial pricing for biologically active surfaces by application?
  • What is the cost of using antimicrobial by applications?
  • What are the application methods for antimicrobials?
  • What are the leading antimicrobials used?
  • Who are the leading biocide manufacturers?
  • Who are the leading biocide suppliers?
  • Who are the leading masterbatch producers?
  • Who are the leading polymer producers?
  • What is the decision-making process in selecting antimicrobials?
  • What is the ideal antimicrobial?
  • What are the results of market research in this area?
  • What are the regulations for antimicrobials?

Level 1, question 4

I’m trying to see if there is a visqueen type of sheeting available on the market that will be a moisture barrier for a short term (3 to 6 months) before decomposing in the ground, thereby avoiding having to dig it up or otherwise collect it all for disposal. This would be for a soil remediation project covering about an acre.

Level 1, question 5

We are an environmental consulting firm and are looking for any literature or information on studies conducted on the effects of radiation (radioactivity) on HDPE geomembrane systems. I have done searches on the Internet and not been able to find a lot of information. I was wondering if you might know of any sources out there with such information.

Level 1, question 6

For HDPE geomembranes, I am looking for information on what effect there might be, if any, on the integrity of a fusion weld when an extrusion weld is placed directly on top of it. This condition exists when completing patches at T-intersections but there may be an occasion when an additional section liner has to be welded directly on top of a fusion weld for a greater distance. Does the reheating of the fusion seam area caused by the extrusion weld cause any deterioration in the fusion weld? If so, to what extent?

Level 1, question 7

I am in the process of evaluating the mass flux of gas moving through a 30mil PVC geomembrane. I am working with volatile organic compounds in soils. What I need are typical values based on unsaturated soil vapors. I have found information on aqueous liquids but not on unsaturated soil vapors.

I would like to ask if you can provide me with any assistance in finding typical gas diffusion coefficients through geomembranes and/or contacts or references where I can find them.

Level 1, question 8

I’m a geotechnical engineer practicing in Southern California. Recently, we have seen other geotechnical consultants in this area specifying shallow geogrid reinforced compacted fill sections as a means for mitigating surface manifestation of a liquefaction occurrence.

We’re currently evaluating a project where the potential for liquefaction is an issue. Do you have any technical documents/guidelines or research references that could be used to design a geogrid reinforced fill section to address liquefaction?

Level 1, question 9

I am requesting to know if you may be able to provide technical assistance on the installation of pipe through 60mil geomembrane. The geomembrane is installed as a liner to prevent the formation of sinkholes in a very sensitive karst region. We are requiring any potential joint created between the pipe and geomembrane to be 100% sealed for the life of geomembranes.

Level 1, question 10

I am involved in a project to design a geomembrane cover for a waste storage pond located in the northwestern U.S. The cover will need to collect gas that is produced from the pond for the purpose of odor control. In our location, high winds and cold temperatures are a concern. Do you have guidance for addressing these issues? I am especially concerned with the effect wind will have on the liner as 90+ mph wind gusts do occur. Is there design protocol to account for this? And/or, do you have recommendations or suggestions for liner styles or characteristics that are most effective in sustaining high, long duration wind forces?

Level 1, question 11

I received the attached conceptual designs for containment of a battery recycling operation where they propose to “man handle” batteries above the floor surface at this facility.

The operation, as I understand it, is that the batteries are dumped on the floor where piles will be as high as 15 feet, and then they are loaded for further processing by heavy equipment into the recycling operation. It is not intentional to have battery acid drained during this operation but it does, in fact, happen. What type of geomembrane is best suited for this application?

Level 1, question 12

A contractor is proposing installation of a PVC geocomposite in a tunnel as a lining. The California Code of Regulations stipulates the non-use of materials with a flash point of 100°F or less. Would any of the cements/sealers used in installation have a flash point of 100° or less?

Level 1, question 13

We have been asked to study a special case of soil improvement under some 10 stations (totaling about 3 hectares) of a subway line; cross section of a part is attached. As you may note in the attached log, preventing liquefaction is a must. This is also mentioned in their request to us:

From 12m depth, we have a high seismic potential silt and sandstone

Ahvaz can be categorized in medium earthquake risk, P.G.A. = 0.25

The area moisture content is drop down from -9.5 (22.5 to 17.5)

Factor of safety for liquefaction is 0.4in. – 20.7m (it can be so dangerous)

Average F.S. = 0.6, anyway liquefaction can be potential problem

The problem is that we cannot make any vibration due to problems that may happen to adjacent buildings. So the contractor is looking for any innovative improvement methods that don’t need vibration and also is less costly and more rapid than the conventional cement grouting methods available here.

Level 1, question 14

Attached photos are of a multilayered expansion joint, the outer layer photos show cracking in the EPDM outer layer and I would like to have your opinion on the crack mechanism. The joint is exposed to direct sunlight where temperatures can reach 122°F in the shade. This joint has been in service for 3 years or so and has some stress due to lateral misalignment of the mating flanges.

To me it looks like UV damage but I believe EPDM is not prone to damage from this route. Could it be misalignment stresses alone or a mixture of the U.V. and mechanical stress?

Is this cracking atypical for EPDM? How is this likely to progress with time?

Summary and commentary

This article has attempted to let the readers know of the GMA Techline’s existence and some of the demographics and questions involved to date. A venture such as the worldwide solicitation of geosynthetic questions is bound to result in a fantastic array of inquiries, which has indeed happened. We have tried to be impartial and accurate in our answers and if this is not the case, please advise accordingly. Attempts will be made to correct the situation, even as far as correcting answers that may have had an unrecognized bias. However, the overall goal of providing the correct information regarding geosynthetics has been achieved to date. We look forward to the ongoing use of this service.

Robert M. Koerner, Ph.D., P.E., NAE, Andrew Aho is the managing director of the Geosynthetics Materials Association (GMA);

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