Technical Paper by D.J. Elton and I. Peggs - IGS - International ...

Technical Paper by D.J. Elton and I. Peggs 

GEOMEMBRANE RESEARCH NEEDS 

ABSTRACT: A US National Science Foundation/Auburn University Workshop was 

held in Summer 2000 to identify geomembrane-related topics that require research. 

Three publications were produced: a geomembrane state-of-practice paper, a paper on 

research needs, and a final paper on organizing similar workshops. The present paper 

focuses on geomembrane research needs, with the intent of moving the profession forward 

by identifying what new knowledge/research is needed and how to get it. Stimulating 

discussion on the subject is a secondary purpose of the paper. Ten professionals, 

selected for their expertise and experience, attended the Workshop. Most facets of the 

geomembrane/waste disposal industry were represented. The participants almost exclusively 

represented United States geomembrane practice. Most of the discussions related 

to high-density polyethylene, linear low-density polyethylene, polyvinyl chloride, and 

polypropylene geomembranes. The Workshop considered seventeen topics related to 

geomembranes in waste, water, and product containment systems. The topics were seam 

tests, seam strength, wrinkles, lifetime predictions, seams types, geomembranes on 

steep walls, thermal seams in PVC geomembranes, geomembranes in bioreactors, durability, 

remote leak repair, defect significance, shear displacements, seams in different 

geomembrane types, leak location and significance, puncture protection, and multiaxial 

testing. 

KEYWORDS: Geomembrane, Research, Liner, Landfill. 

AUTHORS: D.J. Elton, Associate Professor, Civil Engineering Department, Auburn 

University, Alabama, 36849, USA, Tel: 1/334-844-6285, Fax: 1/334-844-6290, E- 

mail: elton@eng.auburn.edu; and I. Peggs, President, I-Corp International, 6072 N. 

Ocean Blvd, Ocean Ridge, Florida 33435-5210, USA, Tel: 1/561-369-0795, Fax: 1/ 

561-369-0895, E-mail: Geoicorp@aol.com. 

PUBLICATION: Geosynthetics International is published by the Industrial Fabrics 

Association International, 1801 County Road B West, Roseville, Minnesota 55113- 

4061, USA, Telephone: 1/612-222-2508, Telefax: 1/612-631-9334. Geosynthetics 

International is registered under ISSN 1072-6349. 

DATE: Original manuscript submitted 7 March 2002, revised version received and 

accepted 12 November 2002. Discussion open until 1 May 2003. 

REFERENCE: Elton, D.J. and Peggs, I., 2002, “Geomembrane Research Needs”, 

Geosynthetics International, Vol. 9, No. 3, pp. 283-300. 

GEOSYNTHETICS INTERNATIONAL • 2002, VOL. 9, NO. 3 283

ELTON AND PEGGS • Geomembrane Research Needs 

1 INTRODUCTION 

A geomembrane research needs workshop was sponsored by the Civil and Mechanical 

Systems Division of the US National Science Foundation and Auburn University in 

the summer of 2000. Ten professionals met for two days and discussed 17 topics 

related to geomembrane research during moderated sessions. The discussion results 

were submitted to the US National Science Foundation. 

Not all possible topics were discussed, due to time limitations. Selection of the topics 

was made jointly by the participants and the organizers. An initial set of topics for 

discussion was proposed in a state-of-practice paper. Subsequently, topics were solicited 

from the participants together with their ranking of each topic’s significance. The 

organizers prioritized the responses in two different ways to arrive at the final topics. 

Although attendees were given the opportunity to modify the topic list at the opening 

of the Workshop, no changes were made. 

Not all attendees agreed with all the suggestions presented in this paper. 

2 ATTENDEES 

Ten professionals were invited, based on their expertise, experience, and availability. 

The intention was to have all facets of the geomembrane/waste disposal industry represented. 

The participants almost exclusively represented United States practice in the 

use of geomembranes. 

Most of the discussions related to high-density polyethylene (HDPE), polyvinyl 

chloride (PVC), and polypropylene (PP) geomembranes. These are the most commonly 

used geomembrane polymers and the ones the participants were most familiar with. 

3 RESEARCH TOPICS 

Seventeen geomembrane topics were discussed. 

1. Avoidance of destructive seam tests. 

2. Significance of strength in seam tests. 

3. Dealing with wrinkles. 

4. Lifetime predictions. 

5. Chemical versus thermal seams. 

6. Geomembranes on steep walls. 

7. Thermal seams in PVC geomembranes 

8. Geomembranes in bioreactors (also known as “active landfill management”, or 

“wet cell operations”). 

9. Durability of textured geomembranes. 

10. Remote repair methods. 

11. Critical defect significance and determination. 

12. Shear displacements - laboratory versus field. 

284 GEOSYNTHETICS INTERNATIONAL • 2002, VOL. 9, NO. 3


13. LLDPE-HDPE and white-black geomembrane welding. 

14. Electrical and other methods of leak location. 

15. Assessing puncture protection of geomembranes. 

16. Significance of leak location methods in light of low leak-rate findings. 

17. Multi-axial testing. 

Each topic is given below, followed by research needs and closing notes for the 

topic. The topics are not arranged in order, nor are the ideas for research listed under 

each topic. 

4 TOPICS DETAILS 

4.1 Topic 1: Avoiding Seam Destructive Tests 

The current state of practice for installing geomembrane landfill liners includes a construction 

quality assurance (CQA) program. “Destructive seam testing” is the part of 

the construction quality assurance program where a sample of an installed geomembrane 

seam is cut out of the geomembrane and tested for mechanical properties. The 

resulting hole is then patched. 

Cutting and patching a hole in the geomembrane seam may lead to increased leakage 

in the liner, especially when the repair seaming method (often extrusion welding) 

is inferior to the original seaming method (often double-track hot wedge welding). 

Removing and patching may also reduce the strength of the seam or create a location 

for failure to initiate. 

It is desirable to avoid this procedure and replace it with a method(s) that does not 

damage the geomembrane yet provides at least the same assurance that the seam is satisfactory, 

both in impermeability and durability. 

Ideas for research in this area include: 

(a) Deliberately create defective double-track, hot-wedge welded seams and inflate the 

air channel to assess the effect of the defect. Then, measure the strength of the 

defective seams and determine the allowable strength based on these results. 

(b) Develop a correlation between non-destructive and destructive test results. 

(c) Develop a better non-destructive seam test. The test should measure the strength 

and integrity of the seam without removing a part of it. Types of non-destructive 

tests used in other fields should be investigated. Non-contact methods can be 

explored involving detection techniques from the aerospace industry. 

(d) Evaluate the effect of channel air pressure on the seam test results. Some countries 

use a higher pressure than the United States. There appears to be a need to standardize 

the pressure used. Investigate testing seam strength with air pressure, nondestructively. 

(e) Develop a statistical method for seam test-location selection. Some industries use 

statistical sampling, instead of relying on the CQA inspector. This may lead to 

more consistency in testing, but may provide an optimistic perspective of seam 



quality. 

(f) Investigate the effect of air channel width in seam testing. Some machines produce 

different channel widths than others. “Squeeze-out” influences the channel width 

in all machines. 

(g) Seek to have objective seam strength data published. There are firms or professional 

organizations that have this data, but have not published it for widespread 

use. Standardized reporting is needed. 

Closing Notes. The following are the several proposed changes in current procedures 

that bear investigation: use of a statistical method to decide where to do a destructive 

test; elimination of sampling at “every 150 m (500 foot)” interval from specifications; 

remove the requirement that thicker geomembranes must have a higher seam strength 

(reduce it to a design strength requirement); and reduce the number of destructive 

seam tests in double-track, hot-wedge welds (and/or test only at suspect locations). 

4.2 Topic 2: Significance of Strength in Seam Tests 

Currently, geomembrane seams are expected to have at least the same strength as the 

geomembrane. This may not be necessary for adequate design, as the geomembrane 

may have much more strength than is needed to function properly. For example, sometimes 

the geomembrane strength is chosen to assist with installation survivability or 

weldability. This strength may exceed that required for engineering stability. 

Strength testing of geomembrane seams may not be generating useful information 

on seam bond strength; rather it reflects the low cross-sectional area of the geomembrane 

tab compared to the relatively high bonded area. If the bond efficiency exceeds 

only approximately 15%, the geomembrane will break, in both shear and peel tests, 

before the seam bond is adequately challenged. 


(a) Determining what bond (seam) strength is acceptable based on design criteria 

rather than the currently required 90% of the geomembrane strength to be in the 

seam. If the designer only needs a certain tensile strength, perhaps seams should 

only be tested to insure that strength. 

(b) Shear strength the geomembrane parallel to the seam may be more important than 

strength perpendicular to the seam. 

(c) Stress versus strain data for the geomembrane adjacent to the seam, which is the 

weakest part of the installed geomembrane system, is needed. Perhaps place a 

clamp on the seam and a clamp on the geomembrane and then pull apart. 

(d) How to make stress versus strain properties of a weld the same as parent sheet? 

(e) What is the minimum strain acceptable to determine a good or bad seam? 

(f) What parameters define a “good” seam? Are bond and peel strengths needed? 

Bond efficiency (seam strength versus material strength)? Shear elongation and 

peel separation? Determine data needed to define a good seam: what is needed and 

at what level (workmanship?). 



Closing notes. Most leaks in the geomembrane are found away from the seams. 

Experience shows that in-service seam failures are uncommon. Electrical leak detection 

has shown that most geomembrane damage results from placement of the protective 

cover/drainage layer. More effort needs to be spent on leaks away from the seams. 

Construction quality can be improved with the publication of a “Manual of Installation 

Practice”. 

4.3 Topic 3: Dealing with Geomembrane Wrinkles 

Wrinkles occur in a geomembrane during installation due to changes in liner temperature 

and deployment of cover soil. The wrinkles may interfere with leachate handling, 

increase the infiltration beneath a geomembrane (lack of intimate contact between the 

geomembrane and clay beneath), decrease durability, and increase the chance of construction 

damage. While current specifications often require “no wrinkles”, a more 

measurable/enforceable description is needed, as well as a greater understanding of the 

effects of wrinkles on landfill liner performance. Wrinkles occur on almost all 

geomembrane liner projects in North America. There is no clear guidance on what 

constitutes an acceptable amount of wrinkling for a given installation. There are often 

opposing goals in avoiding wrinkles and avoiding “bridging” or “trampolining”. On 

uncovered slopes, wrinkles will travel down slopes and cannot be redistributed up 

slopes. 

Current wrinkle reduction techniques include: 

• Coordinating installation and covering temperatures. For example, deploying the 

geomembrane during the warmer part of the day and covering during the cooler 

part of the day (especially night time). 

• Using light-colored pigments on the surface of the geomembrane instead of the traditional 

black. 

• Textured geomembranes and more flexible geomembranes tend to have less and/or 

lower amplitude wrinkles. 


(a) How significant are wrinkles? A quantitative study is needed. The effects of size, 

direction, and distribution of wrinkles on performance need investigation. The 

answers will likely depend on the type of installation (e.g., landfill liner, or cover, 

or pond liner) and the type of geomembrane used. 

(b) New construction procedures for “wrinkle-free” geomembrane installation need 

investigation. The Germans limit time of day of geomembrane installation and 

slightly pretension geomembranes to eliminate wrinkles at the time of cover soil 

placement. The application of ballast tubes on slopes during installation may 

change the direction of wrinkles on the slopes. 

(c) An evaluation of the cost or risk versus the benefit of avoiding wrinkles needs to be 

performed. Obviously, the German model of the “wrinkle-free” installation would 

be technically desirable. The question of the economic benefit must be considered. 

To date, the geomembrane installation industry has de-facto presumed that the Ger- 



man approach is not economically justifiable. 

Closing notes. More coordination between geomembrane installers and landfill soil 

cover contractors is needed; a “Geomembrane Installation Manual of Practice” is 

needed so that CQA is better (recommendations in the manual need to be borne out by 

research). The Manual would provide much needed guidance for landfill construction 

practices to determine what level of wrinkling might be acceptable for different types 

of projects that use different types of geomembranes and would provide suggested 

construction techniques that could be used to realistically achieve those goals. 

4.4 Topic 4: Lifetime Predictions 

Geomembrane lifetime predictions are needed. The tools for making predictions of the 

life of polymers are better than ever. The current oxidative induction test (OIT) may 

not be a very good indicator of lifetime. The water vapor transmission (WVT) test may 

not define resistance to chemical breakdown of geomembranes. Damaging flaws and 

defects need to be identified, and their critical sizes in different applications defined. 


(a) A definition of “lifetime” is needed. Is this a change in a material property or performance? 

For example, some solvents may weaken a geomembrane, but never 

cause a breach. 

(b) The OIT alone is not a good indicator of durability. A better interpretation of the 

results of this test is needed vis a vis lifetime prediction. Moreover, currently, there 

is a wide variation of OIT results between laboratories. 

(c) The results of OIT on geomembranes with the new (2000) anti-oxidants need interpretation. 

Some antioxidants may not give high OIT values but may provide good 

service. 

(d) An examination of OIT versus xenon-arc tests is needed, to determine the applicability 

of each, and how to compare the results of each. OIT evaluates resistance to 

oxidation; xenon arc evaluates resistance to oxidation, ultraviolet radiation, and 

moisture. 

(e) Perform an investigation to determine if there is a relation between WVT and 

chemical resistance characteristics of a geomembrane. 

(f) Investigation of the durability of new plasticizers is needed. Perhaps newer ones 

can also provide greater geomembrane lifetimes. 

(g) Evaluate how OIT changes in surface layers and through the body of the material 

influence material mechanical durability. 

Closing notes. None of the current geomembranes fail the ASTM D5747 chemical 

resistance test; a paper on the lifetime predictions for HDPE and PVC is needed; an 

OIT state-of-the-art paper is needed. 



4.5 Topics 5: Chemical versus Thermal Seams 

There are two major types of geomembrane seams – chemical and thermal seams. 

Both can provide adequate assurance against leaks. Selection is often based on the 

geomembrane material. Thermal seams include hot air welding, extrusion of melted 

polymer, and single-track and dual-track wedge welding. The advantages and applicability 

of chemical and thermal seams need further investigation. Peel-test criteria are 

different for chemical and thermal seams – perhaps this is unreasonable. 


(a) Are chemical seams as good as thermal seams (or is one significantly better than 

the other)? It is harder to perform construction quality control/construction quality 

assurance (CQC/CQA) on chemical seams. An investigation of the quality of each 

installed seam type is needed. 

(b) What acceptance criteria should be adopted for each type of seam? Should they be 

the same? Is the peel test appropriate for each? Should a different interpretation of 

the peel test be applied to each? 

(c) Improved thermal welding for PVC geomembranes is needed. Current methods 

may cause loss of plasticizer. The use of dual-track welders, which allow air channel 

pressurization to check for leaks, is desirable. However, the heat from them 

may compromise long-term performance. More investigation of procedures for use 

of “mini-wedge” welders on PVC is needed. Minimum PVC geomembrane thickness 

for thermal welding is needed. 

(d) Are there better ways of making chemical seams? 

4.6 Topic 6: Geomembranes on Steep Walls 

Abandoned quarries with steep, even vertical walls are beginning to be used for landfills. 

This provides new design challenges. Quarry walls are often rugged and have texture 

sizes ranging from gravels to boulders. Therefore, the concept of cushioning needs 

to be a bit larger to encompass the need to create an acceptably smooth surface by filling 

voids that might not cause puncture, but lead to membrane bursting. The designer 

will have to deal with macroscopic undulations in addition to the smaller, localized 

protrusions that may cause puncture. Hence, protection here includes micro- and 

macro-puncture and reinforced veneer facings. 

These large open areas present special problems, particularly with lining and drainage 

systems. The installation of geomembranes on the steep slopes requires research. 

Such facilities are being developed in Southeast Asia, California, Virginia, the United 

Kingdom, and elsewhere. Lining systems and their installation require research. 


(a) What protection can be used to keep the geomembrane from being punctured by 

the sides? Can protective layers be hung from the top of the wall? Perhaps geofoam, 

spray-on impervious or pervious cushions, tires or tire chips, or spray-on 

geomembranes can be used. 

(b) There are problems monitoring deep quarry sites for leakage. The extreme depth, 



and occasionally depth below the water table, present special design challenges. 

New monitoring techniques are needed that allow adequate access to the quarry 

floor for monitoring. Perhaps a new class of remote leakage sensors is needed. 

(c) The stresses on geomembranes in the direction of the seam (not perpendicular) 

may be much greater than for conventional installations. Research on the longitudinal 

strength of seams is needed. 

(d) Need for double liner systems on vertical walls needs investigation. They may not 

be necessary. 

(e) Downdrag on lining systems needs investigation. Large waste settlements are 

expected. The effects of these settlements on the lining systems may be disastrous. 

New ways of reducing downdrag (slippery coatings, delaminating geomembranes) 

need to be developed and evaluated. Stronger geomembrane anchorages may have 

to be developed. 

Closing note. Quarry (or similar) lining is a small, but an increasing part of the 

geomembrane industry. 

4.7 Topic 7: Thermal Seams in PVC Geomembranes 

Thermal seaming of PVC geomembranes is becoming more popular. The effect of 

using heat on the long-term properties of PVC geomembranes is not well known. The 

effect of thickness on heat-related changes is not known. While it is known that heat 

drives off plasticizers, the effects of reduced plasticizers on seams are not well known. 


(a) The effect of heat on PVC geomembranes in and immediately adjacent to seams. 

PVC geomembranes use plasticizers more than other polymeric membranes. The 

heat used for seaming may drive off the plasticizer, changing the quality of the 

seams. This is becoming more of a concern because new plasticizers are not subjected 

to as thorough testing as older plasticizers. 

(b) The development of plasticizers that are more heat resistant is needed to improve 

thermal welding. 

4.8 Topic 8: Geomembranes in Bioreactor Landfills (also known as “Active 

Landfill Management” or “Wet Cell Operation”) 

The use of landfills as bioreactors is gaining momentum. In a bioreactor, liquids are 

added to the waste to expedite decomposition. The expedited decomposition increases 

the landfill gas production, landfill temperatures, and rate of waste settlement. Landfill 

temperatures as high as 80°C have been measured. The elevated service temperatures 

could impact the performance of the geomembrane. 


(a) High concentrations of landfill gas can show up between double liners. Research is 

required to determine if diffusion (rather than leakage) through geomembranes can 

create this problem. 



(b) Bioreactors have high temperatures. Temperature monitoring of geomembranes 

and subgrades in bioreactor landfills is needed. 

(c) Increased temperature effects on geomembranes bear investigation, as well as the 

effect of cooling when bioreaction is done. What geomembrane properties change 

and how could they impact the performance of the liner system? Thermal expansion, 

stress cracking resistance, puncture resistance, strain related creep, oxidation 

resistance, and stress relaxation may change significantly with heating and cooling. 

(d) The effect of large temperature and large thermal gradient up the sides of the landfill 

as hot gases escape needs investigation. Large thermal gradients may cause, for 

example, large differential expansion of the lining systems. 

4.9 Topic 9: Durability of Textured Geomembranes 

Textured geomembranes are used to improve landfill stability and stability of liner systems. 

Stability issues include interim filling of cells (short-term stability) or final landfill 

configurations of canyon fills (long-term stability). The short-term durability of 

textured geomembranes, due to construction stresses, has been investigated. However, 

the long-term performance of frictional properties of the geomembrane has not been 

investigated. Chemical degradation, strain-related creep, or elevated temperature are 

potential factors to consider. 


(a) Evaluation of the frictional properties of the delivered material is needed. Asperity 

height provides a qualitative evaluation, but doesn’t confirm design assumptions. A 

quick conformance friction test in the field that includes an ability to assess temperature 

effects is needed. German practice may be a good starting point for this 

research. 

(b) Unavoidable field abuse of geomembranes during construction may damage texture. 

A test/procedure that simulates field abuse would be useful. Texture evaluation 

research at Georgia Tech University (Atlanta, Georgia, USA) may be a good 

starting point for developing a field evaluation. Data from existing applications are 

needed, as well as experimental evaluations. 

(c) If sprayed-on texture is removed (delaminates), does it leave depressions/defects 

on the geomembrane that may lead to leakage due to changes in the geomembrane 

makeup or decreased thickness? 

(d) Does the angular nature of texture cause stress concentrations, leading to cracks or 

reduced durability? Does the bonding method for spray-on texturing affect stress 

cracking resistance? 

(e) Long-term creep tests on textured sheet are needed. This may help designers understand 

if there will be a reduction in the friction properties of textured sheet. The 

effect of resin type on texture durability is needed. 

(f) A comprehensive evaluation of friction change with exposure to various chemicals 

is needed. 



4.10 Topic 10: Remote Repair Methods 

When flaws are found in seams, and leaks are found in lining systems, they must be 

repaired. At present, except for the concept of a geosynthetic clay liner, this requires 

exposing the liner, cleaning it, and making repairs using conventional installation 

technology. 

Repairs on seams and on the liner during construction can be made relatively easily. 

However, when the liner has been covered, especially with a significant depth of waste, 

repairing is very difficult. Failure to repair may result in premature landfill closure. 

Electrofusion technology has been promoted, which is claimed to be effective 

underwater, but has proven to be marginally effective. After a hiatus of a number of 

years, electrofusion technology is now being reinvestigated and further developed. In 

Japan, precise drilling and injection grouting has been attempted to repair leaks, 

although this approach offers the potential for further damaging the liner. The emphasis 

must be to develop remote repair methods. Problems would include locating the 

leak, developing a material that would seal the leak in adverse conditions (heat, pressure, 

chemical, and moisture), being cost-effective, and providing proof that the repair 

was effective. 


(a) Use a bentonite plug, grout, or polyurea to repair the hole in the geomembrane. A 

tool could be inserted through the waste near the liner leak and the material 

injected. Problems would include locating the leak, applying the correct amount of 

a material that would make the seal in adverse conditions, and finding a plug material 

that would not degenerate. 

(b) Develop a method using the electrophoresis of clay to locate and plug the hole in 

the liner. This method uses electricity. The method would have to overcome electrical 

conductivity of some waste components and the chemical make-up of the 

leachate. Laboratory studies indicate this process has potential. 

(c) Develop a clotting agent suspension, which could be applied before the geomembrane 

is covered, or injected into the waste later. Perhaps the suspension would 

begin to leak through the geomembrane when a hole develops, and clot in the hole 

as movement progresses, similar to the way human blood clots. 

(d) Develop chemicals that react with HDPE and PVC. The chemical would have to 

leave the geomembrane intact. The geomembrane polymer could act as a catalyst 

for the reaction while not using large amounts of geomembrane material sufficient 

to threaten geomembrane integrity. 

(e) Develop a technique of underwater (under-leachate) thermal welding. These methods 

could be used in conjunction with excavation of the waste, but not the leachate 

when a leak is located. New polymers and equipment may have to be developed. 

(f) Use of micromachines or nanobots to both locate and repair the leak. The robots 

could be embedded in the geomembrane during manufacture, added during installation, 

or introduced after installation. Robot sensors could detect leaks by thermal 

or hydraulic gradients and move to the leak. The robots could do welding (or other 

repair), or be made of a material that was sacrificial and form the plug themselves. 



(g) Develop a five-layer coextruded geomembrane in which the second and fourth layers 

interact and swell to seal a hole when water/leachate penetrates a hole. 

Closing note. Some European landfills have an inspection gallery under parts of the 

liner system, allowing visual geomembrane leak inspection by humans. 

4.11 Topic 11: Critical Defect Significance and Determination 

Often the problem when making repairs to geomembranes is to determine at what 

point a defect requires repair. For example, when is it necessary to fix a scratch and 

when is acceptable to not fix it? Such knowledge would be very beneficial in terms of 

cost and time relating to making repairs on these defects. Critical defect characterization 

needs to be determined to assess geomembrane lifetime. Critical defect characterization 

will assist the CQA team in identifying defects that need attention. 

Locations in landfills and ponds where geomembrane defects are most likely to 

have a detrimental effect should be identified - for example sumps and the corners of 

big ponds are more critical than central areas. Ponds may be more critical than landfills, 

since the liquid pressure is higher, and more evenly distributed, and the pressure 

does not decrease when the liner settles. Pond liners are often exposed making them 

more susceptible to contraction stresses. 


(a) Develop a classification method for scratches and notch defects including the following 

parameters: shape, length, width, depth, and location of the flaw. Fuzzy 

logic developed in conjunction with expert opinion may be very useful. The significance 

of the defect may depend on the waste type. 

(b) Develop a method, using the above classification, which indicates when to fix a 

defect and when to leave it alone. In addition, determine how many and what kind 

of scratches are cause for rejection of a geomembrane panel. Fuzzy logic is a likely 

source for development of this method. 

(c) More research on the effects of scratches on different polymers, including generation 

of stress cracking in HDPE is needed. Crack initiation and propagation kinetics 

information is needed. Some stress cracking may be mitigated by choice of 

polymer. 

(d) Develop design methods (and procedures) that avoid creating situations that lead to 

defects in installation. A “construction-friendly” design is needed. 

(e) Develop new effective ways to fix defects and flaws and evaluate the fix. For 

example, extruding a bead, fusing, or grinding out the defect without damaging the 

geomembrane or creating additional stress concentrating features. Perhaps the 

addition of a different polymer to the notch is needed. 

(f) Develop new methods to locate defects and flaws in a geomembrane (e.g., spreading 

a coating on the geomembrane, or using a colored dye for detection). There 

may be invisible light optical methods from the aerospace industry that can be 

transported to this industry. 

(g) Determine the effects of tear initiation, and defects like bubbles, dust, and sand in 



the geomembrane, particularly in a seam. The effects of the shape, length, diameter, 

depth of these defects, and their proximity to other defects bears investigation. 

(h) Determine how fast stress relaxation in geomembranes takes place. This abates 

stress cracking in geomembranes and may alleviate the need to fix many flaws, 

speeding installations and reducing costs. 

(i) Identify locations in liners and covers where geomembrane defects are most likely 

to develop into detrimental defects. This may lead to proactive specifications, 

resulting in fewer defects. 

4.12 Topic 12: Shear Displacements - Laboratory Testing versus Field 

Experience 

For large direct shear tests, there is a need for more consistency in lab data and 

improvement of procedures. There is a question of whether a better test than the direct 

shear test is needed or just better education in the use of this data. 

There is also speculation on how well the laboratory direct shear tests represent 

field conditions and how test results relate to the factor of safety used in design. Are 

designers getting good data? 


(a) More detailed investigation of multi-interface (sandwich) testing and interpretation 

of the results. 

(b) Develop more durable, more accurate, and less expensive field instrumentation for 

better measurement of displacements and shear stresses. This is especially needed 

for the different layers of leachate collection systems on landfill side slopes. Moreover, 

data collection as the waste is being placed against the side slopes is needed. 

The data could be used to validate strength and downdrag design assumptions. 

(c) Develop a peak versus post-peak plot of shear displacements. Implement designs 

where post-peak strengths are used on slopes and peak strengths are used on the 

floor of the landfill. 

(d) Develop larger standard shear boxes that can go past 7.5 to 10 cm (3 to 4 inches) 

travel. This is needed because of the potential large displacements from seismic 

events can cause non-damaging displacements up to 30 cm (12 inches). In addition, 

there is a loss of scale from the smaller boxes that does not accurately represent 

field situations. 

(e) Implement better direct shear test training for technicians to get more consistent 

results. Much consistency is lost simply from a lack of test method education. 

(f) Instrumentation is needed to measure how effectively a geomembrane over a geosynthetic 

clay liner keeps moisture from moving through a geosynthetic clay liner, 

reducing interface friction. 

4.13 Topic 13: LLDPE-HDPE and White-Black Geomembrane Welding 

Welding two different geomembrane types together can pose problems. The procedures 

for welding the two types of geomembranes are of concern. There are current 



techniques that are adequate. New techniques, perhaps requiring less skill than current 

techniques, would be useful. For example, in cases when the stiffer material is on the 

bottom side of the overlap, the welder may have incursion into the weld bead. Typically, 

to achieve a better peel test strength, the stiffer material is placed on top. When 

doing an extrusion weld between these types, use the stiffer material as the extrudate. 

There may be ways of avoiding these details. 

Welding old and new sheets requires trial welds. The known problems are related 

to aging of the old liner whereby the aging is not seen on the surface, is oxidized, and 

becomes part of the blend when seaming. The oxidized surface peels off at that location. 

Most of these problems are caused by debris on the geomembrane before welding. 

Techniques for identifying potential welding problems are needed. 

It is not necessary to grind the white surface off a black geomembrane before welding 

it to another geomembrane. 

Currently, there has been little success in thermal welding of PP to HDPE. A new 

method of welding, or improved procedures for existing welding machines, could 

improve the success rate. 


(a) Research the thermal effects at the weld interface of two different geomembrane 

materials. 

(b) Investigate the use of a PP to HDPE transition strip to attach these two geomembrane 

types. Perhaps geomembranes made from a mixture of PE and PP, or a composite 

material would be effective. 

(c) Research the effects of combinations of weld temperature and speed, particularly 

the use of high temperature and low speed. 

Closing notes. The procedure of welding the two types of products has been done for 

several years. The techniques should be placed in the open literature, perhaps as part of 

a manual. Further investigation to develop better techniques is needed. All of the 

above-mentioned research depends on an acceptable definition of a “good” weld, a 

term that is not currently well defined for all situations. 

4.14 Topic 14: Electrical and Other Methods of Leak Location 

Electrical methods of leak detection were introduced circa 1982 for liquid impoundment 

liner leak detection, uncovered liners, and soil and waste-covered liners. 

To use this technique, a reasonably homogenous electrically conductive medium 

must be above the liner and a conductive medium immediately below the liner. This is 

not always the case. The electrical current will often flow through pipe penetrations, 

batten bolts, concrete pads, or soils at the edge of the cell being tested. This extraneous 

flow reduces the sensitivity of leak location. 

Alternatively, a pattern of electrodes can be placed under the liner as it is being 

installed. These systems enable constant monitoring and location of the leak as soon as 

it occurs. More recent technology uses a series of electrodes installed around the circumference 

of a lined facility. Such a system can also be used to locate leaks in a sec- 



ondary liner. 

These methods only locate leaks in liners. They do not identify flaws that may not 

be leaks at the time of testing, such as poor bonding and voids. 


(a) Develop a method to find a defect (e.g., scratch, gouge, or cut) (a potential leak) 

under the “flap” of a double-wedge seam. Welders may score the geomembrane in 

the act of welding creating a weak location that may develop into a leak. Since 

these are not visible, they are not currently detected. 

(b) Acquire a database of causes of leaks in geomembranes, which includes statistics 

on the following: severe holes caused by machinery, punctures by rocks and tools, 

razor slits, extrusion pinholes, and seam failures. The database may help revise regulations, 

standardize CQA, and provide guidance that is currently focused more on 

seam requirements, but perhaps should focus more on the liner itself, where the 

majority of large leaks are usually found. 

(c) Investigate the potential for geonets to be pushed through geomembranes. Manufacturers, 

facility owners, and commercial leak survey firms could provide much of 

this data. 

(d) Expand electrical leak survey techniques such that they may be used in more liner 

configurations. For example, for use on side slopes, especially when there is a geonet 

between the liners. 

(e) Develop a new membrane that finds its own leaks, perhaps using fiber optics or 

other sensing technology. Geomembranes that change properties where the leak 

occurs (e.g., color or sound) would aid in leak detection. 

(f) Compile data on European leak location methods. The United Kingdom has completed 

this. Compare all methods and then do trials of each. For example, the 

under-liner electrodes used in France bear investigation. 

(g) Answer the following questions: Are little leaks worth finding? Below what size? 

Are leaks at welds significant? Are leaks in certain areas of the landfill more critical? 

(h) Improve methods of locating leaks after the waste is placed. Current methods 

involve removal of the waste to detect (or confirm) a leak. This is cost prohibitive. 

(i) Investigate better methods of placing cover over geomembranes, since it appears 

that approximately 73% of the leaks are caused while covering the geomembrane. 

Closing notes. The leaks along welded seams are seldom worth locating because 

they are small compared to the large leaks found between seams; small leaks are seldom 

worth locating because small amounts of leachate goes through them. The most 

severe holes are caused by construction machinery, not inadequate seaming. 

4.15 Topic 15: Assessing Puncture Protection of Geomembranes 

When puncture survivability is of concern, field trials are often performed on a builtup 

cross section of the liner in a small test pad on site. The pad is trafficked by moving 

heavy equipment on the test pad. The geomembrane is exhumed and examined for 



signs of construction damage, including puncturing, and tested for changes in uniaxial 

mechanical strength. 

Interpretation of the results is difficult and incomplete. Typically, no consideration 

is given to the elastic recovery of indentations that occurs when the geomembrane is 

exhumed, nor is any consideration given to the stress cracking resistance of HDPE 

geomembranes (caused by scratches or indentations from traffic) in evaluating the significance 

of any damage. 

Whether or not the geomembrane is punctured at the time of the test is only part of 

the problem. The other is whether the damage that occurs in service will significantly 

shorten the life of the geomembrane. 

There are currently two quasi-performance lab tests to assess the puncture protection 

of geomembranes (both in ASTM D5514), but do these tests accurately represent 

field situations? 


(a) Research the effects of time and temperature on puncture survivability. The current 

quick, room temperature test does not simulate the field conditions. Develop a better 

evaluation of the geomembrane damaged by the test. 

(b) Find a laboratory test that better simulates field performance. For example, press 

real waste on the geomembrane and put the waste on top instead of below the 

geomembrane. Investigate the differences between deforming a geomembrane over 

the puncturing device and driving the puncturing device through a fully supported 

geomembrane. 

4.16 Topic 16: Significance of Leak Location in Light of Low Leak-Rate 

Findings in the Field 

“Leak location” methods are non-destructive methods using electrical resistivity methods 

to find holes anywhere in a landfill geomembrane before waste placement. These 

methods are non-destructive and can be used after soil cover is placed. These are 

advantages over conventional CQA destructive testing, since these methods test the 

entire geomembrane, not just the seams. 

Landfill performance data continues to be collected indicating that composite-lined 

and double-lined landfills with leak detection systems are working as designed, providing 

adequate leachate containment and protection of groundwater resources. With 

this data in hand, should the profession be concerned about the status quo of geomembrane 

installation CQA programs, or should the profession be looking at the data being 

provided from leak location surveys that indicate the status quo CQA programs are 

currently not giving us defect-free geomembrane installations, and pursue a change to 

the status quo to try and improve construction quality? Perhaps electrical resistivity 

leak location on the geomembrane liner installations during and upon completion of 

construction could be the “hammer” to make contractors produce higher-quality workmanship 

for environmental containment systems. 

It would be useful to compile information from leak location surveys and to evaluate 

the information to pinpoint where future research is needed. 




(a) Compile information on leak location testing, including: the cost to perform electrical 

resistivity leak location testing, and subsequent benefits; the limitations of electrical 

resistivity leak location, such as the geomembrane liner configurations where 

leak location testing cannot be performed; and a database of the number of defects 

found, their types, and the type of construction that contributed to the defects. This 

would help improve construction specifications and procedures. 

(b) Develop a criterion for deciding when to require a leak location inspection, as 

opposed to just seam inspection. The criterion would probably be a combination of 

facility function, cost of remediation, seam quality, and number, size and distribution 

of leaks found by conventional methods. Data suggests that leak location is 

more effective than seam inspection in locating leaks and perhaps should be the 

primary form of leak detection. 

Closing notes. Information provided during many construction quality control and 

construction quality assurance (CQC/CQA) training programs in the mid-1980s indicated 

that approximately 70% of all liner defects were a result of liner construction. 

This was the basis and emphasis for proper CQC/CQA procedures being established to 

improve geomembrane installation quality at that time. Nosko et al. (1996) suggest 

97% of defects are construction related. Leak location services hold strong potential to 

compliment status quo seam testing requirements, resulting in more secure containment 

system construction. 

4.17 Topic 17: Multi-Axial Geomembrane Testing 

Multi-axial testing of geomembranes may improve our understanding of the strength 

of geomembranes. Here, a circular panel of geomembrane is inflated until failure. The 

inflated shape is not spherical. 

The test results are in need of better interpretation and refinement. The test results 

are sensitive to the strain rate, the initial conditions, and the frequency of data collected. 

Also, the test results may be useful in predicting the performance of geomembranes 

over compressible foundations (e.g., soft soils and waste). 

The test produces isotropic stress conditions only at the top of the bubble. If the 

hole or defect is at the top, data are easily interpreted. If failure initiates elsewhere, the 

data are difficult to interpret. 


(a) A new interpretation of data having a peak strength is needed. The current multiaxial 

test data reduction does not show this, because it is hidden by the “spherical” 

interpretation of data. 

(b) The current calculated “average” strain is not a good measure of the strain in the 

geomembrane because of the large difference in strains in the bubble. A better 

interpretation of strain is needed. 

(c) The stress conditions are isotropic at the bubble top, but not on the rest of the bubble. 

A better way to interpret the results that accounts for this anisotropy is needed. 



(d) Reviving the “trough” test, which is more two-dimensional and has more plane 

strain conditions. This could help work around the problem of interpreting failures 

in multi-axial testing that do not occur at the top of the multi-axial bubble. 

5 OTHER TOPICS CONSIDERED WORTHY OF RESEARCH 

Other topics that require research are identified below. These were not discussed in 

detail at the Workshop. 

(a) Develop a design procedure that incorporates tear strength of geomembranes, 

which is a common failure mode on side slopes. 

(b) Develop new resins having the required properties (including durability) and the 

ability to interact with other polymers, and are smart materials, that might detect/ 

heal their own leaks and perform better than geosynthetic clay liners. 

(c) Develop better welding techniques that are faster and more reliable than current 

ones. Extrusion welding needs improvement to reduce leaks and increase the welding 

speed. 

(d) Develop an economic, durable geomembrane that “passes gas without passing liquids”, 

for use in bioreactor landfill covers. Concerns about greenhouse gasses 

release and oxidation of the geomembrane would need to be addressed. 

(e) Develop a geomembrane that passes water in only one direction to allow water 

expelled from consolidation of clay under a geomembrane to pass into the landfill 

but not allow leachate to pass out of the landfill. Removal of water beneath the 

geomembrane increases the friction/adhesion beneath the geomembrane, resulting 

in less chances for slippage on side slopes. 

(f) Develop a low water-vapor transmission geomembrane to reduce leachate escape 

from landfills. 

(g) Development of geomembranes more resistant to chemical diffusion. 

6 CONCLUSION 

Much geomembrane research remains to be done. The authors hope that the present 

paper will stimulate geomembrane research and discussion. The anticipated results of 

the present paper are newer, better ways of making, evaluating, and installing 

geomembranes in many applications. 

ACKNOWLEDGEMENT 

The Civil and Mechanical Systems Division of the US National Science Foundation 

and Auburn University funded the Geomembrane State-of-Practice Paper and Vision 

Paper Development Workshop. This support is gratefully acknowledged. 



REFERENCES 

ASTM D 5514, “Standard Test Method for Large Scale Hydrostatic Puncture Testing 

of Geosynthetics”, American Society of Testing and Materials, West Conshohocken, 

Pennsylvania, USA. 

ASTM D 5747, “Standard Practice for Tests to Evaluate the Chemical Resistance of 

Geomembranes to Liquids”, American Society of Testing and Materials, West Conshohocken, 

Pennsylvania, USA. 

Nosko, V., Andrezal, T., Gregor, T., and Ganier, P., 1996, “SENSOR Damage Detection 

System (DDS) – The Unique Geomembrane Testing Method”, Geosynthetics: 

applications, design and construction, de Groot, M.B., den Hoedt, G., and Termaat, 

R.J., Editors, Balkema, Proceedings of the First European Geosynthetics Conference 

EuroGeo1, Maastrict, Netherlands, September 1996, pp. 743-748.

Technical Paper by D.J. Elton and I. Peggs - IGS - International ...

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