PVC Geomembrane Case Study - 25 Years Later

 

NOVEMBER 1993

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The PVC Geomembrane Institute (PGI) is working toward the advancement of the use of PVC geomembranes in appropriate applications. One of the things the Institute is involved in is providing information on topics of interest to our readers. This issue of the Geomembrane Technical Bulletin contains two articles that address some commonly asked questions about PVC geomembranes - durability and plasticizer loss. The first article written by James A. McKelvey, III, an Associate Geotechnical Engineer with Roy F. Weston, Incorporated, takes an in-depth look at the loss of plasticizer and its effects on PVC geomembranes. The second article, 'PVC Geomembrane Case Study 25

"Years Later", found on page 5 discusses the physical properties and serviceability of the material after 25 years in the ground.

We hope you enjoy reading the Geomembrane Technical Bulletin. Any suggestions or comments you may have are welcome.

PGI is continually looking for stories and case histories about your experiences
with PVC liners. If you have one you would like to share, please contact us.

Laurie L. Honnigford
Executive Director, PGI
 

Industry News

Jack Haynes recently reported that the Bureau of Reclamation Canal Lining Demonstration project has been constructed and the ten-year monitoring period has begun. The Bureau has written a report about the specifics of this project. To get a copy contact: Mr. Jack Haynes U.S. Bureau of Reclamation, 1 150 North Curtis Road, Boise, ID 83706-1234. Telephone: 208-378-5093, Fax: 208-378-5066.
 

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PVC Geomembrane Case Study- 25 Years Later

By: David Lauwers
 

Case studies of geomembranes under actual conditions contain some of the most important information that can be gathered to determine long term performance. Opportunities to evaluate the performance of the geomembrane under these conditions are limited because of the expense of excavating the geomembrane and the fear of disturbing the geomembrane in an attempt to obtain a sample. This leaves only limited opportunities, such as when sites are being expanded or require modifications.

In this case study, the opportunity presented itself in the spring of 1993, when a golf course pond was being enlarged and the existing PVC geomembrane was excavated in the process. The site was at the Lake of the North Golf Course located in the northern part of the lower peninsula of Michigan. According to Jerry Matthews, the golf course architect who originally design the project, the PVC geomembrane was installed in the summer of 1968, almost 25 years ago. The material, a 10 mil PVC geomembrane was originally covered by twelve inches of sand. Approximately six to eight inches of silt had accumulated over the sand during this 25 year period. The pond was designed for irrigation and asthetic purposes and to provide duffers with a means to determine if their golf balls would float.

The conditions in this area of the country provide a good testing ground. The winters are cold, with temperatures falling well below 0°F and rising to 90°F at times during the summer. Also based upon some other previous studies of plasticizer extraction, the rainwater may be more severe than a typical municipal landfill leachate. This phenomenon is due to the fact that there is a larger gradient for plasticizer migration in water than leachate, due to the lack of organic compounds in the water. Lastly, this geomembrane was only 10 mil material.

The changes to the geomembrane would occur more quickly with this gauge than the thicker gauges, 20 to 40 mils, that are typically used on large projects today. For all these reasons, this site provided some very meaningful information relating to the long term performance of PVC geomembranes.

Enough samples were taken to evaluate not only the physical properties of the parent material but also the factory and field seams. All seams were made using a chemical fusion weld. Physical testing according to NSF Standard 54 for PVC geomembrane was conducted, along with chemical analysis of the film. The specific tests that were conducted included thickness, specific gravity, tensile, elongation, 100% modulus and tear resistance. Peel and shear tests were conducted on both the factory and field seams.

Test results are summarized in Tables 1 and 2, and Graphs 1 and 2. There are several things which are immediately apparent from this data.

1.  The physical properties still exceed the requirement of NSF Standard 54-83 even after 25 years. In fact they exceeded the NSF 54 Standard by a large margin.

2.  There is no deterioration of the seams by the peel and shear values in either the field of factory seams. All the peel tests of the factory and field seams resulted in film tearing bond.
 

The analytical results confirm that the makeup of this PVC geomembrane has changed very little over the 25 year period. Although an unexposed sample of this geomembrane was not available, if compared against current geomembrane formulas, the plasticizer content has only changed by 12%. Existing PVC geomembrane formulas have about 30% plasticizer, versus the 27.8% found in this geomembrane. The geomembrane had reached a steady state with the surrounding environment and it was not losing any additional plasticizer.

The samples themselves were still very flexible with no sign of deterioration or cracking of the surface. There appeared to be no physical signs that would indicate that the geomembrane had not functioned as designed for the 25 years it was in service. This study only adds to the growing amount of information that indeed PVC geomembranes are a logical choice for a wide range of applications. The fact that they do contain plasticizer is not the Achilles heel as some people would believe, but gives the geomembrane the flexibility that is so important in geosynthetic design, and when properly formulated, provides the permanence to perform in the long haul.

GRAPH 1

TABLE 1

PROPERTY	TEST METHOD	NSF-54-83	25 YEAR OLD PVC
Thickness – measured	ASTM D1593	9.3	9.2
Spicific Gravity	ASTM D792	1.2	1.3
Tensile ppl – MD	ASTM D882	23	31.3
Tensile ppl – TD	ASTM D882	23	29.4
Elongation at Break - TD	ASTM D882	250%	251%
Elongation at Break - MD	ASTM D882	250%	297%
100% Modulus ppi – MD	ASTM D882	9	24.4
100% Modulus ppi – TD	ASTM D882	9	21.3
Tear Reisstance LBS - MD	ASTM D1004	3	5.6
Tear Reisstance LBS - MD	ASTM D1004	3	5.6

 

GRAPH 2 

TABLE 2. SEAM STRENGTH TESTING

PROPERTY	TEST METHOD	NSF-54-83	FACTORY SEAM	FIELD SEAM
Peel Adhesion Lbs	ASTM D413	10	14.73	1.84
Bonded Seam Strength PPI	ASTM D3080	18.4	25.32	28.68

 

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