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Seaming of geosynthetics
Geotextiles and Geomembranes 9 (1990) 481-485
Seaming of Geosynthetics
Robert E. Landreth United States Environmental Protection Agency, Risk Reduction Engineering Laboratory, Cincinnati, Ohio 45268, USA
ABSTRACT Owners of containment facilities are using geosynthetics at an increased rate. A major concern in their use is the ability to field seam the materials such that the design function of the geosynthetic is transferred through the seam. This paper discusses potential concerns and describes quality assurance techniques that will, when utilized, help ensure that the facility will be constructed according to the design.
INTRODUCTION Field seaming of geosynthetics is probably the most critical of all the functions including design and installation. A great deal of skill is required in making a seam as strong as, as impermeable as, as chemically resistant as, etc., the parent sheet. From a public owner's perspective there should be no difference of any kind anywhere in the geosynthetic material. Since this condition cannot be met, what is the next best result that we can expect?
ISSUES OF C O N C E R N When geosynthetics are discussed they usually include geonets, geotextiles, geogrids, membranes and others. Their design function can be transmissivity or permittivity of liquids and gases, bedding or cushioning, hydraulic barriers or load transfer to mention only a few. The materials 481 Geotextiles and Geornembranes 0266-1144/90/$03.50I~) 1990 Elsevier Science Publishers Ltd, England. Printed in Great Britain
482
Robert E. Landreth
may be designed to act independently or as part of a total system. The designer will consider redundancies where performance is critical. The designer may also include redundancy where he knows that the joining of geosynthetics will be l©ss than perfect. The designer must address a variety of seam types, e.g. sewing of geotextiles, ties or rings for geonets and geogrids, and solvents, heat or others for membranes. He must take into account the site specific conditions such as the weather, foundation preparation, and the ability of the installation crew to install the materials according to the design function. A designer should know what seaming techniques work best for the material he is working with and must have some basis understanding of the limitations. As an example, if he knows that the finished seam characteristics will only represent 80% of the characteristics of the parent material the resultant design will take this into account. If he knows that the material will be placed under adverse environmental and site-specific conditions the d ea~gn will accommodate the concerns. The materials may have to be changed or a more detailed installation plan may have to be developed. Regardless of tile issues raised for a particular site, the designer should have at his disposal the necessary information to properly design and engineer geosynthetics to perform as desired.
CONSTRUCTION QUALITY ASSURANCE (CQA) FOR GEOSNTHETICS The Agency has long recognized that a good quality assurance plan can help bridge the gala between the owner/operator and the installers to obtain a facility that will be as good as or better than the design. Although this plan may be ~latively 0xpensive, many owner/operators will agree with the Agency's ¢iew because they can then be much more confident that the facility will be constructed according to the design. There are at least five elements of the CQA plan that when properly addressed will help ensure quality construction for geosynthetics: (1) responsibility and a~thority, (2) construction quality assurance (CQA) personnel qualifications, (3) inspection activities, (4) seam sampling strategies, and (5).documentation.
ResponslbilRyandauthority Because a geosynthetic may be manufactured by one company, fabricated by another, and installed by a third, various people have responsibilities within the construction process. They can include engineers who generally
Seaming ofgeosyntheacs
483
design the components and prepare specifications, manufacturers who fabricate the geosynthetic, and contractors who perform the installation. The recent growth in the geosynthetics industry makes it necessary to exercise care in selecting firms with proven experience in all aspects of their operation.
CQA personnel qualifications The C Q A officer should be a professional engineer or equivalent with sufficient practical, technical and managerial experience to understan4 H e assumptions made in the design of the facility and the install~ion requirements of the chosen geosynthetic. In order to build on this hard-to-find experience, some firms assign (but do not bill for) an engineer-in-training to work with the trained CQA officer on the job to develop field expertise.
Inspection Inspectors should be aware of the damage and defects geosynthetics can suffer during shipping, storing and placement. For example, highcrystaUinity membrane panels fabricated at the factory rather than on-site must not be folded when shipped. White lines in the material should be taken as warnings of stresses induced by folding. Cracks can develop in these stressed areas. The bed or soil foundation on which the geosynthetic is to be placed must be examined to ensure that it is adequately compacted; free of rocks, roots, water and desiccation cracks; and free from herbicides that may react with the geosynthetic. Only after each roll or panel of geosynthetic material is examined and been found free of defects can it be placed in the landfill, with care taken to minimize movement during positioning. Inspection must determine that there is a firm foundation beneath the seam and that the geosynthetic is clean. Any defective seam must be bounded by seam areas that pass inspection tests; this entire bounded area must be repaired by a method agreed to in advance and must pass a careful visual inspection.
Inspection and sampling strategies for seams All seams must be visually inspected over 100% of their length. Visual inspection may detect dirt, debris, deep grinding marks, or moisture that may affect seam integrity. Field tests of seam continuity may also be made 100% of the seam length using various techniques. For example, an air
484
Robert E. Landreth
lance test may be used in which a low-pressure blast of air is focused on the seam edge; if the bond is loose, the seam will pop open. Other tests that may be made along the entire length of the seam include a vacuum chamber test, a pressurized dual seam test and an ultrasonic test. The above inspection and tests are nondestructive; no damage is done to the seam during the test. Destructive tests may be made on samples cut from the seam at sites that are subjectively determined (judgemental sampling) or randomly determined (statistical sampling). Judgemental sampling, resulting from an assessment of a well-trained operator or C Q A inspector, may take several forms. For example, the inspector may call for a sample to be taken at a location where conditions (e.g. deep scratches or moisture) might make the integrity of the seam suspect. Other situations include where a seaming operation begins, or where a new seamer begins work, or when an adjustment is made to the seaming equipment, etc. Seam samples for destructive testing may also be taken in a statisticallyselected random pattern. The pattern may have certain minimum requirements, such as at least one sample from every 500 ft of seam, or one per shift, or one per seam. Statistical sampling is not a substitute for judgemental sampling, nor vice versa. Both may be appropriate. In destructive testing, at least two tests are done: (1) a shear test to measure the continuity of tensile strength in the membrane and (2) a peel test to determine seam quality. Although statistical sampling may be done on seams, the use of statistics in testing seams is not appropriate. No failure is acceptable. Documentation
Documents must be kept while the FML is placed, inspected and tested. The placement log details the panel identity, subgrade conditions, panel conditions and seam details for every panel placed. Inspection documents must be maintained on all repairs, test sites, etc. A geosynthetic seam test log indicates the seam number, length, test methods performed, location and date of test and person performing the test. When the geosynthetic is completely in place, an as-built record of the landfill construction should be available to provide reviewers with an idea of the quality of the work performed as well as where any problems occurred.
PUBLIC NOTIFICATION A job well done should be recognized. Although most agree that financial payment usually completes the job, it should become a policy of the
Seamingof geosynthetics
485
designers ( A & E firms) that a paper be written and published on how the materials were selected, designed and installed. Did they perform as expected during the installations or were there problems? How were the problems corrected? What Q A procedures were used and were they adequate, too little or too much? We are all working in a very dynamic field. The public is suspicious of our claims. The University systems are not graduating a sufficient number of people to work in this area. It is the responsibility of manufacturers and users to instill more confidence in using geosynthetics, to provide more insight into how the materials have been used and their limitations and how we can ensure that the facilities being constructed today will meet the challenges of tomorrow.
SUMMARY The use of geosynthetics can provide the designer with materials that will satisfy the requirements, either legally or environmentally. The designer has the burden of transferring these materials into a design and then developing a plan to ensure the installation meets the design. However, the job is not over until the appropriate information is in the hands of the public. If we want the business to grow and be acceptable we must educate people to keep them interested and informed.
BIBLIOGRAPHY US EPA. Lining of waste containment and other impoundment facilities. EPA/600/2-88/052, US Environmental Protection Agency, Cincinnati, OH, 1988. US EPA. Seminar publication requirements for hazardous waste landfills design, construction and closure. EPA/625/4-89/022, US Environmental Protection Agency, Cincinnati, OH, 1989. US EPA. Technical Guidance Document: Construction quality assurance for hazardous waste land disposal facilities. EPA/530-SW-86-031, US Environmental Protection Agency, Cincinnati, OH, 1986. US EPA. Technical Guidance Document: The fabrication of polyethylene FML field seams. EPA/520/SW-89/069, US Environmental Protection Agency, Cincinnati, OH, 1989.
Seaming of Geosynthetics
Robert E. Landreth United States Environmental Protection Agency, Risk Reduction Engineering Laboratory, Cincinnati, Ohio 45268, USA
ABSTRACT Owners of containment facilities are using geosynthetics at an increased rate. A major concern in their use is the ability to field seam the materials such that the design function of the geosynthetic is transferred through the seam. This paper discusses potential concerns and describes quality assurance techniques that will, when utilized, help ensure that the facility will be constructed according to the design.
INTRODUCTION Field seaming of geosynthetics is probably the most critical of all the functions including design and installation. A great deal of skill is required in making a seam as strong as, as impermeable as, as chemically resistant as, etc., the parent sheet. From a public owner's perspective there should be no difference of any kind anywhere in the geosynthetic material. Since this condition cannot be met, what is the next best result that we can expect?
ISSUES OF C O N C E R N When geosynthetics are discussed they usually include geonets, geotextiles, geogrids, membranes and others. Their design function can be transmissivity or permittivity of liquids and gases, bedding or cushioning, hydraulic barriers or load transfer to mention only a few. The materials 481 Geotextiles and Geornembranes 0266-1144/90/$03.50I~) 1990 Elsevier Science Publishers Ltd, England. Printed in Great Britain
482
Robert E. Landreth
may be designed to act independently or as part of a total system. The designer will consider redundancies where performance is critical. The designer may also include redundancy where he knows that the joining of geosynthetics will be l©ss than perfect. The designer must address a variety of seam types, e.g. sewing of geotextiles, ties or rings for geonets and geogrids, and solvents, heat or others for membranes. He must take into account the site specific conditions such as the weather, foundation preparation, and the ability of the installation crew to install the materials according to the design function. A designer should know what seaming techniques work best for the material he is working with and must have some basis understanding of the limitations. As an example, if he knows that the finished seam characteristics will only represent 80% of the characteristics of the parent material the resultant design will take this into account. If he knows that the material will be placed under adverse environmental and site-specific conditions the d ea~gn will accommodate the concerns. The materials may have to be changed or a more detailed installation plan may have to be developed. Regardless of tile issues raised for a particular site, the designer should have at his disposal the necessary information to properly design and engineer geosynthetics to perform as desired.
CONSTRUCTION QUALITY ASSURANCE (CQA) FOR GEOSNTHETICS The Agency has long recognized that a good quality assurance plan can help bridge the gala between the owner/operator and the installers to obtain a facility that will be as good as or better than the design. Although this plan may be ~latively 0xpensive, many owner/operators will agree with the Agency's ¢iew because they can then be much more confident that the facility will be constructed according to the design. There are at least five elements of the CQA plan that when properly addressed will help ensure quality construction for geosynthetics: (1) responsibility and a~thority, (2) construction quality assurance (CQA) personnel qualifications, (3) inspection activities, (4) seam sampling strategies, and (5).documentation.
ResponslbilRyandauthority Because a geosynthetic may be manufactured by one company, fabricated by another, and installed by a third, various people have responsibilities within the construction process. They can include engineers who generally
Seaming ofgeosyntheacs
483
design the components and prepare specifications, manufacturers who fabricate the geosynthetic, and contractors who perform the installation. The recent growth in the geosynthetics industry makes it necessary to exercise care in selecting firms with proven experience in all aspects of their operation.
CQA personnel qualifications The C Q A officer should be a professional engineer or equivalent with sufficient practical, technical and managerial experience to understan4 H e assumptions made in the design of the facility and the install~ion requirements of the chosen geosynthetic. In order to build on this hard-to-find experience, some firms assign (but do not bill for) an engineer-in-training to work with the trained CQA officer on the job to develop field expertise.
Inspection Inspectors should be aware of the damage and defects geosynthetics can suffer during shipping, storing and placement. For example, highcrystaUinity membrane panels fabricated at the factory rather than on-site must not be folded when shipped. White lines in the material should be taken as warnings of stresses induced by folding. Cracks can develop in these stressed areas. The bed or soil foundation on which the geosynthetic is to be placed must be examined to ensure that it is adequately compacted; free of rocks, roots, water and desiccation cracks; and free from herbicides that may react with the geosynthetic. Only after each roll or panel of geosynthetic material is examined and been found free of defects can it be placed in the landfill, with care taken to minimize movement during positioning. Inspection must determine that there is a firm foundation beneath the seam and that the geosynthetic is clean. Any defective seam must be bounded by seam areas that pass inspection tests; this entire bounded area must be repaired by a method agreed to in advance and must pass a careful visual inspection.
Inspection and sampling strategies for seams All seams must be visually inspected over 100% of their length. Visual inspection may detect dirt, debris, deep grinding marks, or moisture that may affect seam integrity. Field tests of seam continuity may also be made 100% of the seam length using various techniques. For example, an air
484
Robert E. Landreth
lance test may be used in which a low-pressure blast of air is focused on the seam edge; if the bond is loose, the seam will pop open. Other tests that may be made along the entire length of the seam include a vacuum chamber test, a pressurized dual seam test and an ultrasonic test. The above inspection and tests are nondestructive; no damage is done to the seam during the test. Destructive tests may be made on samples cut from the seam at sites that are subjectively determined (judgemental sampling) or randomly determined (statistical sampling). Judgemental sampling, resulting from an assessment of a well-trained operator or C Q A inspector, may take several forms. For example, the inspector may call for a sample to be taken at a location where conditions (e.g. deep scratches or moisture) might make the integrity of the seam suspect. Other situations include where a seaming operation begins, or where a new seamer begins work, or when an adjustment is made to the seaming equipment, etc. Seam samples for destructive testing may also be taken in a statisticallyselected random pattern. The pattern may have certain minimum requirements, such as at least one sample from every 500 ft of seam, or one per shift, or one per seam. Statistical sampling is not a substitute for judgemental sampling, nor vice versa. Both may be appropriate. In destructive testing, at least two tests are done: (1) a shear test to measure the continuity of tensile strength in the membrane and (2) a peel test to determine seam quality. Although statistical sampling may be done on seams, the use of statistics in testing seams is not appropriate. No failure is acceptable. Documentation
Documents must be kept while the FML is placed, inspected and tested. The placement log details the panel identity, subgrade conditions, panel conditions and seam details for every panel placed. Inspection documents must be maintained on all repairs, test sites, etc. A geosynthetic seam test log indicates the seam number, length, test methods performed, location and date of test and person performing the test. When the geosynthetic is completely in place, an as-built record of the landfill construction should be available to provide reviewers with an idea of the quality of the work performed as well as where any problems occurred.
PUBLIC NOTIFICATION A job well done should be recognized. Although most agree that financial payment usually completes the job, it should become a policy of the
Seamingof geosynthetics
485
designers ( A & E firms) that a paper be written and published on how the materials were selected, designed and installed. Did they perform as expected during the installations or were there problems? How were the problems corrected? What Q A procedures were used and were they adequate, too little or too much? We are all working in a very dynamic field. The public is suspicious of our claims. The University systems are not graduating a sufficient number of people to work in this area. It is the responsibility of manufacturers and users to instill more confidence in using geosynthetics, to provide more insight into how the materials have been used and their limitations and how we can ensure that the facilities being constructed today will meet the challenges of tomorrow.
SUMMARY The use of geosynthetics can provide the designer with materials that will satisfy the requirements, either legally or environmentally. The designer has the burden of transferring these materials into a design and then developing a plan to ensure the installation meets the design. However, the job is not over until the appropriate information is in the hands of the public. If we want the business to grow and be acceptable we must educate people to keep them interested and informed.
BIBLIOGRAPHY US EPA. Lining of waste containment and other impoundment facilities. EPA/600/2-88/052, US Environmental Protection Agency, Cincinnati, OH, 1988. US EPA. Seminar publication requirements for hazardous waste landfills design, construction and closure. EPA/625/4-89/022, US Environmental Protection Agency, Cincinnati, OH, 1989. US EPA. Technical Guidance Document: Construction quality assurance for hazardous waste land disposal facilities. EPA/530-SW-86-031, US Environmental Protection Agency, Cincinnati, OH, 1986. US EPA. Technical Guidance Document: The fabrication of polyethylene FML field seams. EPA/520/SW-89/069, US Environmental Protection Agency, Cincinnati, OH, 1989.