Hosted on April 30 by ASTM D35, with the support of IAGI and the Technical Committee on Barriers of the IGS (TC-B)
Panelists
Eric Blond, Consultant, ASTM D35.10 (moderator)
Amir Shahkolahi, Global Synthetics, IGS TC-B (moderator)
Kerry Rowe, Queens University
George Koerner, Geosynthetic Institute
Eddie Weiser, Leister
Dave McLaury, Consultant
Todd Harman, Hallaton
Eric Lamontagne, GE Environmental
Richard Thiel, Thiel Engineering
(the slides of the short introduction presentation made by each panelist is available at the end of this page)
Context
Several structures lined with geosynthetics are located in regions which may be exposed to low temperatures. Installers may find themselves obliged to install, and weld geomembranes under conditions which are historically considered to be inappropriate to weld polyethylene, sometimes against their will, and/or because of a variety of external reasons ranging from bad weather / act-of-God to bad planning or poor management of other components of the project such as earthwork and subgrade preparation. Consequently, installation and welding of geomembranes has become part of common practices. How good is this for the quality of the structures, for the installers, and eventually for the owners? Are there techniques available to deliver high quality seams? This 90-minute discussion panel will bring together Research, Installers, Geomembrane and Welding equipment Suppliers, as well as QA Engineers to discuss what should be reasonable limits, from a practical prospective and considering the contractual and environmental conditions of such projects.
Key outcome of the panel
There will always be a need for geomembrane deployment over a wide range of
temperatures and environmental conditions. The panel discussion was focused on the
question of how to tackle Geomembrane welding at extreme cold temperatures. Typically,
most geomembranes can be installed at temperatures down to 5°C without adaptions to
installation methods. The Panel discussion concentrated on the necessary requirements needed to be observed when welding below these temperatures with a range of suggestions made as to lessen the problems associated with Cold Weather Seaming.
A consensus was reached on several points, and will lead to the update of technical guidances in the near future. In particular:
Geomembranes should be welded at a temperature above -15 to -20 deg.C
Excessive moisture is a bigger problem than low temperature.
Wind barriers should be used instead of tents covering the seamed area, as tents may favour the capture of humidity.
Welding too fast at a too high temperature is not recommended.
Increasing a little bit the length of the wedge may facilitate using lower welding temperature.
Data recording should be used to monitor the entire welded length.
Extrusion bead should be maximum 2x the thickness of the sheet.
Thickness reduction should be documented, but more research is needed to define a criteria, i.e., maximum thickness reduction.
The EPA report from 1991 describing how to weld geomembranes must be revisited and updated.
Furthermore:
Subgrade preparation will be more challenging and planning for these difficulties must be considered.
At temperatures below zero there will be a loss of Geomembrane flexibility, and this must be considered as deployment will be more difficult.
Rub or drag sheets should be used as rocks and sharp stones are more likely to cause damage under cold harsh conditions. Snow and frost must be removed before any welding is to take place.
Winds must be considered as wind damage is a real concern with cold stiff membranes. Under windy conditions a wind break may be preferable as a tent may promote a humid environment which could then cause dew point issues.
The thickness of the geomembrane must be considered due to the harsher prevailing conditions.
The Panel determined that a lower temperature limit between -15/ -20 °C be established.
No seaming during precipitation or snowfall.
More trial welds and subsequent testing will be required and must be incorporated.
Profile of extrusion welds need to be optimised with the panel recommendation of a maximum height of 2 times the thickness of the membrane being deployed.
Longer wedges could be used during fusion welding as this would allow more energy to be used during the welding process without the use of excessive welding temperatures. Conservative welding speeds would also most likely be needed.
It was considered that the use of welders with data acquisition systems was necessary. Fusion welders with these abilities display all 3 welding parameters (temperature, speed and pressure). This then also enables post welding analysis to take place.
Weld thickness reduction should be documented, but more research is needed to define if and how useful such data is under these conditions.
It was considered prudent that documents such as "The EPA report from 1991 describing how to weld geomembranes" could be revised and used. ASTM is also developing a Guide to welding of Polymer Geomembranes.
A copy of the slides of the short introduction presentation made by each panelist is available here:
Comments