Introduction
In geomembrane jobs, the quality of the geomembrane itself is only half of the equation. The real success or failure of a liner system comes down to how effectively the seams are welded in the field. You can have a fantastic grade of HDPE geomembrane, but if the welding is not carried out properly, it is all for nothing.
A landfill liner, an aquaculture pond, a mining containment system, welding is what meshes together discrete sheets into a single continuous impermeable barrier. Understanding what geomembrane welding is, helps educate both project owners and contractors alike to prevent leakage that puts the project in jeopardy down the line.
Key Explanation
In a geomembrane installation, the term welding refers to the joining of adjacent liner sheets using heat and/or pressure and/or extrusion.
The aim is to secure seams as strong as or stronger than the parent material and impervious to it.
The three methods used in the industry today are:
Hot wedge welding (double track welding)
Perhaps the most popular welding method for HDPE geomembranes, a heated wedge passes between the overlapping sheets. The surfaces are melted, and pressure rollers force the sheets together into a strong, dense seam. Two parallel welds are created, with an air channel down the middle of the weld for testing.
Hot air welding
Hot air is introduced between the liners to soften the material, before pressure to force the sheets into conjunction. Typically this is used on thinner geomembranes and/or LLDPE material. It is also frequently used for some detail working where the wedge welder has difficulty.
Extrusion welding
This technique is used where a seam cannot be double welded, an area being repaired, or a technical feature like a pipe penetration perhaps. A polymer is extruded onto the edge of the seam, joining the sheets.
Surface Preparation
Surface preparation is essential to this method, to ensure proper adhesion.
Control of Temperature, Speed and Pressure
Each method requires strict control of temperature, speed and pressure – varying one small part of that triad has a major effect on the strength of the weld.
Applications / Use Cases
Landfill Liners
Hot wedge welding is generally preferred for large landfill projects, on account of speed and the requirement for consistent seam quality. The double-track weld also permits of air pressure tests not involving mechanical destruction.
Aquaculture Pond Liners
Wedge and hot air welding are used both – depending on the thickness of the liner. When properly welded, there is zero leakage which is absolutely essential for both the retention of water and with regard to contamination.
Mining – Geomembrane Systems
Mining applications usually entail the use of relatively thick HDPE geomembranes – hot wedge welding is mainly used. Extrusion welding for detailing is also employed.
Water Containment and Reservoirs
Reliable seams are of course absolutely essential when these are put into use. Quality of welding does have a bearing on long-time performance where the membranework is left exposed to the out-doors.
Biogas Digester Covers
A gas-tight seam is again required and this depends on welding and tests for that purpose of a most stringent kind.
Comparison or Benefits
Depending on the conditions, each method will have its place. Hot wedge welding, however, is widely adopted for the obvious reasons outlined.
Hot air welding is less stringent and lends itself better to smaller or more detailed sections although it makes no claims to join thermoplastics together with the strength of wedge welding for thicker materials.
Extrusion welding has the advantage of producing a strong bond for repairs and complex joints at the same time as lending itself to a slower speed and being very operator dependent in quality.
From a project point of view, good overall welding reduces the chance of leaks, lengthens the overall life of the geomembrane liner and results in lower maintenance costs in the long run.
How to Choose / Buy
Choosing the correct welding procedure is determined by:
The type of material and its thickness
Hot wedge welding is specified as an industry standard for HDPE geomembranes. In the case of thin, soft materials, hot air welding may be used.
Project scale
For large projects the speed and efficiency of automated wedge welding machines is beneficial. For smaller or difficult to reach areas, use of manual techniques is indicated.
Site conditions
Temperature, humidity, barometric pressure, wind can all affect the quality of the weld. Temperature and other parameters may need to be adjusted accordingly.
Contractor experience in welding
Most of the quality of welding will depend upon the foreman and the welders themselves. Often it is advisable to ask for actual records of testing from the contractor who is actually doing the work, so as to judge what to expect. A truly bonded seam is essential for a successful installation. What you find that has been done is a good indication of things to come.
When purchasing geomembrane systems it is advisable to select a supplier who is adept not only in providing you with the material, but also with useful help in the area of welding of the seams, and making themselves available to answer questions regarding “the way it should be done” in the area of installation.
FAQ
What is geomembrane?
A geomembrane is an impermeable synthetic fate or barrier with a wide variety of civil engineering applications, including geoengineering projects such as landfills, ponds and hydraulic fracturing.
How does it work?
It serves as a barrier layer, preventing any leakage. Individual sheets are used which, on being welded at the seams, converts to a continuous lining system that retains the liquid or gas in the purpose.
Cost or lifespan?
Cost lies in the eye of the beholder, but often depends on the thickness or material that is used. On one system sold as HDPE geomembrane, the manufacturer claims that if installed properly, provided a good weld is made at the seams, the liner will “last anywhere from 10 to 20 years”.
Best option?
HDPE geomembrane is by far the best option for a large site, with hot wedge welding to connect the sheets being a good accepted means of proceeding. The point is that it all depends on applications, possible site conditions.
What are common problems?
Poor welding of the seams at the seams is by far the most common problem when installing geomembranes. Improperly applied seams are also conducive to; weak seam bonding, contamination forming at the seam or along the seam. All these are very detrimental and may or may not be patched, depending on how pervasive they are, but all can lead to leakage eventually.