At the recent GeoANZ conference in Melbourne, Jonathan Shamrock from Tonkin & Taylor Ltd presented a compelling proposal to adjust the GRI GM19 standard. His presentation focused on a significant gap in the current standard: the need for more requirements for long-term durability related to oxidative induction time (OIT) loss within the weld zone of HDPE geomembranes. Shamrock’s proposal seeks to align the GRI GM19 standard more closely with the German DVS standard for weld thickness reduction. This suggestion has sparked considerable debate among industry professionals, and rightly so.
The Current GRI GM19 Standard: A Strength-Based Approach
The GRI GM19 standard primarily emphasises weld strength, ensuring that geomembrane seams maintain their structural integrity. However, Shamrock highlighted a critical oversight: the standard does not address long-term durability issues linked to OIT loss in the Heat Affected Zone (HAZ) adjacent to the weld. OIT is crucial for assessing the long-term oxidative degradation resistance of geomembranes, an aspect not covered by merely evaluating weld strength.
The German DVS Standard: A Model for Improvement
The DVS standard in Germany includes a range of thickness reduction limits during welding, which serves as a proxy for controlling the amount of heat and pressure applied during the welding process. By minimising thickness reduction, the amount of heat introduced into the geomembrane is controlled, which helps preserve OIT values in the HAZ adjacent to the weld. This approach ensures that the geomembrane's long-term durability is not compromised by excessive heat during welding. At a cold weather welding workshop, arranged by Eric Blond and reported on by Goerge Koerner, held at the GeoAmericas conference in Toronto in April 2024, the panel concluded that a 10% thickness reduction may be a good indication of long-term seam quality. This needs to be applied, however looking at the complete welding ecosystem, so including limits on weld temperature, weld pressure and weld speed.
Practical Implications of the 10% Thickness Reduction Proposal
Shamrock’s proposal to adopt a similar 10% thickness reduction limit in the GRI GM19 standard has several implications:
Heat/Pressure Management: Reducing thickness reduction likely means less heat/pressure can be applied during welding, which in turn helps maintain OIT values and long-term durability.
Slower Welding Process: Less heat typically means a slower welding process, which could impact project timelines and costs.
Material Quality Concerns: Many lining contractors have expressed concerns that current materials, especially those that are produced through blown film techniques or with blended or recycled resins, may struggle to meet this requirement. In Germany, where this practice is already in place, the materials used are of high quality and consistency, particularly in thickness and resin composition. CQA is also of a very high standard and verifies these details.
The Challenge of Inconsistent Materials
One of the significant challenges is the inconsistency in material quality. PE resins with variable melt flow and thickness can complicate the welding process, particularly if needing to be consistent without the ability to adjust parameters in real-time. Current welding technologies, like wedge welders, cannot automatically adjust pressure, temperature, and speed in real time, which exacerbates the issue when dealing with inconsistent materials.
A Path Forward: Integrating Quality Specifications
For the 10% thickness reduction requirement to be effective, it was suggested that this specification change should be accompanied by details regarding manufacturing techniques and resin types / HDPE properties, along with construction quality assurance (CQA) checks. Ensuring material consistency from the outset could mitigate many of the concerns raised by lining contractors.
Industry Reaction and the Need for Collaboration
The response from the lining contractors has been largely sceptical, with many doubting the practicality of this requirement on-site. Concerns about slowed installations and increased costs for end users are valid and warrant further discussion. However, this proposal represents a significant step forward in enhancing the long-term durability of containment facilities and managing the long-term risks from these.
Conclusion: Balancing Innovation with Practicality
While Shamrock’s proposal to adjust the GRI GM19 standard to include a 10% thickness reduction limit, akin to the DVS standard, is a progressive move for the industry, it becomes essential to address material quality and manufacturing consistency to ensure this change is feasible. Combining this change with stringent specifications could lead to safer, more durable containment solutions, balancing innovation with on-site practicality. Further collaboration with installers and material manufacturers is essential to understand the hesitations and develop a practical implementation strategy.
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