From experience, the following situations should be paid much attention to when you weld geomembranes.
1) When geomembranes should be welded into a concrete building but can't be placed directly, a connecting lock made from the same materials with membranes should be embedded into the building before the geomembranes. Then you can weld geomembranes by conventional method.
2) If there are pipelines to go through the membranes, you should check the size and number of pipelines and melt the HDPE membranes with the prefabricated pipe liners first to prevent seepage.
3) Followings are what I learned from the imported geomembrane melting training in Solmax. If the weather is bad or there is force majeure, the project of melting should be stopped for one day or more. At the same time processed HDPE geomembranes should be fixed by earthbags for damage protection.
Solder skips should be avoided with particular attention.
