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Everything you need to know

about geomembranes

    • Geomembranes have been used for many decades for the containment of wastewater. The features of the material, its durability, behaviour and price mean that in some places it has become a standard product. Some people even think of it as a simple construction material for which price is all that matters. However, as geomembranes are the only barrier between the soil and contaminating waste, they must be classed as a security product. Our commitment is to manufacture the most secure possible products in the industry. (Photograph of climber)
    • The product must meet the specific needs of individual customers. It must satisfy local legislation, even for labelling and transport, and there are also requirements in terms of certificates, regulations, standards and laws. Each project or application has specific requirements that make it unique. Nonetheless, we should not forget the importance of consistent standards that apply across countries and customers to ensure the secure containment of standard contaminating products. Safe Containment is achieved by observing specific limits that are common throughout the world.
    • A textured product may or may not be required. Textured products should only be used if necessary; otherwise, a smooth product should be used. This may seem obvious but it is an important distinction, especially since in many projects the designation of products as textured is confusing and misleading, with some smooth products described as being textured. Clarifying the customer’s requirements is a key part of providing the correct solutions under conditions that are clear for other companies.
    • Is a wider geomembrane roll better? There is a technical limitation in the manufacture of geomembranes. The limit for HDPE is 7.5 m, above which a more fluid material, such as LLDPE is required to allow the machine’s extrusion head to complete the transformation cycle for the geomembrane. Otherwise, consistency of the thickness or thermal treatment of the raw material can be seriously compromised on the surface and at the edges. Within these limits and above a minimum width at which it would not be feasible to supply a secure containment product, roll width is a choice made by the manufacturer
    • and is commonly determined by the supply format and the optimisation of transport costs. There is hardly any difference in machinery costs depending on thickness. Within these limits, a wider format can offer a modest reduction in installation costs for large projects, although this can be offset by higher handling costs from heavier spools and overruns when finishing curves or corners. The second layer of the security barrier is normally a bentonite product that acts as a secondary barrier. However roll widths vary and welds, which are always weak spots, often coincide. At Atarfil, we generally recommend crossing products to adjust to avoid problems caused by the different widths.
    • Linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE) are similar raw materials in terms of their composition but, as noted elsewhere, behave very differently. HDPE has become an international standard for secure containment, precisely because of its unique properties. As such, LLDPE is often passed off as HDPE, a practice that is like offering a substitute product without any benefits for the customer. It is extremely easy to distinguish between the two materials: the MFI for HDPE will be < 1.2 for 190/5 kg. It’s as simple as that. What’s a TPO? TPOs are thermoplastic polyolefin geomembranes that can be made from different proportions of any of the four polyolefins. As each polyolefin has its own properties and a different base price, it is impossible to compare the properties and price of two TPO products without knowing their specific mix.
    • Although you might think that determining the thickness of a geomembrane should straightforward, there are a number of subtleties that mean this is not always the case. It’s important to distinguish between the average thickness and the ± tolerance percentage, which varies depending on the manufacture process. These two properties are clearly defined and the customer can be sure of buying a specific product weight, which is given by the area, the average thickness and the density of the product. This is a physical principle and allows comparison between different products. However, the situation becomes less clear when we talk about “nominal” or rated thickness, which leaves manufacturers free to “label” their products as having a given thickness, even though the small print states that the minimum average thickness is the nominal thickness “minus” 10%, with a tolerance of –10%.
    • In other words, the product may be at least 20% of the “nominal” thickness. You can decide for yourself what this means.
    • You might expect a wrinkle caused by expansion or the detachment of the geomembrane from the supporting soil to return to normal as soon as the temperature falls back to its initial state. There are a number of reasons why this might not be the case.
      ⦁ The geomembrane has its own weight and angle of repose on the support interface with its base and can thus store captured stress. This means that geomembranes directly laid on the soil will behave differently from those supported by geotextiles.
      ⦁ Likewise, geomembranes on slopes, in which expansion wrinkles gravitate downward due to the weight of the material and then must recover from this gravitational effect, are different from geomembranes installed on a flat surface, since the wrinkle recovers immediately.
      Based on the two points above, the installer must be aware of the level of expansion of the geomembrane’s panels throughout the day and ensure it does not accumulate too much captured stress, which would prevent it from fully recovering from the wrinkles and detachments at the end of the day. If these do not return to normal, the temperature control has been insufficient and it will be necessary to study their influence on the installation of the geomembrane to adopt the necessary corrective measures. It is also useful to recall that at a given location, the ambient temperature changes throughout the year. The end customer will normally choose the installation date for the geomembrane and this decision will determine the temperature range during installation. This means there will be a “final” temperature at the end of the geomembrane installation, which may differ from the average temperature at the site. If the work is completed in the middle of winter, large wrinkles can be expected in the summer. Similarly, if the work is completed in the middle of the summer, there will be detachments in the winter. The above holds true for exposed geomembranes. However, if the geomembrane is covered by liquids or solids, their temperature will determine the real situation. Given these factors, the installer may choose to work during the night in summer to reduce the final temperature or work during the middle of the day in winter to increase the temperature. Please remember, however, that this approach has its limits.