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Ever since polymers were first conceived as a material in construction, engineers were already creating product variations to hone the physical properties to best fit the needs of a project. In fact, before the term geosynthetics was even coined, the material was being used in projects such as the Delta Works in the Netherlands and the Valcros Dam in France (Kelsey 2014).
While there are notable differences that result from changes to the type of resin being used in a liner (linear low-density polyethylene [LLDPE] vs. high-density polyethylene [HDPE], for instance), among the most significant differences come from changes to a polyethylene liner’s thickness. In this article, we will explore high-density polyethylene liners, two size categories and applications best suited for those sizes.
A primer on polyethylene liners and thickness
The properties of a polyethylene liner are primarily determined by its molecular structure and its thickness. Additives can also affect the performance of the liner especially at it relates to long-term performance.
When it comes to molecular structure, the polymers in polyethylene can be structured in several ways to affect its overall tensile strength, density and permeability. Each configuration varies in the amount of branching present and the overall length of the chains. HDPE, for example, has minimal branching of its polymer chains and is therefore more rigid and has a higher density when compared with LLDPE. HDPE liners will also confer several benefits regardless of its thickness, such as its high resistance to corrosion, enhanced chemical resistance and long-term UV resistance.
Beyond molecular structure and chemical composition, the next most significant attribute is a polyethylene liner’s thickness. HDPE liners are typically available from 30 to 120 mil (0.8–3 mm), with the thickness affecting the liner’s overall permeability, strength, weight, roll length, flexibility and cost. Properties like a liner’s permeability, for instance, are directly proportional to its thickness. So, it is possible to choose a liner thickness that aligns with the specific needs of a project. In fact, the thickness should be determined during the planning stage of the project and be set based on the expected stresses that will be experienced by the liner (Topliff 2018).
An overview of the 40-mil polyethylene liner
The most common HDPE liner size is 40 mil (1 mm), which offers a balance in strength, permeability and cost. HDPE liners of this thickness are typically used for applications such as potable and reserve water, as well as containment, agricultural and dairy ponds.
While a 40-mil HDPE liner offers less overall strength and puncture resistance than its thicker counterparts, the thinner liner offers cost benefits. A 40-mil HDPE liner will be less expensive and will also be cheaper to transport per square foot of lined area than a thicker option. The 40-mil HDPE liner is also easier to install because it will have a longer roll length, which reduces the number of cross seams installers will need to weld.
The 40-mil HDPE liner is typically used for agricultural pond applications and other relatively noncritical applications. For these applications, the 40-mil HDPE liner serves to support the containment layer by preventing the pond’s contents from leaching out into the surrounding environment.
An overview of the 60-mil polyethylene liner
Another common HDPE liner size is 60 mil (1.5 mm), which offers an increase to physical strength and is less permeable than the 40-mil variant. The liner’s increased thickness and strength also offers improved weathering resistance, making it better suited for exposed applications.
Projects that must meet rules by regulatory bodies such as the Environmental Protection Agency (EPA) should adhere to a minimum thickness for its HDPE liners. In landfill containment of nonhazardous waste, for instance, the EPA requires a minimum nominal thickness of 60 mil for flexible membrane liners made with HDPE. These requirements were set to help reduce the potential for tearing or puncturing.
Additionally, a designer will also specify a 60-mil HDPE liner—or thicker—for applications requiring greater liner strength or lower permeability. They can also choose to specify a thicker liner if they calculate that a thinner liner is not likely to stand up to a region’s 100-year weather event. Thicker liners are also better suited for regions with seismic activity.
References
Kelsey, Chris. (2014). “A brief history of geotextiles: A 40-year update.” Land and Water. March/April, 8–13.
Topliff, C. R. (2018). “Uses and installation of HDPE liner to reduce soil erosion and prevent water loss.” https://wtamu-ir.tdl.org/handle/11310/153. Accessed in June 2019.
This article first appeared on the AGRU America blog, https://agruamerica.com/blog.