Understanding the Strain on HDPE Liners

Insights from the PERMAS User’s Conference 

The PERMAS Users’ Conference provides a platform for engineers and researchers to discuss advances in finite element analysis. The event featured a presentation by Roelof Minnaar from ASM, written in conjunction with Stewart Chaperon and Ian de Villiers from TANDM. The presentation focused on the test methodologies used to evaluate the design of landfill sites and tailings storage facilities. The presentation highlighted the critical role that High-Density Polyethylene HDPE liners play in protecting the environment from harmful leachate (a potentially harmful liquid that forms when waste decomposes or tailings dewater) and discussed the methodologies employed to ensure their longevity and effectiveness.

Background: Landfills and Tailings Storage Facilities

Landfills and tailings storage facilities are essential components of modern waste management. Landfills handle solid waste and are designed to minimize the impact of waste on human health and the environment. Tailings storage facilities manage the by-products of metal ore processing, typically in liquid or slurry form. Both types of facilities require robust containment systems to prevent environmental contamination.

The Role of HDPE Liners

HDPE geomembranes are widely used to create impervious barriers between waste and the surrounding environment. Typically, these liners are 1.5 mm thick, supported by a 600 mm thick layer of compacted clay, and protected by a 100 mm thick layer of silty sand. The integrity of these liners is crucial for preventing leachate from contaminating groundwater.

Ensuring Longevity and Performance

The long-term performance of the HDPE liner is strongly dependent on the maximum tensile strain to which it is subjected. To ensure the longevity and performance of HDPE liners, rigorous testing and validation processes are necessary. The conference presentation detailed the method that TANDM developed for the in-situ testing of liners. The method uses aluminum foil to record deformation under applied loads ranging from 200 kPa to 600 kPa. This test aims to capture the deformation liners’ experience in real-world conditions.

Data Processing and Finite Element Analysis (FEA)

One key challenge in HDPE liner strain analysis is accurately deriving the liner strains from the measurement data. TANDM’s method involves a 3D scan of the deformed aluminum plates to generate a point cloud, which is then transferred onto a 1 mm x 1 mm grid.

Traditional methods approximate the liner strains from the grid points by considering gradients and curvatures in discrete directions. With the FEA approach, the grid points define the finite element mesh, and the measured deflections are applied as prescribed displacements. The finite element analyses include geometric and material non-linearities, providing a more realistic representation of the liner’s response under load.

Comparing Analytical Approaches

TANDM and ASM compared the different approximation methods to the strains computed with the FE model. The results highlighted the importance of including an estimate of the bending strain in any approximation. In areas of high curvature, the bending component contributes significantly to the outer fibre tensile strain and should, therefore, not be neglected in the strain estimate. By default, the FEA includes the bending component. Since the FEA approach is also not dependent on the choice of an axis along which the results are considered, it provides a much more reliable value for the maximum tensile strain in the membrane. This is crucial when comparing the performance of a design against the liner’s design criteria to achieve long-term safety and serviceability.


The presentation by ASM and TANDM showcased advancements in testing and analysis techniques and underscored the importance of using advanced simulation techniques to account for the complexities of liner behavior. Accurate strain values from the test data are essential for ensuring these liners’ effectiveness and longevity. A shift towards the more precise FEA methodology would be a significant step forward in engineering and environmental management, providing a robust framework for the ongoing development and optimization of containment systems.

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Vertical displacement of aluminium plate, plotted with deformation scale factor of 10
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