Doyin (Adesokan) James-Crutchlow Ph.D., P.Eng. (Project Director)
As Project Director, I liaise with the internal team, clients, and industry stakeholders for technical, design, and project needs. I also co-ordinate the site-specific performance-based testing programs, and oversee the client service experience throughout the project.
HDPE geomembranes are susceptible to stress cracking – a brittle failure below the yield stress of the geomembrane, caused by a highly crystalline microstructure (see e.g. – Rowe and Sangam 2002; Peggs 2003; Muller 2007; Scheirs 2009, Rowe et al. 2013; also Figure 1). A large number of facilities rely on the use of HDPE geomembranes for containment – think heap leach pads, tailings ponds, coal ash impoundments, landfills, leachate ponds, brine ponds, waste water facilities, storm water management, potable water storage, and more. Stress cracking in HDPE geomembranes has been the cause of many containment systems and facilities failing/reaching the end of their service lives prematurely, resulting in unwanted outcomes.
Here are some strategies for preventing or minimizing the risks of stress cracking in HDPE geomembranes.
- Choose HDPE geomembranes that are formulated with high quality additives and stabilizers. Good quality additives and stabilizers in HDPE geomembranes can increase stress cracking resistance from 500 (SP-NCTL hrs.) in a GRI GM-13 material to up to 1500 hrs. in a fortified material (Example – see Adesokan et al. 2018).
Choose HDPE geomembranes with high quality antioxidant packages. Such packages can help to reduce the antioxidant depletion rate in HDPE geomembranes when they are exposed to chemicals. Reduced antioxidant depletion rate can prolong the resistance of the materials to environmental stress cracking – which is, amongst several other factors, caused by the adverse reaction of geomembranes to chemicals under service conditions. To further highlight the benefits of good quality antioxidant packages, results presented by Abdelaal (2013), Morsy et al (2016)*, and Morsy et al (2021)* showed polyethylene (PE) geomembranes with high quality antioxidant packages performing better (slower antioxidant depletion rate, fewer surface cracks, and better tensile properties) than similar thicknesses of comparative PE materials, following exposure to chlorinated water. The better performance of those PE geomembranes was attributed to the resistance of their antioxidant package to depletion in chlorinated water, thus highlighting the benefits of high quality antioxidant packages for creating resistance to specific chemicals and solutions. The results from the Abdelaal (2013), Morsy et al (2016)*, and Morsy et al (2021)* studies also indicate that good quality antioxidant packages can boost chemical resistance for PE geomembranes where the microstructure of such a polymer may be expected to be limiting.
Manufacturers can apply surface treatments and finishes, such as texturing, differently onto HDPE geomembranes. For example, increasing the density of texturing (or asperity concentration) can help to better distribute across the geomembrane surface, point loads that would otherwise be carried by individual asperities. Spreading out point loads on more asperities can help to minimize or prevent inducing excessive localized strains that could cause stress cracking (see some discussions on stress cracking strains in Rowe and Sangam 2002; Peggs 2003; Peggs et al. 2005; Muller 2007; Scheirs 2009; Rowe et al. 2013).
- Proper designs; for example, appropriate slope angle β to interface friction angle δ (Figure 2), can help to prevent subjecting HDPE geomembranes to strains that may induce stress cracking.
- Proper backfilling approaches, such as backfilling from the bottom of the slope up, starting with a wide wedge at the bottom (Figure 2), can also help to prevent excessive tensioning in the geomembrane that could induce stress cracking strains later on.
6. Seek to use other alternatives that are not susceptible to stress cracking. For example, one from the same PE polymer base – LLDPE geomembranes, or others. High quality antioxidant packages in the polymer formulation (see point #2 above) can boost the chemical resistance of those alternative materials that may be considered to have a lower chemical resistance than HDPE geomembranes. For example, in Abdelaal (2013), Morsy et al (2016)*, and Morsy et al (2021)*, the chemical resistance of LLDPE geomembranes with high quality antioxidants was found to be as good as that of HDPE geomembranes for some solutions, and even better in some cases. It should however be noted that for any impermeable membrane material being considered, the performance-related properties of such material, relative to the expected site conditions, must be determined.
All the strategies presented above should be considered alongside other good design and construction practices, in order to achieve successful material performance in service. Ultimately, to assure the long term performance of constructions according to design and desired expectations, thorough site and project-specific evaluations of potential site materials need to be completed.
* The results in these references show a slower rate of antioxidant depletion in LLDPE geomembranes than in HDPE geomembranes, for some solutions. Nonetheless, the performance of the various materials varied widely in different solutions. The variabilities could be related to the testing conditions, differences in the resins, the additives and antioxidants in the resins, or a variety of other factors.
Such variabilities in findings highlight the need for site-specific evaluation of candidate materials for individual applications – a process that requires proper planning and organization to get the needed evaluation and testing done before hand. For any project to be successful, proper planning and extensive material evaluation is needed – remember the 5Ps “Proper Planning Prevents Poor Performance”. Further studies into the composition, including antioxidant packages, and chemical resistance of present-day HDPE and LLDPE geomembranes should also be completed to further evaluate the observations and indications that have been presented in the literature.
Terrasyntec will work with you throughout the planning, preparation, and decision making stages to the construction and post construction after care, to help you ensure the success of your project. Please forward your enquiries and questions to technicalservices@terrasyntec.com or fill out the form on our Contact page to engage with us.
References
Abdelaal, F. B., Rowe R.K., Brachman R.W.I, Thiel, R. 2013. Antioxidant Depletion from HDPE and LLDPE Geomembranes without Hals in an Extremely Low pH Solution. In Proceedings of the 2nd Pan American Conference on Geosynthetics, GeoAmericas 2012, April 2012, Lima, Peru
Adesokan, D., Marcotte B., Fleming, I., 2018. A comparison of HDPE geomembranes for response to strains that may be associated with stress cracking. In Proceedings of the 11th ICG Seoul South Korea, Sept. 2018
Morsy, M. S., Rowe, R. K., Abdelaal, F. B., 2021. Longevity of 12 geomembranes in chlorinated water, Canadian Geotechnical Journal, Vol. 58 (4). https://doi.org/10.1139/cgj-2019-0520
Morsy, M. S., Rowe, R. K., Abdelaal, F. B., 2016. Antioxidant Depletion from HDPE and LLDPE Geomembranes in Chlorinated Water. In Proceedings of the 3rd Pan American Conference on Geosynthetics, GeoAmericas 2016, 10-13 April 2016, Miami Beach USA
Muller, W. W. 2007. HDPE Geomembranes in Geotechnics, Springer, Berlin Germany
Peggs, I. D. 2003. Geomembrane Liner Durability: Contributing Factors and the Status Quo, Proc. UK IGS 2003 [http://www.geosynthetica.net/Uploads/IDPigsUKpaper.pdf]
Peggs, I.D., Schmucker, B., and Carey, P. 2005. Assessment of Maximum Allowable Strains in Polyethylene and Polypropylene Geomembranes, Proc. Geofrontiers 2005, Austin, Texas, USA
Rowe, R. K. and Sangam. H. P. 2002. Durability of HDPE geomembranes, Geotextiles and Geomembranes, Vol. 20, pp. 77–95.
Rowe, R.K., Brachman R.W.I., Irfan, H., Smith, M. E. and Thiel. R. 2013. Effect of Underliner on Geomembrane Strains in Heap Leach Applications. Geotextiles and Geomembranes, Vol. 40, 37-47.
Scheirs, J. 2009. A Guide to Polymeric Geomembranes, 1st Edition, Wiley and Sons, West Sussex, UK