Cellular confinement systems (CCS; also known as geocells) are widely used in construction for erosion control, soil stabilization on flat ground and steep slopes, channel protection, and structural reinforcement for load support and earth retention.Geosynthetics in landscape architecture and design Typical cellular confinement systems are geosynthetics made with ultrasonically welded high-density polyethylene (HDPE) strips or novel polymeric alloy (NPA)—and expanded on-site to form a honeycomb-like structure—and filled with sand, soil, rock, gravel or concrete.State of California Department of Transportation, Division of Environmental Analysis, Stormwater Program. Sacramento, CA."Cellular Confinement System Research." 2006.Managing Degraded Off-Highway Vehicle Trails in Wet, Unstable, and Sensitive Environments , US Department of Agriculture in conjunction with USDOT, Federal Highway Administration. Page 28. October 2002.
History of cellular confinement Research and development of cellular confinement systems (CCS) began with the U.S. Army Corps of Engineers in 1975 to devise a method for building tactical roads over soft ground.Webster, S.L. & Watkins J.E. 1977, Investigation of Construction Techniques for Tactical Bridge Approach Roads Across Soft Ground. Soils and Pavements Laboratory, US Army Corps of Engineers Waterways Experiment Station, Vicksburg, MS, Technical Report S771, September 1977. Engineers found that sand-confinement systems performed better than conventional crushed stone sections and they could provide an expedient construction technique for access roads over soft ground, without being adversely affected by wet weather conditions.Webster, S.L. 1979, Investigation of Beach Sand Trafficability Enhancement Using Sand-Grid Confinement and Membrane Reinforcement Concepts – Report 1, Geotechnical Laboratory, U.S. Army Corps of Engineers Waterways Experiment Station, Vicksburg, MS, Technical Report GL7920, November 1979.Webster, S.L. 1981, Investigation of Beach Sand Trafficability Enhancement Using Sand-Grid Confinement and Membrane Reinforcement Concepts – Report 2, Geotechnical Laboratory, U.S. Army Corps of Engineers Waterways Experiment Station, Vicksburg, MS, Technical Report GL7920(2), February 1981 The US Army Corps of Engineers in Vicksburg, Mississippi (1981) experimented with a number of confining systems, from plastic pipe mats, to slotted aluminum sheets to prefabricated polymeric systems called sand grids and then, cellular confinement systems. Today cellular confinement systems are typically made from strips 50–200 mm wide, ultrasonically welded at intervals along their width. The CCS is folded and shipped to the job site in a collapsed configuration.
Efforts for civilian commercialization of the cellular confinement system by the Presto Products Company, led to the Geoweb®.Prestogeo.com This cellular confinement system was made from high density polyethylene (HDPE), relatively strong, lightweightWebster, S.L. 1986, Sand-Grid Demonstration Roads Constructed for JLOTS II Tests at Fort Story, Virginia, Geotechnical Laboratory, U.S. Army Corps of Engineers Waterways Experiment Station, Vicksburg, MS, Technical Report GL8619, November 1986. and suitable for geosynthetic extruding manufacturing. The cellular confinement system was used for load support, slope erosion control and channel lining and earth retention applications in the United States and Canada in the early 1980s.Richardson, Gregory N. "Geocells: a 25-year Perspective Part ‘l: Roadway Applications." Geotechnical Fabrics Report (2004).Richardson, Gegory N. "Geocells, a 25-year Perspective Part 2: Channel Erosion Control and Retaining Walls." Geotechnical Fabrics Report 22.8 (2004): 22-27.Engel, P. & Flato, G. 1987, Flow Resistance and Critical Flow Velocities for Geoweb Erosion Control System, Research and Applications Branch – National Water Research Institute Canada Centre for Inland Waters, Burlington, Ontario, Canada, March 1987Bathurst, R.J, Crowe, R.E. & Zehaluk, A.C. 1993, Geosynthetic Cellular Confinement Cells for Gravity Retaining Wall – Richmond Hill, Ontario, Canada, Geosynthetic Case Histories, International Society for Soil Mechanics and Foundation Engineering, March 1993, pp. 266-267Crowe, R.E., Bathurst, R.J. & Alston, C. 1989, Design and Construction of a Road Embankment Using Geosynthetics, Proceedings of the 42’nd Canadian Geotechnical Conference, Canadian Geotechnical Society, Winnipeg, Manitoba, October 1989, pp. 266–271
Research
Early researchBathurst, R. J. & Jarrett, P. M. 1988, Large-Scale Model Tests of Geocomposite Mattresses Over Peat Subgrades, Transportation Research Record 1188 – Effects of Geosynthetics on Soil Properties and of Environment on Pavement Systems, Transportation Research Board, 1988, pp. 2836 found that cellular confinement reinforced gravel bases are "equivalent to about twice the thickness of unreinforced gravel bases" and that geocells performed better than single sheet reinforcement schemes (geotextiles and geogrids) and were more effective in reducing lateral spreading of infill under loading than conventional reinforced bases. However, Gregory N. Richardson (who was onsite at the US Corps of Engineers CCS Vicksburg facility) laments 25 years later on the "near absence of research papers on geocells in all of the geosynthetic national and international conferences."Richardson, Gregory N. "Geocells: a 25-year perspective Part ‘l: roadway applications." (2004)
A comprehensive literature review in 2008 concluded that the use of CCS technology in base reinforcement of paved roads, and railways in particular, was limited, due to the lack of design methods, lack of advanced research in the previous two decades and limited understanding of the reinforcement mechanisms.Yuu, J., Han, J., Rosen, A., Parsons, R. L., Leshchinsky, D. (2008) “Technical Review of Geocell-Reinforced Base Courses over Weak Subgrade,” The First Pan American Geosynthetics Conference & Exhibition proceedings (GeoAmericas), Appendix VII, Cancun, Mexico Since then, hundreds of research papers on geocell systems have been published. Extensive research has been conducted on CCS reinforcement for roadway applications to understand the mechanisms and influencing factors of confinement reinforcement, evaluate its effectiveness in improving roadway performance and develop design methods for roadway applications.
Comprehensive surveys and reviews—presented in 2017 and 2020—of latest geocell studies, field testing, state of the art knowledge and present trends and scope of future research directions, validated increased use of geocells in ground reinforcement and infrastructure projects. In 2013, J. Han et al. summarized comprehensive research conducted at the University of Kansas, including static and cyclic plate loading tests, full-scale moving wheel tests, and numerical modeling on geocell-reinforced base courses with different infill materials and discussed the main research findings from these studies regarding permanent, elastic, and creep deformations, stiffness, bearing capacity, and stress distribution, and the development of design methods for geocell-reinforced bases. These studies showed that base courses reinforced with Novel Polymeric Alloy (NAP) geocells reduced the vertical stresses at the interface between subgrade and base course, reduced permanent and creep deformations, increased elastic deformation, stiffness, and bearing capacity of base courses.Han, J., Thakur, J.K., Parsons, R.L., Pokharel, S.K., Leshchinsky, D., and Yang, X. (2013) Additional literature reviews were performed in 2013 by O. Kief et al. and A. Marto et al.Marto, A., Oghabi, M., Eisazadeh, A., (2013), Electronic Journal of Geotechnical Engineering. vol 18, Bund. Q., 3501-3516
Recent innovations in cellular confinement technology
The strength and stiffness of pavement layers determines the performance of highway pavements while aggregate use impacts the cost of duration of installation; therefore alternatives are needed to improve pavement quality using new materials with less aggregate usage.Rajagopal, K., Veeraragavan, A., Chandramouli, S. (2012). “Studies on Geocell Reinforced Road Pavement Structures,” Geosynthetics Asia 2012, Thailand Geocells are recognized as a suitable geosynthetic reinforcement of granular soils to support static and moving wheel loads on roadways, railways and similar applications. But stiffness of the geocells was identified as a key influencing factor for geocell reinforcement, and hence the rigidity of the entire pavement structure.Emersleben, A. (2013). “Analysis of Geocell Load Transfer Mechanism Using a New Radial Load Test. Sound Geotechnical Research to Practice 2013. GeoCongress, San Diego, 345-357
Laboratory plate loading tests, full-scale moving wheel tests, and field demonstrations showed that the performance of geocell-reinforced bases depends on the elastic modulus of the geocell. Geocells with a higher elastic modulus had a higher bearing capacity and stiffness of the reinforced base. NPA Geocells showed higher results in ultimate bearing capacity, stiffness, and reinforcement relative to geocells made from HDPE.Pokharel, S. K., Han J., Leshchinsky, D., Parsons, R. L., Halahmi, I. (2009). “Experimental Evaluation of Influence Factors for Single Geocell-Reinforced Sand,” Transportation Research Board (TRB) Annual Meeting, Washington, D.C., January 11–15 NPA geocells showed better creep resistance and better retention of stiffness and creep resistance particularly at elevated temperatures, verified by plate load testing, numerical modeling and full scale trafficking tests.Han, J., Pokharel, S. K., Yang, X. and Thakur, J. (2011). Unpaved Roads: Tough Cell - Geosynthetic Reinforcement Shows Promise, Roads and Bridges, 40-433. Pokharel, S .K., Han, J., Manandhar, C., Yang, X. M., Leshchinsky, D., Halahmi, I., and Parsons, R. L. (2011). “Accelerated Pavement Testing of Geocell-Reinforced Unpaved Roads over Weak Subgrade.” Journal of Transportation Research Board, 10th Int’l Conference on Low-Volume Roads, Florida, USA, July 24–27
Application vs. long-term performance CCS have been successfully installed in thousands of projects worldwide. However, it is incumbent to differentiate between low load applications, such as slope and channel applications, and new heavy-duty infrastructure applications, such as in the base layer of motorways, railways, ports, airports and platforms. For example, while all polymeric materials in CCS will creep over time under loading, the questions are; how much permanent degradation will occur, under which conditions, and its impact on long-term performance, and if this may lead to failure.Jain, R.K. (2013). Creep Behaviour of Geosynthetics for Sustainable Construction. Research Journal of Chemical Y Environmental Sciences, 1 (5), December. 34-46.Koerner, R.M., Koerner, G., Hsuan, Y. (2014). Creep Tension Testing of Geosynthetics, Geosynthetic Institute. GSI White Paper #29, July 26.
The lifespan of CCS in slope protection applications, for example, is less critical as vegetative growth and root interlock help stabilize the soil. This in effect compensates for any long-term loss of confinement in the CCS. Similarly, load support applications for low volume roads not subject to heavy loading typically have a short design life; therefore minor loss of performance is tolerable. However, in critical infrastructure applications such as reinforcement of the structural layers of highway pavements, railways and platforms, long-term dimensional stability is critical. As long as the volumetric area of the geocell does not change more than 2-3%, compaction and performance is maintained and settlements are minimized.ISO Standard WD TR 18228-5. (2018). Design using Geosynthetics – Part 5: Stabilization. International Organization for Standardization. Geneva, Switzerland. Under development.