Editor’s note: Feature articles in Geosynthetics magazine focus on projects and how geosynthetic materials are used in a variety ofapplications. Very rarely is the focus solely on a specific product, company, or individual. Professor Leshchinsky and I note that this article—particularly the Introduction and Conclusions—departs from this policy in an effort to offer a guideline, an example, of how product development for the geosynthetics industry can be done effectively. We hope these lessons can further advance the geosynthetics industry into the 21st century with much success.—RB

Innovation has always required thinking out of the box. The development of various applications-oriented geosynthetic products demonstrates this hypothesis. For example, consider geomembranes, geogrids, and geotextiles, and think of landfills, MSE walls, and filters. While geotechnical structures become more cost-effective and have better performance, researchers are rewarded for positively impacting the profession.

An established player in the geocells arena, PRS-Mediterranean, envisioned a modification of its standard product to enable new, critical applications. The idea was to develop a new polymeric alloy that combines the desired properties of polyethylene and polyester, thus enabling an effective use of geocells as reinforcement for earth retention, load support in pavements and railroads, and more. While exploring the production of such an alloy (called Neoloy®), PRS commissioned research to develop design methodologies. Such research should also imply the desired properties of the new product.

This article provides an overview of the research where the use of geocells as an earth-retention structure was explored. The geocell used in the tests was standard, commonly used HDPE and, as such, was not appropriate for long-term reinforcement applications; that is, it was not stiff enough. However, it was adequate for investigation of short-term performance, thus implying the desired long-term properties of a polymer to be used as well as producing the basis for design, especially under severe seismic loading.

The research team included Professor Hoe Ling of Columbia University, Dr. Mohri of the National Research Institute of Rural Engineering in Tsukuba City, Japan, and the author. Detailed results were reported by Leshchinsky, et al. (2009) and Ling, et al. (2009).

Ideally, the design of any structure subjected to earthquakes should be based on tolerable recoverable and/or permanent displacements. This approach is difficult to implement for reasons such as a lack of acceptable criteria for tolerable displacements, highly random future seismic record, inaccurate identification of in situ soil constitutive behavior, and numerical difficulties in predicting displacements within the matrix soil-geosynthetic. The state-of-the-art in seismic slope stability analysis is not yet sufficiently developed to entirely replace the current design practice.

Design of slopes is typically based on limit equilibrium (LE) stability analysis. Pseudostatic slope stability analysis assumes an equivalent seismic coefficient, typically in the horizontal direction, which results in additional force components in the limit equilibrium equations, all proportional to gravity. Specifying the seismic coefficient as peak ground acceleration (PGA) is likely overly conservative as it considers the maximum seismic forces permanent rather than momentary.

The objective of this study was to quantify a reasonable reduction factor (RF) on the PGA for geocell retention structures. Reduced factors can then be integrated with well-established LE analysis to conduct seismic and static design.