John S. Horvath

THE COMPRESSIBLE INCLUSION FUNCTION OF EPS GEOFOAM

Abstract This paper summarizes the state of knowledge for using expanded polystyrene (EPS) geofoam where the primary geosynthetic function provided by the geofoam is compressible inclusion. In general, a compressible inclusion is any material that compresses readily under an applied stress or displacement compared to other materials in contact with, or in the vicinity of, the compressible inclusion. Geotechnical applications for a compressible inclusion include behind earth-retaining structures; around formation elements;; and above pipes, culverts, and tunnels. Using a compressible inclusion can result in significant reduction of earth pressures under static and dynamic loading. A compressible inclusion can also be used to accommodate ground or structure movement. Using a compressible inclusion can be cost-effective for both new construction as well as rehabilitating or upgrading existing structures. Numerous examples are used to illustrate these applications. Because of the inherent multi-functional nature of EPS, there can be additional benefits such as thermal insulation and concomitant cost-savings when EPS geofoam is used as a compressible inclusion.

Expanded Polystyrene (EPS) geofoam: An introduction to material behavior

Abstract The new geosynthetic product category of ‘geofoam’ was proposed in 1992. It encompasses polymeric and non-polymeric foams that are used in geotechnical applications. Geofoams perform functions that traditional geosynthetic products cannot. In addition, geofoams can be used to complement or enhance the function of other geosynthetics. Thus, geofoams used either alone or with other geosynthetics offer new, cost-effective soltions to a wide variety of geotechnical problems. This paper provides an overview of the geotechnically relevant engineering properties of a specific geoform material called expanded polystyrene (EPS), which is a type of ‘rigid’ plastic foam. EPS is the most widely used geofoam material. There is approximately 30 years experience of using it in geotechnical applications, primarily as thermal insulation and ultra-lightweight fill (its density is only about 1% of the density of soil).

Extended Veletsos-Younan Model for Geofoam Compressible Inclusions behind Rigid, Non-Yielding Earth-Retaining Structures

Geofoam is a type of cellular geosynthetic that can be used to reduce lateral earth pressures acting on rigid earth-retaining structures (RERSs) under a variety of soil and load conditions. One of the geosynthetically-functional ways in which geofoams do this is as a compressible inclusion to allow shear-strength mobilization of retained soil through controlled yielding which involves the wellknown soil mechanics mechanism of arching. This paper describes how a mathematical model developed by Veletsos and Younan for a seismic-load application not involving geofoam was modified and extended to create a novel solution involving the use of geofoam as a compressible inclusion. An illustration of how this Extended Veletsos-Younan model can be applied in practice is also included using a case-history and full-scale, 1-g physical tests.

CELLULAR GEOSYNTHETICS IN TRANSPORTATION APPLICATIONS

Cellular geosynthetics is the generic term for geosynthetic materials and products with either a closed- or open-cell texture. This includes the product categories of geofoams and geocombs that are the focus of this paper. Cellular geosynthetics have begun to have a noticeable impact in engineered construction, especially transportation applications. This is because they offer a wide range if geosynthetic functions that, with few exceptions, are unavailable from traditional planar geosynthetics such as geogrids, geomembranes and geotextiles. This paper summarizes the geofoam and geocomb materials and products that are available currently, and highlights their functions and typical applications on transportation related projects with an emphasis on new trends and developments.

GEOFOAM COMPRESSIBLE INCLUSIONS: THE NEW FRONTIER IN EARTH RETAINING STRUCTURES

A compressible inclusion in the broadest sense of the term is any relatively compressible material that is intentionally placed between a rigid and/or non-yielding structure and the ground that would otherwise be in direct contact with it. This allows the ground to yield or displace. The primary benefit is reduced earth pressures acting on the structure which can either reduce the cost of a new structure or enhance the performance of an existing one. This paper outlines the basic ways in which modern, engineered compressible inclusions are used with earth-retaining structures to produce controlled yielding and predictable results. Typical materials used, which nowadays are usually some type of geofoam geosynthetic, and specific transportation-related applications are also described. Because of the diversity of applications and the fact that there are usually multiple benefits to using them, the use of geofoam compressible inclusions has the potential to significantly and permanently impact they way in which earth-retaining structures are designed, constructed, maintained, rehabilitated, and upgraded.

Seismic Lateral Earth Pressure Reduction on Earth-Retaining Structures Using Geofoams

Geofoam is a type of cellular geosynthetic that can be used to reduce lateral earth pressures acting on a wide range of earth-retaining structures (ERSs). There are two distinct geosynthetic-functional ways in which geofoams can provide this benefit: as lightweight fill and as a compressible inclusion. These functions can be implemented either in new construction or retroactively with existing ERSs. Depending on the specific design details chosen, it is possible to reduce lateral earth pressures acting on an ERS to almost zero under both gravity and seismic loading. Unfortunately, the existence and capabilities of this geotechnology, which has the potential to revolutionize the way ERSs are designed, are still not widely known and thus have been significantly underutilized to date. This paper summarizes the state of knowledge concerning the use of geofoams to reduce lateral earth pressures on ERSs and addresses both analytical methods (with an emphasis on seismic loading) as well as geofoam materials and products. It is hoped that this will encourage both usage and research of this intriguing geotechnology.

Framework for Design Guideline for Expanded Polystyrene Block Geofoam in Slope Stabilization and Repair

This paper presents the framework for the interim design guideline for the use of expanded polystyrene (EPS) block geofoam for slope stabilization and repair, based on the findings of the NCHRP Project 24-11(02) Phase I study. The overall objective of this research is to develop a design guideline as well as an appropriate material and construction standard for the use of EPS block geofoam for the function of lightweight fill in slope stability applications. The recommended design methodology included in the framework is based on an assessment of the existing technology and literature. The Phase II work will refine the interim design guideline framework and address some uncertainties in the current state of the practice of analyzing various failure mechanisms included in the design procedure. The completed research will consist of the following five primary research products: (a) a summary of the relevant engineering properties, (b) a comprehensive design guideline, (c) a material and construction standard, (d) economic data, and (e) a detailed numerical example. No formal design guidelines on the use of any type of lightweight fill for slope stabilization by reducing the driving forces are available. Therefore, the proposed interim design guideline for EPS block geofoam can serve as a blueprint for the use of other types of lightweight fills in slope stability applications. The NCHRP Project 24-11(01) and the Project 24-11(02) Phase I research confirmed that EPS block geofoam is a unique lightweight fill material and can provide a safe and economical solution for slope stabilization and repair.

Computer software for load-deformation and geothermal analyses in problems involving geosynthetics

Abstract Software for analyzing two classes of problems, with each incorporating one or more types of geosynthetic products, is discussed. The classes of problems are the load-deformation behavior of earthworks and retaining structures and thermal analysis of soil masses. Comments on actual use of the software as well as sources for purchase are included.