INTRODUCTION

       Although EPS-block geofoam for road construction is an established technology and despite the extensive and continuing worldwide use of EPS-block geofoam, it has been underutilized in U.S. practice because a comprehensive design guideline and a material and construction standard for its use as lightweight fill in roadway embankments has been unavailable. Therefore, there was a need in the U.S. to develop formal and detailed design documents as well as an appropriate material and construction standard for use of EPS-block geofoam in roadway applications.

      To meet this need, the American Association of State Highway and Transportation Officials (AASHTO), in cooperation with the Federal Highway Administration (FHWA), funded National Cooperative Highway Research Program (NCHRP) Project 24-11 titled “Guidelines for Geofoam Applications in Embankment Projects.”  The NCHRP research was conducted from July 6, 1999 to August 31, 2002 by the research team of Timothy D. Stark, David Arellano, John S. Horvath, and Dov Leshchinsky.

      The results of this NCHRP project are presented in two reports. One report includes only the design guideline and the material and construction standard for use of geofoam in stand-alone roadway embankments (Available at http://trb.org/publications/nchrp/nchrp_rpt_529.pdf). The second report includes the background and analyses used to develop the design guideline and material and construction standard as well as a summary of the engineering properties of EPS-block geofoam and an economic analysis of geofoam versus other lightweight fill materials (Available at http://trb.org/publications/nchrp/nchrp_w65.pdf).

      An example of the extensive use of the NCHRP Project 24-11 deliverables is the use of EPS-block geofoam on the Central Artery/Tunnel (CA/T) project. This project is the first major project to use the NCHRP Project 24-11 research results into practice. The CA/T project experience produced both improvements in existing knowledge and new knowledge that will be formally documented and incorporated into the proposed new work.

      The same research team has been assembled to extend this geofoam research to the use of geofoam in slope stabilization as part of NCHRP Project 24-11(02) titled “Guidelines for Geofoam Applications in Slope Stability Projects.”

 PROJECT OBJECTIVE

       The objective of this research is to develop a comprehensive document that provides both state-of-the-art knowledge and state-of-practice design guidance to engineers for the use of EPS-block geofoam for the function of lightweight fill in slope stability applications. This document will include a design guideline as well as an appropriate material and construction standard.         

      The document will facilitate the use of geofoam in highway projects by providing engineers with the five primary research products required to ensure successful technology transfer, i.e., summary of relevant engineering properties, a comprehensive design guideline, a material and construction standard, economic data, and a detailed numerical example.

OVERVIEW OF RESEARCH APPROACH

             To accomplish the research objective and to facilitate implementation of the research results into practice, the research will consist of two phases and ten tasks.

The objective of Phase I is to review, document, and synthesize the worldwide experience of using EPS-block geofoam as lightweight fill in slope stability applications and develop an interim design guideline and material and construction standard. Phase I will consist of the following six tasks: (1) perform literature search, (2) summarize design methods, (3) summarize geofoam construction practices, (4) review and modify the NCHRP Project 24-11 recommended EPS-block geofoam material and construction standard, (5) perform an economic analysis of geofoam versus other light-weight fill material for slope stabilization purposes, and (6) prepare an interim report that summarizes the results of Phase I. The first phase is to consist primarily of a literature review and a geofoam usage survey which is to be conducted via a questionnaire to obtain case history information, cost data, design details, and other geofoam related information. The Phase I report will serve as an interim design document pending completion of the final report.

            The objective of Phase II is to develop a comprehensive design methodology to optimize both the technical performance and cost of geofoam for slope stabilization through the development of a comprehensive design guideline including design and analysis procedures for the use of EPS-block geofoam as lightweight fill in slope stability applications. Phase II will consist of the following four tasks: (7) perform applicable geofoam analysis, (8) develop a design algorithm, (9) develop routine geofoam design aids, such as slope stability design charts, and (10) prepare a final report that summarizes the results of Phases I and II that can be published and distributed by the NCHRP. The results of Phase II will be integrated with the Phase I results to modify the interim design guideline and standard developed in Phase I.