Geofoam Applications in the Design and Construction of Highway Embankments (2004)

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ix GUIDELINES FOR GEOFOAM APPLICATIONS IN EMBANKMENT PROECTS SUMMARY Construction of roadway embankments on soft foundation soils, such as peats or soft clays, has long been problematic. The two main approaches for coping with the problem is to improve the engineering properties, e.g., shear strength and compressibility, of the foundation soils or reduce the weight of the embankment and thus the load applied to the problematic foundation soils. Because of the uncertainty involved in using ground improvement techniques, DOTs and other owners have been increasingly using lightweight fills to reduce the weight of the embankment. The level of uncertainty involved in ground improvement techniques, e.g., quantifying the increase in foundation shear resistance, is high relative to the use of lightweight fill because strengthening of the foundation can be difficult to control and the soil strata may not be known accurately. In addition, the improvement in the engineering properties of the foundation soils must be verified prior to embankment construction to ensure satisfactory performance. Conversely, the properties and geometry of man-made lightweight fills, e.g., geofoam, are well defined which provides more confidence and less uncertainty in its use than foundation improvement techniques. The reduced uncertainty is mainly caused by the fill being so light that it does not stress the foundation and thus the need to accurately know the soil strata and engineering properties is significantly reduced or eliminated. There are a large number of potential lightweight fill materials available. However, EPS- block geofoam usage has been increasing for a number of reasons including it exhibits the lowest density/unit weight and thus the smallest impact on the soft foundation soils, exhibits consistent material properties because it is manufactured, is easy and fast to construct even in adverse weather conditions, results in decreased maintenance costs as a result of less settlement from the

x low density of EPS-block geofoam, alleviates the need to acquire additional right-of-way to construct flatter slopes because of the low density of EPS-block and/or the use of a vertical embankment, applies less lateral stress to bridge approach abutments, can be used over existing utilities which reduces or eliminates utility relocation, and exhibits excellent durability. EPS- block geofoam has been used as lightweight fill worldwide since at least 1972, which corresponds to a road project in Norway. The use of EPS-block geofoam in the U.S.A. for the lightweight fill application dates back to at least the 1980s although at least two conceptual U.S. patents for the use of plastic foams as lightweight fill were issued in the U.S.A. in the early 1970s. Since the Norwegian roadway project in 1972, the Japanese constructed their first lightweight fill project in 1985. Approximately ten years later, geofoam usage in Japan comprises approximately 50 percent of the worldwide usage. In the U.S. approximately 10 percent of annual sales of block molded EPS is now used in the geofoam market versus none approximately ten years ago. Objectives of the Report Despite the continuing worldwide use of EPS-block geofoam, a specific design guideline or design procedure for its use as lightweight fill in roadway embankments was unavailable. Therefore, there was a need in the U.S.A. since the mid 1990s to develop a formal and detailed design document for use of EPS-block geofoam in routine practice. The purpose of this report is to fill this void with a comprehensive document that provides both state-of-the-art knowledge and state-of-practice design guidance for engineers. This document presents a design guideline as well as an appropriate material and construction standard, both in AASHTO format. It is anticipated that this document will encourage greater and more consistent use of EPS-block geofoam in roadway embankments. The ultimate benefit of this is an optimization of both the technical performance as well as cost of EPS-block geofoam embankments. It is anticipated that designers will be more willing to consider EPS-block geofoam as an alternative for construction of embankments over soft ground using the design methodology and material and construction standard presented herein.

xi Organization of Report The report is divided into two parts. The first part of the report, which consists of thirteen chapters, is concerned with the design of EPS-block geofoam roadway embankments. Chapter 1 provides an overview and history of the use of EPS-block geofoam for roadway embankments and discusses appropriate terminology. Chapter 2 presents a summary of the engineering properties that are necessary to implement the proposed design methodology, such as, modulus, elastic limit stress, Poisson’s ratio, and interface shear resistance. Chapter 3 provides an overview of the design methodology developed herein for embankments on soft soil incorporating EPS-block geofoam. The design methodology consists of the following three main parts: pavement system design (Chapter 4), external stability evaluation (Chapter 5), and internal stability evaluation (Chapter 6). All three of these considerations are interconnected and must be considered for each geofoam embankment. Chapter 3 also includes the background for the “Provisional Design Guideline” that is included in Appendix B. Chapter 4 presents the pavement system design module that utilizes both flexible or rigid pavement systems. Chapter 5 presents the external stability considerations, e.g., bearing capacity, settlement, static and seismic slope stability, hydrostatic uplift, translation due to water and wind, that should be evaluated when utilizing an EPS-block geofoam embankment. Finally, Chapter 6 presents the internal stability issues, e.g., static and seismic sliding between the EPS blocks, load bearing capacity of the blocks, sliding due to water and wind, and EPS durability that should be considered. Chapter 7 presents design examples that demonstrate the design methodology outlined in Chapter 3 and detailed in Chapters 4, 5, and 6 for a traditional trapezoidal embankment that can be used by design engineers to facilitate design of their projects. The key feature in Chapters 4, 5, and 6 is the inclusion of design charts that can be used to obtain an optimal design for a geofoam embankment on soft soil. Chapters 8, 9, and 10 discuss geofoam construction practices, MQC/MQA testing, and design details, respectively. These chapters provide the background for understanding the “Provisional Standard” included in Appendix C. Chapter 11 provides a

xii summary of several case histories that have successfully incorporated EPS-block geofoam into roadway embankments and slope stabilization applications. Chapter 12 provides cost information to allow a cost estimate for the geofoam embankment to be prepared during the design phase so that an optimal geofoam design can be selected. The designer can then use this optimal geofoam design to perform a cost comparison with other soft ground construction techniques. Finally, Chapter 13 presents areas of future research for EPS-block geofoam for roadway embankments. The second part of the report is composed of six appendices. Appendix A describes a geofoam usage survey that was developed and distributed during this study and also presents the responses to the survey. Appendix B presents the provisional design guideline for EPS-block geofoam embankments that is outlined in Chapter 3. Appendix C presents the provisional standard for the use of EPS-block geofoam, which should facilitate DOTs in specifying, and thus contracting for the use of geofoam in roadway embankments. Appendix D presents an extensive bibliography of all references encountered during this study that relate to EPS-block geofoam. Finally, Appendix E presents a glossary of the terms used in the report and Appendix F provides conversion factors that can be used to convert between Système International d’Unités (SI) and inch-pound (I-P) units. The key products of the research are the provisional design guideline in Appendix B and the provisional material and construction standard in Appendix C. Designers that desire a quick overview of the design process and/or a recommended material and construction standard can utilize Appendix B and C. Both the Système International d’Unités (SI) and inch-pound (I-P) units have been used in this report. SI units are shown first and I-P units are shown in parentheses within text. Numerous figures are included for use in design. Therefore, only SI units are provided in some of the figures to avoid duplication of figures. Additionally, in some cases figures have been reproduced that use either all SI or all I-P units. These figures have not been revised to show both sets of units. However, Appendix F presents factors that can be used to convert between SI and I-

xiii P units. The one exception to the dual SI and I-P unit usage involves the quantities of density and unit weight. Density is the mass per unit volume and has units of kg/m3 (slugs/ft3) and unit weight is the weight per unit volume and has units of kN/m3 (lbf/ft3). Although density is the preferred quantity in SI, unit weight is still the common quantity in geotechnical engineering practice. Therefore, the quantity of unit weight will be used herein except when referring to EPS-block geofoam. The geofoam manufacturing industry typically uses the quantity of density with the SI units of kg/m3 but with the I-P quantity of unit weight with units of lbf/ft3. Therefore, the same dual unit system of density in SI and unit weight in I-P units will be used when referring to EPS- block geofoam. Concluding Comments The research has amply confirmed that EPS-block geofoam can provide a safe and economical solution to problems with construction of roadway embankments on soft soils. This report is designed to produce a single source of information on the present state-of-the-art knowledge of geofoam usage in roadway embankments. It is important to recognize, that although much progress has been made in the use of geofoam in roadway embankments since the early 1970s, our understanding of all aspects of the behavior and cost/benefits, especially the intangible benefits, of EPS-block geofoam for embankment construction is not complete. For example, there are unanswered questions about the creep characteristics of EPS-block geofoam, seasoning times required prior to shipment, and appropriate testing to determine the small-strain stiffness of EPS blocks for use in the design methodology presented herein. It is anticipated that the information documented herein will serve as a guide to initiate technical advances that will lead to even more efficient designs and increased usage of geofoam in roadway embankments.